Article

Novel CoS2 Embedded Carbon Nanocages by Direct Sulfurizing Metal-organic Framework for Dye-sensitized Solar Cells

Article

Novel CoS2 Embedded Carbon Nanocages by Direct Sulfurizing Metal-organic Framework for Dye-sensitized Solar Cells

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Abstract

Owing to its excellent electrocatalytic properties, cobalt disulfide (CoS2) is regarded as a promising counter electrode (CE) material for dye-sensitized solar cells (DSSCs). However, hindered by its relatively poor electrical conductivity and chemical instability, it remains a challenge to apply it into high-performance DSSCs. In this work, we have developed novel CoS2 embedded carbon nanocages as a CE in DSSCs, using ZIF-67 (zeolitic imidazolate framework 67, Co(mim)2, mim = 2-methylimidolate) as a template. The CoS2 samples sulfurized for different time lengths are prepared through a facile solution process. It is found that the sulfurization time can be optimized to maximize the DSSC efficiency and the DSSC based on the CoS2 embedded carbon nanocages sulfurized for 4 hours exhibits the highest photovoltaic conversion efficiency (PCE) of 8.20%, higher than those of DSSCs consisting of other CoS2 CEs and Pt-based DSSC (7.88%). The significantly improved DSSC PCE is contributed by the synergic effect of inner CoS2 nanoparticles and an amorphous carbon matrix, leading to a CE with high catalytic activity, good electrical conductivity and excellent durability. This study demonstrates that the CE based on inexpensive CoS2 embedded carbon nanocages is a prospective substitute to expensive platinum and provides a new approach for commercializing high-efficiency DSSCs.

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... The other way is to design the nanostructure of the electrocatalyst for I 3 − reduction regarding with the charge transfer route and the surface area. Transition metal compounds (TMCs) possess d-electron filling in e g orbitals, which promote excellent electrocatalytic performance in partially filled condition [4,19,[21][22][23][24]. So, they are interested to replace Pt. ...
... But most of TMCs still show poorer electrocatalytic ability than Pt. To overcome the challenge, TMCs are synthesized with various nanostructure, which is an important factor for increasing electrocatalytic ability [20][21][22]25]. A nanostructure is defined if any dimension of the structure is lower than 100 nm, the structure is the nanostructure. ...
Chapter
Full-text available
Nowadays, the requirement of energy increases every year, however, the major energy resource is fossil fuel, a limiting source. Dye-sensitized solar cells (DSSCs) are a promising renewable energy source, which could be the major power supply for the future. Recently, the transition metal component has been demonstrated as potential material for counter electrode of platinum (Pt)-free DSSCs owing to their excellent electrocatalytic ability and their abundance on earth. Furthermore, the transition metal components exist different special nanostructures, which provide high surface area and various electron transport routs during electrocatalytic reaction. In this chapter, transition metal components with different nanostructures used for the application of electrocatalyst in DSSCs will be introduced; the performance of electrocatalyst between intrinsic heterogeneous rate constant and effective electrocatalytic surface area are also be clarified. Final, the advantages of the electrocatalyst with different dimensions (i.e., one to three dimension structures) used in DSSCs are also summarized in the conclusion.
... Fig. 5(b) exhibit the high-resolution spectrum of Co2p. The peaks at around 794.2 and 779.1 eV (x = 0.04) as well as 793.7 and 778.9 eV (x = 0.06) are consigned to the Co2p 1/2 and Co 2p 3/2 of Co 3+ species [35]. While the peaks at 795.6 and 780.7eV (x = 0.04) and 795.1 and 780.0 eV (x = 0.06) are corresponds to the Co 2p 1/2 and Co 2p 3/2 of the oxidized cobalt species i.e Co 2+ [35]. ...
... The peaks at around 794.2 and 779.1 eV (x = 0.04) as well as 793.7 and 778.9 eV (x = 0.06) are consigned to the Co2p 1/2 and Co 2p 3/2 of Co 3+ species [35]. While the peaks at 795.6 and 780.7eV (x = 0.04) and 795.1 and 780.0 eV (x = 0.06) are corresponds to the Co 2p 1/2 and Co 2p 3/2 of the oxidized cobalt species i.e Co 2+ [35]. Besides, two satellite peaks were also detected close to Co 2p peaks that are in agreement with literature [36]. ...
Article
In this work the nanocrystalline particles of BiFO3 co-doped with ytterbium and cobalt Bi1-xYbxFe1-xCoxO3 (x=0.0, 0.02, 0.04, 0.06, 0.08) were synthesized via sol-gel method. The phase purity and crystallinity of the synthesized particles were examined by X-ray diffraction (XRD) technique. The values of the diffraction peaks match precisely with the standard data (JCPDS card no.-71-2494). XRD data also ensures the formation of rhombohedral symmetry of R3C space group. Raman spectra over the frequency range of 800-1600 cm⁻¹ have been systematically investigated with different excitation wavelengths. For determining vibrational modes of the doped nanoparticles, Raman scattering spectra at excitation wavelengths λ= 532nm was recorded. FESEM images reveal the fact that, x=0.02 doping significantly reduces the grain size resulting high surface area for active sites.X-ray photoelectron spectroscopy (XPS) was also carried out to estimate the compositions and the valence states of elements in Bi1-xYbxCoxFe1-xO3 (x=0.04, and 0.06) nanoparticles. The substitution of Yb³⁺ and Co²⁺ ions in BFO nanocrystalline samples, improves the magnetic and photocatalytic properties. The entire range of visible light wavelength absorption is observed in all the synthesised nanoparticles and were analysed by UV-Visible absorption spectroscopy. The energy band gap was found to be ∼2.30 eV for pure BFO, which get altered by Yb³⁺ and Co²⁺ substitution and found to be ∼1.88 eV in case of Bi0.94Yb0.06Fe0.94Co0.06O3 nanoparticle. The photocatalytic properties get enhanced with the substitution of Yb³⁺and Co²⁺ in BFO, that may be due to change in energy band gap and formation of trapping sight, which results into increase in the number of electron hole pair and hence improve the photocatalytic properties.
... Extending to the utilization of carbon nanotubes as done in previous work made byLee et al[23], Cui et al[25] utilized cobalt disulfide (CoS 2 ) embedded carbon nanotubes sulfurized with ZIF-67 MOF (Zeoliticimidazolate framework 67, Co(min) 2 , min=2-methylimidolate) as counter electrode (CE) in a DSSC thatachieved significantly better efficiency. Here, the sulfurization time of CoS 2 was optimized to maximize the efficiency of DSSC and it was found that the DSSC based on CoS 2 embedded carbon nanotubes which was sulfurized for 4 hrs exhibited the highest PCE of 8.2 per cent compared to other CoS 2 CEs and Pt-based DSSC, where it was 7.88 per cent.This significant improvement was because of the synergic effect of inner CoS 2 nano particles and an amorphous carbon matrix which resulted in high catalytic activity, good electrical conductivity with excellent durability. ...
Article
The introgression of metal–organic frameworks (MOFs) in dye-sensitized solar cells has received greater attention over the past decade. Many efforts have been made to improve the performance of these cells by optimizing its different components viz. photosensitizer, photoanode, and counter electrode. This article provides the recent advances in each of these major directions achieved through MOF and its hybrid components in dye-sensetized solar cells.
... Obviously, it was evidenced that the distinctive CAN network remained in gC 3 N 4 nanosheets even after the doping of sulfur [50]. The S-gC 3 N 4 / CoS 2 -II nanocomposite material exhibits all characteristics due to S-gC 3 N 4 and an additional peak at 1097 cm À1 corresponds to Co@S stretching vibration; which indicates the formation of CoS 2 over S-gC 3 N 4 framework [51]. ...
Article
This work demonstrates a high-performance hybrid asymmetric supercapacitor (HASC) workable in very high current density of 30 A g−1 with in-situ pyrolytic processed sulfur-doped graphitic carbon nitride/cobalt disulfide (S-gC3N4/CoS2) materials and bio-derived carbon configuration and achievement of high electrochemical stability of 89% over 100,000 cycles with the coulombic efficiency of 99.6%. In the electrochemical studies, the S-gC3N4/CoS2-II electrode showed a high specific capacity of 180 C g−1 at 1 A g−1 current density in the half-cell configuration. The HASC cell was fabricated using S-gC3N4/CoS2-II material and orange peel derived activated carbon as a positive and negative electrode with a maximum operating cell potential of 1.6 V, respectively. The fabricated HASC delivered a high energy density of 26.7 Wh kg−1 and power density of 19.8 kW kg−1 in aqueous electrolyte. The prominent properties in specific capacity and cycling stability could be attributed to the CoS2 nanoparticles engulfed into the S-gC3N4 framework which provides short transport distance of the ions, strong interfacial interaction, and improving structural stability of the S-gC3N4/CoS2-II materials.
... [63] [191] For one electrode, the faradaic efficiency of the HER was also evaluated. It was achieved by measuring at fixed time intervals, the volume of gas that evolved at the cathode during potentiostatic electrolysis. ...
Thesis
The advancement of renewable energy sources run by solar or wind energy, unevenly accessible throughout the day or year, should go in hand with the development of new energy storage systems. Moreover, various modern electronic devices, which are gradually becoming elements of everyday life, must nowadays meet the high requirements of multifunctionality, portability and flexibility. Their rapid development, combined with the increased energy consumption, entails the need to develop new energy storage methods that largely affect the functionality of these devices.[4][5] The operation of many new energy conversion and storage technologies is based on the same, fundamental electrochemical reactions, such as the hydrogen evolution reaction (HER), oxygen evolution reaction (OER) or oxygen reduction reaction (ORR). All of the above-mentioned reactions are characterised by their quite complex mechanism and sluggish kinetics, and therefore their practical application depends on the electrocatalytic properties of their constituent electrode materials. Innovations in the field of hydrogen fuel cells, which effectively convert the chemical energy of hydrogen molecules into electric energy, have extended the interest in hydrogen as a fuel. Their biggest advantage in this application is their particularly high (unachievable by batteries or other chemical fuels) energy density per unit weight. Therefore, since 2014, cars powered by hydrogen fuel cells have been mass-produced, and their share in the car market is constantly growing. Apart from innovative applications, hydrogen is also still indispensable in high-volume branches of industry, such as ammonia production, petrochemistry or metallurgy. Despite the trend of the increasing consumption of this chemical, 95% of its production is still generated from the processing of non-renewable resources. Due to their shrinking supplies, there is a demand for the development of an effective method of hydrogen production from renewable resources. The technology of water electrolysis, during which water molecules are split into hydrogen and oxygen, meets this requirement. Nonetheless, its large-scale application is limited by high energy consumption in the process (which to some extent can be reduced with the use of proper electrocatalysts) and the cost of the electrocatalysts themselves. The benchmark electrocatalysts of the HER and OER are the platinum-group metals, which are not only expensive but also scarce in the environment. Therefore, there is an urgent need of developing novel, effective and widely available noble metalfree electrocatalytic materials. Nowadays, promising HER and/or OER electrocatalytic materials are non-noble metal compounds, modified carbon materials, and their composites. Current research on electrocatalysts is usually focused on powder materials. However, in order to apply them in electrochemical reactions, the powders require attachment to the electrode surface in order to assure the electron flow. The attachment is usually performed using polymer binders, which can increase the charge transfer resistance and hinder the diffusion of reagents to the electrode surface at which the electrocatalytic reaction occurs. Therefore, this thesis focuses on the synthesis and investigation of electrocatalytic materials in the alternative form of free-standing electrodes. The electrodes are prepared by (1) the direct modification of carbon fibre cloth, aimed at formation of fully metal-free electrodes, and (2) the formation of composite electrodes by directly depositing electrocatalytically active non-noble metal-based films on a modified carbon cloth surface. Different electrode preparation procedures are optimised in order to obtain high-performance electrodes and, based on a physicochemical and electrochemical characterisation of the electrode series, to draw the conclusions on the material properties determining the electrocatalytic activity.
... They can be ascribed to the coexistence of Co 3+ (779.1 and 794.2 eV) and Co 2+ (780.9 and 797.1 eV) [33]. Moreover, the peaks located at binding energy of 784.8 and 803.0 eV can be ascribed to satellite peaks of Co 2p 3/2 and Co 2p 1/2 , respectively [34,35]. As the orange dotted line illustrated in Figure 2b, it is visible that the Co 2p 1/2 peak of Se-CoS 2 NW/CF shifts slightly to the higher binding energy region compared to that of CoS 2 NW/CF. ...
Article
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The pursuit of low-cost and high-efficiency catalyst is imperative for the development and utilization of hydrogen energy. Heteroatomic doping which is conducive to the redistribution of electric density is one of the promising strategies to improve catalytic activity. Herein, the Se-doped CoS2 porous nanowires array with a superaerophobic surface was constructed on carbon fiber. Due to the electronic modulation and the unique superaerophobic structure, it showed improved hydrogen evolution activity and stability in urea-containing electrolyte. At a current density of 10 mA cm−2, the overpotentials are 188 mV for hydrogen evolution reaction (HER) and 1.46 V for urea oxidation reaction (UOR). When it was set as a cell, the voltage is low as 1.44 V. Meanwhile, the current densities of HER and UOR, as well as of cell remained basically unchanged after a continuous operation for 48 h. This work opens up a new idea for designing of cost-saving hydrogen evolution electrocatalysts.
... This value of R u is the result of the combining effect of contact resistance between the catalyst and electrode substrate, the resistance of the electrode substrate, and the resistance offered by the bulk catalyst. Given that all other factors are constant value of R u can be used as an indicator of electrical conductivity of catalyst film [56]. Charge transfer resistance on the other hand is the resistance associated with electron transfer from the electrode to the electrolyte. ...
Article
An efficient, cost-effective, and more readily available electrocatalysts that can lower the overpotential associated with oxygen evolution reaction (OER) is a prerequisite for the application of water splitting for hydrogen production at a larger scale. Herein, we demonstrate a composite electrode obtained by anchoring polyhedral Fe3O4 particles on nickel foam (NF) is a highly active catalyst for OER. Notably, this catalyst was able to achieve a current density of 10 mA cm⁻² and 100 mA cm⁻² at a low overpotential of 251 and 310 mV. Also, Fe3O4-NF displayed a low Tafel slope of 45 mV dec⁻¹. Moreover, at an overpotential of 300 mV Fe3O4-NF showed a turnover frequency (TOF) of 3.12 ×10⁻³ s⁻¹ suggesting that Fe3O4-NF has a high intrinsic catalytic activity which is on par with commercial RuO2 catalyst. Furthermore, due to the close contact and strong adhesion between Fe3O4 and NF, the Fe3O4-NF displayed good stability during OER. The post-activity characterizations indicate that iron oxyhydroxide (Fe(O)OH) formed due to in-situ oxidation of Fe3O4 surface functions as the active catalytic phase whereas, bulk of the catalyst acts as a conducting scaffold.
... The multichannel structure can notably improve the accessibility to electrolyte of active materials and provide shortened ion diffusion paths. Meanwhile, the dodecahedron structure of ZIF-67 embedded on the nanofibers loses some edges and corners, then appears to become a hollow polyhedron (Fig. 1d) [39]. The Co 1− x S HPs are anchored on nanofibers tightly with homogeneous intervals to each other. ...
Article
The exploration of prospective electrode materials represents great challenges for remarkable lithium-ion batteries (LIBs) and sodium-ion batteries (SIBs). Herein, we report a reliable synthetic approach for the in-situ growth of the Co-based zeolitic imidazolate framework (ZIF-67) on electrospun nanofibers, followed by carbonization and sulfurization with the formation of free-standing Co1−xS hollow polyhedrons anchored on multichannel carbon nanofibers (Co1−xS/MCF) for LIBs and SIBs. The Co1−xS/MCF electrode displays a high reversible capacity (813 mAh g⁻¹ over 180 cycles at 0.1 A g⁻¹), and stable cycle performance (559 mAh g⁻¹ for 300 cycles at 1 A g⁻¹) in LIBs. For SIBs, Co1−xS/MCF electrode exhibits a favorable Na-storage capacity (433 mAh g⁻¹ over 120 cycles at 0.1 A g⁻¹). The as-prepared binder-free Co1−xS/MCF anode demonstrates the advanced electrochemical properties for LIBs and SIBs. It is attributed to the particular multichannel nanostructure and the Co1−xS hollow polyhedrons (Co1−xS HPs), which provide enough active sites, and the internal void space effectively reduces the structural strain and eases the volume expansion to maintain structural integrity. This work gives insights to design a unique structure for promising LIBs and SIBs.
... To fulfill these functions, the CE should possess some basic requirements: high catalytic activity, high conductivity, high reflectivity, low-cost, high surface area, porous nature, optimum thickness, chemical, electrochemical and mechanical stability, chemical corrosion resistance, energy level that matches the potential of the redox couple electrolyte, and good adhesivity with TCO. 113 Carbon materials (i.e., grapheme, carbon nanotubes, carbon black), 114 metals and alloys, 115 metal oxides, sulfides and selenides, 116,117 transition metal compounds, 118 conductive polymers (such as polyaniline, 119 polypyrrole, 120 poly(3,4ethylenedioxythiophene) 121 ), and composite materials are the most studied materials as counter electrodes. 112 2.2. ...
Article
Continual escalation of our world population demands a vast and safe energy supply, the majority of which has been produced by fossil fuel sources. However, because of the huge energy demand, exponential depletion of these nonrenewable energy sources is inescapable and forthcoming in the coming century. Hence, utilization of renewable energy such as solar energy has gained attention because of its direct conversion of light energy into electrical power without any harmful environmental impacts. Solar energy has been harvested by different types of solar cells varying from inorganic to organic to the combination of both. Among them, the dye-sensitized solar cell (DSSC) with a biopolymer-based electrolyte has gained enormous consideration from researchers because of its sustainability, abundance of available raw material, low production cost, and easy production in addition to the low volatilization of electrolytes compared to liquid state electrolytes. This review aims to give an overview of the recent inputs in the development of biopolymer-based DSSCs. The performance of the biopolymers as electrolytes in DSSCs will be critically reviewed based on the physicochemical properties of the biopolymers. Key technical challenges and future research areas for the advancement of biopolymer-based DSSCs are also discussed.
... In the FTIR spectra ( Fig. 1D), the peaks at 851 and 551 cm À1 are attributed to the bending vibration of CeH and OeH bonds of the remained acetate molecules in the system, respectively [42]. Based on the FTIR spectra, the remained acetate was removed from the system by increasing the annealing temperature up to 240 C. Besides, the peak located at around 1134 cm À1 is assigned to the cobalt-sulfur stretching vibration in the CoS 2 structure [43]. The intensity of the cobalt-sulfur bond in the sample annealed at 200 C for 24 h is more than the samples annealed at 160 C and 240 C, indicating that the optimum temperature of the annealing process is 200 C. ...
Article
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h i g h l i g h t s g r a p h i c a l a b s t r a c t A simple hydrothermal process was used to synthesize CoS 2. Experimental conditions were changed to investigate electro-activity of CoS 2 for HER. The reaction time and temperature somewhat affected the elec-trocatalytic activity. Co(Ac) 2 improved efficiency by 34 and 72% over Co(Cl) 2 and Co(NO 3) 2 , respectively. Crystal size and active sites are key reasons for changes in electroactivity. Available online xxx a b s t r a c t In this study, cobalt disulfide (CoS 2) nanostructures are synthesized using a simple hy-drothermal method. The effects of experimental parameters including cobalt precursor, reaction times, and reaction temperatures are investigated on the structure, morphology and electrocatalytic properties of CoS 2 for hydrogen evolution reaction (HER). The characterization of as-prepared catalysts is performed using X-ray diffraction (XRD), energy dispersive X-ray spectroscopy (EDS), scanning electron microscopy (SEM), Fourier transform infrared (FT-IR), and X-ray photoelectron spectroscopy (XPS). The HER efficiency of the catalysts is examined using linear sweep voltammetry (LSV) and electrochemical impedance spectroscopy (EIS) methods in 0.5 M H 2 SO 4 solution. Furthermore, Cobalt disulfide (CoS 2) Hydrothermal Synthesis condition Efficient electrocatalyst chronoamperometry (CA) is used for stability evaluation. The catalyst obtained from cobalt acetate precursor, within 24 h at 200 C exhibits superior electrocatalytic activity with a low onset potential (139.3 mV), low overpotential (197.3 mV) at 10 mA. cm À2 and a small Tafel slope of 29.9 mV dec À1. This study is a step toward understanding the effect of experimental parameters of the hydrothermal method on HER performance and developing optimal design approaches for the synthesis of CoS 2 as a common electrocatalyst.
... More specifically, the first peak at 781.3 eV (2p 3/2 ) was J Mater Sci: Mater Electron fitted into two peaks at 779.0 and 782.3 eV with a satellite (Sat) peak at 786.6 eV. Similarly, the second peak at 796.9 eV (2p 1/2 ) was deconvoluted into two peaks at 795.2 and 797.4 eV with a Sat peak at 803.0 eV [34,35]. These Sat peaks (786.6 and 803 eV) of Co 2p 3/2 and Co 2p 1/2 corresponded to the diffraction peaks at 6.6 and 6.1 eV, respectively, indicating the presence of Co 2? in mp-Co 3 S 4 [36]. ...
Article
Full-text available
A high-capacity and mesopore-rich electrode material is crucial for constructing hybrid supercapacitors (HSCs) with high energy densities. Developing mesopore-rich cobalt sulfides can increase the effective contact area for surface redox reactions. However, incorporating mesopores in metal sulfides is challenging owing to the low affinity between metals and sulfur. Herein, a simple strategy to fabricate mesoporous cobalt sulfide (mp-Co3S4) was proposed. The mp-Co3S4 exhibited the specific capacities of 246.2 mAh g−1 (at a current density of 1 A g−1) and delivered remarkable energy and power densities (32.5 Wh kg−1 and 596.94 W kg−1, respectively) when used as an electrode for an HSCs device, showing an excellent cycle life and capacity retention of 84% after 3000 cycles. In addition, unique structure of the fabricated mp-Co3S4 provided sufficient electrochemically active sites and enhanced the cycle stability of the constructed HSC device. This template-free synthesis of mp-Co3S4 can be used to fabricate other transition metal sulfides.
... 39,44 The synchrotron-based quasi-in situ Fourier transform-infrared (FT-IR) spectrum also revealed that Co-O bonds appeared after OER while Co-S bonds remained (Fig. S22, ESI †). 45,46 Additionally, XPS data were further collected to explore the composition and reveal the chemical state of CSST-14. In the high-resolution Co 2p XPS spectra (Fig. S23, ESI †), a pair of peaks located at 780.5 and 795.6 eV could be assigned to b-CoOOH. ...
Article
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The ambiguous mechanism of electrocatalysts for the oxygen evolution reaction (OER) greatly hinders their industrial applications toward renewable and clean energy conversion. Here, we elaborately prepared a cobalt sulfide catalyst to perform a comprehensive study of the OER performance under neutral/alkaline conditions. The combination of synchrotron-based operando X-ray spectroscopic investigations and electron microscopy observations captured a chameleon-like structural self-optimization on the cobalt sulfide oxygen evolution electrocatalyst in both neutral and alkaline electrolytes. Driven by the actual working conditions (pH gradient, electrical potential, etc.), distinct catalytic sites could be activated dramatically. In particular, the CoOOH supported on a single-walled carbon nanotube (CoOOH-SWCNT) with residual S species was identified as the true catalyst under alkaline conditions rather than the entirely transformed CoOOH-SWCNT, while the oxygenated CoS-SWCNT (O-CoS-SWCNT) was formed as the true catalyst under neutral conditions. Undoubtedly, such a mechanism of opening different locks with different keys and its microstructural advantages together guarantee the high catalytic activity in different electrolytes. This work provides a promising catalyst as well as sheds light on the very essence of the structural self-optimization process of catalysts. It makes a significant contribution to the advancement of OER relevant studies in the future while providing new ideas for the fields of chemistry and catalysis.
... Power conversion efficiencies of the Zn-TCPP-Pt thin film CE was measured 5.48 and 4.88% under front-side and rear-side irradiation, respectively. To overcome the poor conductivity and short chemical stability of CoS2, Cui et al. [169] exploited a groundbreaking approach: they loaded CoS2 into carbon nanocages using ZIF-67 as surfactant. They tested different treatment times and after 4 h they obtained the highest photovoltaic conversion efficiency (PCE) of 8.20%, higher than those of DSSCs made up of other CoS2 CEs and Pt-based DSSC (7.88%). ...
Article
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Metal-organic frameworks (MOFs) and covalent organic frameworks (COFs) are two innovative classes of porous coordination polymers. MOFs are three-dimensional materials made up of secondary building blocks comprised of metal ions/clusters and organic ligands whereas COFs are 2D or 3D highly porous organic solids made up by light elements (i.e., H, B, C, N, O). Both MOFs and COFs, being highly conjugated scaffolds, are very promising as photoactive materials for applications in photocatalysis and artificial photosynthesis because of their tunable electronic properties, high surface area, remarkable light and thermal stability, easy and relative low-cost synthesis, and structural versatility. These properties make them perfectly suitable for photovoltaic application: throughout this review, we summarize recent advances in the employment of both MOFs and COFs in emerging photovoltaics, namely dye-sensitized solar cells (DSSCs) organic photovoltaic (OPV) and perovskite solar cells (PSCs). MOFs are successfully implemented in DSSCs as photoanodic material or solid-state sensitizers and in PSCs mainly as hole or electron transporting materials. An innovative paradigm, in which the porous conductive polymer acts as standing-alone sensitized photoanode, is exploited too. Conversely, COFs are mostly implemented as photoactive material or as hole transporting material in PSCs.
... The first one of these categories includes 2 constant phase elements Q1 and Q2. Whilst the second group includes 3 resistances namely R s which is the uncompensated solution resistance whose value is marked by a point in the high-frequency region of the Nyquist plot with zero impedance [70]. The other two resistances R 1 and R 2 reflect the resistance to the charge transfer and mass transfer respectively [7,71]. ...
Article
Herein, we provide a facile pathway to transform waste onion skins into a competent and stable electrocatalyst for the OER. The obtained catalyst had a core-shell structure wherein, Fe-Fe3C particles were encased within shells of N-doped carbon (FO800). Due to the synergetic interplay among its components, FO800 displayed excellent OER activity. Notably, FO800 delivered the current density of 10 mA cm⁻², and 50 mA cm⁻² at a low overpotential of 330 mV, and 380 mV with a Tafel slope of 52 mV dec⁻¹. Moreover, at an overpotential of 350 mV FO800 displayed a turnover frequency of 0.02 s⁻¹ indicating that FO800 possesses high intrinsic activity which is comparable to that of RuO2. Owing to the presence of a protective carbon shell FO800 displayed excellent stability for 24 h. The role of Fe3C, N doping, and C shell, in determining the overall OER activity was also examined. Our experimental observations suggest that the incorporation of Fe3C in the N-doped carbon improves the charge transfer efficiencies at the electrode-electrolyte interface by increasing the Donor density.
... As shown in Supplementary Figure 8, the deconvolution plot of the C 1s XPS spectra for S@SG-CNT shows four peaks at 289.0, 286.7, 285.6, and 284.7 eV, which correspond to O-C=O, C=O, C-O/C-S, and C=C/C-C bonds, respectively. The occurrence of C-S bonds suggests that S atoms were doped in SG-CNT and formed a robust bond during the high-temperature treatment [35] . The O 1s XPS spectrum for the S@SG-CNT [Supplementary Figure 9] is deconvoluted into three peaks at 531.2, 533.2, and 534.3 eV, which are assigned to C=O, C-O-C (epoxide), and HO-C=O groups (carboxyl), respectively [26] . ...
Article
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The lithium-sulfur battery is currently considered to be a promising candidate for next-generation energy storage devices. However, its commercial application is severely restricted by rapid capacity decay mainly arising from unavoidable dissolution of intermediate lithium polysulfide of the S-based cathodes. Herein, multifunctional stripped grapheme-carbon nanotubes (SG-CNT) with 1D/2D interwoven and hierarchical pore structure as a promising host to stabilize S was constructed by cheaper raw materials and a facile strategy. Based on comprehensive analysis, the interwoven network and hierarchical pores along with abundant oxidative functional groups in matrix provided large contact area with S, short transport pathway for electrons/Li-ions, sufficient space to accommodate volumetric change, and superior confinement ability for S/polysulfides, thus resulting in effectively stabilizing the S cathode with high S loading and increasing its utilization. Therefore, the S@SG-CNT cathodes exhibited a high reversible capacity of 1227 mAh g-1 at 0.1 A g-1 , excellent cyclability with a capacity of 773 mAh g-1 after 500 cycles at 0.2 A g-1 , and ultra-long cycling performance with capacity decay less than 0.01% per cycle at 2 A g-1. This facile strategy and unique construction of superior performance cathode provide a new avenue for next commercial application.
... The satellite peaks at around 785.6 and 803.9 eV are related to the oxidation state of Co, which may be caused by oxidation caused by air contact [38]. The appearance of S2p peaks at 163.2 eV and 162.0 eV indicates the formation of S 2 2-, while the peak values at 169.4 eV and 168.2 eV are S-O generated by surface air exposure (Fig. 3b) [39]. Furthermore, It can be observed from the XPS spectra (Fig. 3c) of CoS 2 after adsorption that Co2p, Co2p 3/2 , and Co2p 1/2 spectra all show the characteristic peak moving up to higher binding energy. ...
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High-efficiency electrocatalysts for Li–S batteries have great significance for improving their electrochemical performance and cycle stability. Here, a hollow CoS2 nanosphere as a novel electrocatalyst for the cathode host material of high-performance Li–S batteries was obtained by a two-step strategy of solvothermal and sulfuration. Different from the traditional light carbon materials, the tap density of CoS2@S composite material has reached 1.17 g cm⁻³. The high tap density of CoS2@S nanospheres composite guarantees the high volume energy density. Specifically, a hollow nanosphere has a large internal space which provides the possibility for a large load of the active material (80.66 wt%). Besides, electrochemical kinetics evaluation indicated CoS2 nanospheres are beneficial for promoting Li–S electrochemical heterogeneous conversion and accelerating the diffusion of lithium ions in the cathode, both of which can help to keep the battery cycle stable and long life. Moreover, the chemical interaction between Co ions and polysulfides can effectively anchor the adsorbed polysulfides, which can help immobilize sulfur species and restrain the shuttle effect. Such a rationally prepared CoS2 nanosphere is significant for promoting the electrochemical performance of the sulfur cathode due to high-volume energy density and rapid kinetic transformation promoting action. As a result, the CoS2@S composite exhibits high volume energy density and excellent performance under high sulfur load (4.8 mg cm⁻²) and low E/S ratio (electrolyte/sulfur = 10 μL mg⁻¹) based on of the composite as cathode host materials. This work provides a new idea for the exploration of cathode host materials with high volume energy density and high electrochemical performance for lithium–sulfur batteries.
... eV and 163.4/164.6 eV (Fig. 6g), belonging to2p 3/2 and 2p 1/2 from CoS 2 and NiS 2 , respectively [40,41]. We assigned peaks at 169.9 and 168.7 eV to S-O generated by the contact of sulfide with air [42]. As shown in Fig. 6h, four fitted peaks (288.6 eV, 286.6, 285.8, and 284.7) in the C 1s spectra were assigned to O = C -O, C = O, C -N/C-S, and C -C, respectively [43,44]. ...
Article
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Featuring high electrical conductivity and electrochemical activity, transition metal sulfides are promising materials for the positive electrode of hybrid supercapacitors. However, considering their poor cycling life and rate performance, critical challenges remain. In this contribution, we describe hollow NiS2/CoS2@C composites obtained by stepwise etching, annealing, and sulfuration of ZIF-67. Specifically, NiS2/CoS2 particles were dispersed on N/S co-doped carbon nanocages and found to exhibit outstanding stability and rate performance. The unique nanocage structure of N/S co-doped carbon and heterogeneous interfaces of NiS2 and CoS2 can promote both ion transport and electron transfer, enriching the active site to enhanced reactivity. The resulting NiS2/CoS2@C nanocage composites in fact showed excellent electrochemical performance. The specific capacity of NiS2/CoS2@C was achieved 1373 C g⁻¹ at 1 A g⁻¹. When combined with reduced graphene oxide (RGO)-based negative electrode, the assembled hybrid supercapacitor expressed an energy density of 63.3 Wh kg⁻¹ at a power density of 800 W kg⁻¹, with a high residual capacity exceeding 98% of the initial capacity even after 13,000 cycles.
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Exploration of counter electrode (CE) catalysts with excellent reduction activity to S n ²⁻ and low charge transfer resistance ( R ct ) is always a major challenge for the development of quantum dot sensitized solar cells. In this work, coral-like CoSe 2 - nitrogen-doped porous carbon hydrides (CoSe 2 -NC) were successfully prepared by two-step calcination of zeolitic imidazolate framework (ZIF), including carbonization and selenization process. Scanning electron microscopy shows that the CoSe 2 -NC catalyst presents a coral-like microscopic morphology composed of nanospheres. Electrochemical impedance spectroscopy displays that the CoSe 2 -NC CE presents a low R ct of 1.04 Ω. The PCE of the QDSSC based CoSe 2 -NC CE is up to 5.06%,which is 26%, 87% higher than those of CoSe 2 and NC CEs. The enhanced photovoltaic performance is attributed to the unique coral-like structure and the synergistic catalytic effect of CoSe 2 and NC.
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Hollow functional materials with adjustable morphologies based on transition metal sulfides have been considered as a class of attractive and promising electrocatalysts for multifarious energy conversion devices. Herein, we adopt a facile template-engaged method to synthesize morphology-tunable Ni–Fe–WSx hollow nanoboxes by changing the mass ratios (1/1, 1/2 and 1/3) of nickel iron Prussian-blue analog precursors and (NH4)2WS4. During the above processes, (NH4)2WS4 acted as a multifunctional vulcanizator to supply elements of S and W simultaneously and the surface of Ni–Fe–WSx nanoboxes became rougher with the increment of WS4²⁻. Noteworthy, profiting to the moderated surface morphology, appropriate doped ratio and the synergistic effect of multiple elements, Ni–Fe–WSx-2 hollow nanoboxes not only possessed higher specific surface and well-defined interior voids but also performed excellent catalytic properties on promoting the reduction of I3⁻ comparing to Ni–Fe–WSx-1, Ni–Fe–WSx-3 and Ni–Fe–S in dye-sensitized solar cells (DSSCs). As expected, the DSSC prepared with a Ni–Fe–WSx-2 counter electrode (CE) possessed a higher value of power conversion efficiency (PCE) about 9.86% which was more remarkable than that of Pt (8.20%).
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Dye-sensitized solar cells (DSSCs) and perovskite solar cells (PSCs) favor minimal environ-mental impact and low processing costs, factors that have prompted intensive research and development. In both cases, rare, expensive, and less stable metals (Pt and Au) are used as counter/back electrodes; this design increases the overall fabrication cost of commercial DSSC and PSC devices. Therefore, significant attempts have been made to identify possible substitutes. Carbon-based materials seem to be a favorable candidate for DSSCs and PSCs due to their excellent catalytic ability, easy scalability, low cost, and long-term stability. However, different carbon materials, including carbon black, graphene, and carbon nanotubes, among others, have distinct properties, which have a significant role in device efficiency. Herein, we summarize the recent advancement of carbon-based materials and review their synthetic approaches, structure-function relationship, surface modification, heteroa-toms/metal/metal oxide incorporation, fabrication approaches, and effects on photovoltaic ef-ficiency, based on previous studies. Finally, we highlight the advantages, disadvantages, and design criteria of carbon materials and fabrication challenges that inspire researchers to find low cost, efficient and stable counter/back electrodes for DSSCs and PSCs.
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Due to the low material cost, simple preparation process and no pollution to the environment, dye-sensitized solar cells (DSSCs) have become one of the important power conversion devices. The counter electrode (CE, also called cathode), an important part of DSSCs, plays a critical role in the photovoltaic performance of DSSCs. Platinum (Pt) with high electrocatalytic activity is the most commonly used CE material in DSSCs, which suffers from the problems of high price and poor stability, highlighting the importance of developing novel low-cost, active and stable Pt-free CEs. In this work, a series of A-site deficient (La0.8Sr0.2)1-xFeO3-δ (x = 0, 0.02, 0.05, 0.1) perovskite oxides are designed to serve as CEs in DSSCs. Through investigating the influence of the A-site deficiency on the power conversion efficiency (PCE), it is found that the introduction of an appropriate deficiency in perovskite oxides is beneficial for catalytic activity of triiodide (I3−) reduction reaction (IRR) of the CE, thus improving the photovoltaic performance of DSSCs. Consequently, the (La0.8Sr0.2)0.98FeO3-δ/multiwalled carbon nanotubes (MWCNTs) CE-based device exhibits the highest PCE of 8.22% while the Pt-based device which only yields a PCE of 7.21%. The significantly enhanced efficiency of DSSCs is mainly attributed to the synergistic effect between the high oxygen vacancy concentration and the appropriate amount of Fe4+ as well as reduced particle size, which enhances the charge transfer capability and the I3− diffusion capability simultaneously. Furthermore, the decent IRR durability of (La0.8Sr0.2)0.98FeO3-δ/MWCNTs composites confers the corresponding DSSCs an excellent long-term stability. This work provides a facile way to design active and durable Pt-free perovskite oxide-based CEs in DSSCs, which may lay the foundation for the commercialization of DSSC technology.
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The transition metal selenides have aroused wide concern due to their potential characteristics in the energy storage and conversion. The formation of multivariate MOFs attracts much research attention and provides the essential guarantee for multivariate mixed-metal selenides. Herein, a series of isostructural MOF-74 materials with different divalent metals were prepared by changing the molar ratios of nickel to cobalt. After selenizing, CoSe2, NiSe2 and three kinds of mixed-metal selenides were easily obtained, prompting us to systematically research the effect of different metal species and molar ratios on the electrochemical performance of the mixed-metal selenides. It is found that mixed-metal selenides derived from MOF-74 display much better performance than single metal selenides, and NiCoSe-4 with a Ni/Co molar ratio of 4:1 demonstrates a high specific capacity of 211 mAh g⁻¹ at a current density of 1 A g⁻¹. What's more, the assembled asymmetric supercapacitor NiCoSe-4//AC shows a high energy density of 61.24 Wh kg⁻¹ at power density of 800 W kg⁻¹, which suggests that NiCoSe-4 as a promising electrode material possesses further research value and potential for practical applications in energy storage fields.
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Exploring high efficient transition-metal dichalcogenides catalysts for hydrogen evolution reaction (HER) is important for water-derived hydrogen fuel. Pyrite cobalt disulfide (CoS2) is one of the potential HER catalysts due to its low price and inherent metallicity, but its catalytic activity is still unsatisfactory possibly attributed to the S sites with catalytic inert; hydrogen adsorption on S sites is weak extremely. Metal cation doping has been considered as one of the most available methods to modulate the electronic structure of electrocatalysts. Here, we report non-transition metal tin (Sn) doped CoS2 nanowire arrays grown on carbon cloth (Sn-CoS2/CC) as available catalysts for HER. The Sn-CoS2/CC catalyst with optimal doping concentration not only has an enhanced over potential of 161 mV at 10 mA cm⁻², and the Tafel slope is 94 mV dec⁻¹, but also shows good long-term durability in 32 hours of testing. Experimental results and further density functional theory (DFT) calculations show that Sn doping can improve the charge transfer ability, enhance electronic conductivity, and arouse the catalytic insert S sites with optimal hydrogen adsorption free energy (ΔGH*). This work investigates a new method to activate the inert sites in metal-compound catalysts for water splitting and beyond through non-transition metal doping.
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Lithium sulfur battery provides one of the most attractive opportunities for next generation energy storage devices benefiting from its particularly high energy density. However, the obstacle mainly originating from the sluggish conversion kinetics between soluble lithium polysulfides immediate and S/Li2S/Li2S2, results in a lithium sulfur battery with low sulfur usage and coulombic efficiency, poor cycling and rate performance. In this work, a new cathode host material with cobalt disulfide nanoparticles supported on reduced graphene oxides is designed to enhance the interactive affinity to lithium polysulfide and accelerate polysulfide conversion more effectively. With the implementation of this metal chalcogenides, a sulfur cathode with low polarization, stable cycling performance and high rate capability is obtained. Moreover, this work offers solid evidence from the post mortem analysis of symmetric cells such as SEM, XPS to confirm the origin of the catalytic effects in a sulfur battery.
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The rational design of hybrid structures which consist of multiple components with distinctive characteristics is an effective strategy for developing materials when energy storage applications. In this paper, a novel hierarchical CoS2@Ni(OH)2 core-shell nanotube array covered carbon cloth is successfully designed and synthesized for use in supercapacitors (SCs). The CoS2 nanotube (NT) arrays are synthesized using the metal organic framework template method, and serve as the scaffold for the growth of ultrathin Ni(OH)2 nanosheets via the electrodeposition process. The optimized CoS2@Ni(OH)2 hybrid electrode exhibits high specific capacity of 743 C g⁻¹ at current density of 1 A g⁻¹, which is nearly 5.9 times higher than that of a single CoS2 electrode. In addition, a solid state hybrid supercapacitor device is fabricated with CoS2@Ni(OH)2 hybrid electrode as positive and activated carbon as negative. The as-prepared devices deliver high energy density (29.22 W h kg⁻¹ at 899.2 W kg⁻¹) and high power density (8.99 kW kg⁻¹ at 11.74 W h kg⁻¹), as well as good cycling stability (85.5% retention of specific capacitance after 3000 cycles). The devices also display excellent flexible properties under different bending conditions. The present work shows that electrode materials with hybrid structure have considerable application prospect for flexible energy storage and conversion.
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Developing multifunctional, efficient, inexpensive, and eco-friendly electrocatalyst has become a challenging and crucial task for researchers. Herein, we have designed and developed a NiCo-based NiCo-MOF-Phosphide (NiCo-MOF-P) as a multifunctional electrocatalyst via electrodeposition and phosphorization approach. The structurally and electronically modified NiCo-MOF-P can significantly boost the electrocatalytic activity towards urea-assisted water splitting. The optimized electrocatalyst exhibits a lower overpotential of 230 mV for OER and delivered a current density 10 mA cm⁻² at applied potential of 1.32 V for UOR. When, catalyst was used as cathode and anode, it requires a cell voltage of 1.45 V to reach the current density of 10 mA cm⁻² for urea-assisted full water splitting (230 mV less than that of urea free counterpart) with remarkable long time stability. The NiCo-MOF-P also exhibits an overpotential 191 mV to achieve a current density of 10 mA cm⁻² for HER in an alkaline medium.
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The low conductivity and catalytic activity of counter electrode (CE) materials in the electrolyte of dye-sensitized solar cells (DSSCs) has resulted in unprecedented challenges, limiting their development. Herein, a highly efficient CE material was synthesized by uniformly distributing transition metal selenides in a metal-organic framework (MOF, denoted as [email protected]), and then integrating carbon nanotubes, which were finally designed as integrated interconnected nanoreactors ([email protected]). Consequently, DSSC with three-dimensional (3D) reticular [email protected] CE displayed a superior power conversion efficiency (PCE) of 9.25%, exceeding that of Pt CE (7.81%). This outstanding performance is attributed to: (1) the increased specific surface area, which promotes the absorption of the dye and electrolyte, (2) the metal-on-MOF hierarchical structure as a unique crystalline porous material, which optimizes the efficiency of the metal nanoparticles, (3) the doping of heteroatom (N), which provides more defect sites and enhances the catalytic activity, and (4) the porous walls of MOF and internal connected CNTs, which provide sufficient pathways for the fast diffusion of electrons and iodine ions. The present work not only strengthens the understanding of the coupling interaction between porous [email protected] and CNTs, but also offers an extended strategy of structuring further well-defined metal-on-MOF hybrids.
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Bio-Dye is a dye derived from natural ingredients that have an important role in DSSC performance. This Bio-Dye is later in charge of absorbing sunlight entering the DSSC cells. Bio-Dye is a dye derived from natural ingredients that have an important role in the performance of the DSSC. This Bio-Dye is the one that will be in charge of absorbing sunlight entering the DSSC cells). One important key to know DSSC performance is to pay attention to the quality of the BIO-Dye. A good BIO-Dye can be seen by knowing the absorbance pattern and the function group of the dye its self. This research was conducted to determine absorbance patterns and functional groups based on pH variations in the wet and dry extraction methods contained in the Ocimum sanctum . The absorbance pattern was seen using a UV-Vis spectrophotometer and a functional group using FTIR. The chlorophyll pigment contained in the BIO-Dye ( Ocimum sanctum leaf) was extracted using an ethanol solvent and added acetic acid to produce variations in pH values. The UV-Vis spectrometer measurement results showed the highest absorbance pattern was possessed by Ocimum sanctum dye in the dry extraction method and at natural pH (pH = 6.5). The peak absorbance they have is 648 nm, 614 nm, and 537 nm. The FTIR spectrum was obtained from Ocimum sanctum information containing the same functional groups when variations in pH values were carried out in the wet and dry extraction methods. The functional groups are OH groups at wave number 3356.57 cm ⁻¹ , CH at 2975.37 cm ⁻¹ , C = O at 1652.50 cm ⁻¹ , CN at 1383.81 cm ⁻¹ , C = C at 880.25 cm ⁻¹ , and CH absorbed at wave number 1087.78 cm ⁻¹ . In general, it can be concluded that natural dye from Ocimum sanctum has a high absorbance in the visible light region and contains COOH compounds that can strengthen the bond of dye with TiO 2 semiconductors so that Ocimum sanctum can be used as a dye in Dye-Sensitized Solar Cells (DSSC).
Chapter
Hydrogen production through water splitting using renewable energy sources is the cleanest and the most efficient way to store energy. However, slow kinetics of the hydrogen and oxygen evolution reaction (HER and OER, respectively) require the use of a catalyst, and the most efficient are Pt-based materials (HER) and Ru/Ir oxides (OER). The high cost and scarcity of these noble metals hinder the application of water splitting devices and make the development of new competitive, active, and stable catalysts essential. Therefore, a great focus has been given to the production of nonoxide electrocatalysts with high HER and OER activity and, in this chapter, we expected to provide a wide description of the existing technology, the advantages, and limitations of each group of materials, and the perspectives and future applications of these oxides free materials in electrochemical water splitting devices. This chapter will concentrate on the fundamental electrochemical water splitting process, with an overview of the hydrogen and oxygen evolution reactions, the state-of-the-art catalysts, and present the recent advances in nanostructured nonoxide materials based on borides, borates, chalcogenides (sulfides and selenides), phosphides, phosphates, nitrides, carbides, alloys, and MOF-structured nanoparticles produced and highly employed as catalysts for the electrochemical water splitting.
Article
The luxury price, shortage, and instability of platinum (Pt) markedly hamper its commercialization in dye-sensitized solar cells (DSSCs). Consequently, developing an efficient alternative catalyst in lieu of noble Pt is imperative issue for the promotion of DSSCs. In this paper, a robust and electrochemically stable 3D nanocomposite comprised of amorphous ruthenium sulfide nanoparticles (RuS2 NPs), reduced graphene oxide (RGO), and functionalized multi-walled carbon nanotubes (MWCNTs) was prepared by the facile hydrothermal method and explored as a counter electrode (CE) in DSSCs. The RuS2 NPs uniformly decorated on the surfaces of the RGO/MWCNTs to form the RuS2/RGO/MWCNTs composite, which adequately inhibited aggregation of the RuS2 NPs to fully exploit its impressive electrochemical activity. Benefiting from the unexceptionable catalytic activity of RuS2 NPs in the RuS2/RGO/MWCNTs as well as superior electronic transmission channels provided by the conductive RGO/MWCNTs network, the designed DSSC with RuS2/RGO/MWCNTs exhibited a remarkable power conversion efficiency (PCE) of 13.24 % exceeding that of Pt CE (PCE: 9.53 %). Consequently, this research opens a new avenue to fabricate advanced cathode catalysts based on metallic sulfides and carbon-based materials with excellent performance for their potential application in next-generation energy storage and conversion devices such as DSSCs, water splitting, and other electrochemical applications.
Article
Covalent organic frameworks (COFs) are of great interest in the energy and optoelectronic fields due to their high porosity, superior thermal stability, and highly ordered conjugated architecture, which are beneficial for charge migration, charge separation, and light harvesting. In this study, polyimide COFs (PI-COFs) are synthesized through the condensation reaction of pyromellitic dianhydride (PMDA) with tris(4-aminophenyl) amine (TAPA) and then doped in the TiO2 photoelectrode of a dye-sensitized solar cell (DSSC) to co-work with N719 dye to explore their functionality. As a benchmark, the pristine DSSC without the doping of PI-COFs exhibits a power conversion efficiency of 9.05% under simulated one sun illumination. The doping of 0.04 wt % PI-COFs contributes an enhanced short-circuit current density (JSC) from 17.43 to 19.03 mA/cm2, and therefore, the cell efficiency is enhanced to 9.93%. The enhancement of JSC is attributed to the bifunctionality of PI-COFs, which enhances the charge transfer/injection and suppresses the charge recombination through the host (PI-COF)-guest (N719 dye) interaction. In addition, the PI-COFs also function as a cosensitizer and contribute a small quantity of photoinduced electrons upon sunlight illumination. Surface modification of oxygen plasma improves the hydrophilicity of PI-COF particles and reinforces the heterogeneous linkage between PI-COF and TiO2 nanoparticles, giving rise to more efficient charge injection. As a result, the champion cell exhibits a high power conversion efficiency of 10.46% with an enhanced JSC of 19.43 mA/cm2. This methodology of increasing solar efficiency by modification of the photoelectrode with the doping of PI-COFs in the TiO2 nanoparticles is promising in the development of DSSCs.
Chapter
Dye-sensitized solar cells (DSSCs) were first invented in 1991 by Gratzel and coworkers. The environmental friendliness, cost-efficient, and easy fabricate properties of these solar cell have attracted by the many researchers. Typically, DSSCs consist of four components: the photoanode consisting of a wide-bandgap semiconductor, the sensitizer acting as a light harvester, the electrolyte containing the redox couple for dye regeneration, and the counterelectrode. Although many materials have been used in DSSCs until today, the most used traditionally components are TiO2 photoanode, N719 ruthenium-based metal complex dye, I3⁻/I⁻ redox mediator, and Pt counterelectrode. Solar cell efficiency of about 14% were obtained with this type of DSSCs. MOF constructs were developed at the same time as DSSCs. MOF structures are used in many fields due to their unique surface, electrochemical, and physicochemical properties. For this purpose, MOF structures are used especially to increase the performance of DSSCs. In this book chapter, the effects of using MOFs in DSSC construction on the working mechanisms of DSSCs as well as their efficiency are examined in detail. A perspective has been drawn for the future use of MOF structures in DSSC manufacturing and the directions in which applications will advance.
Chapter
The metal-organic-frameworks (MOFs) have been investigated as potential material for various types of solar cells, including dye sensitized solar cells (DSSCs). The MOFs are excellent precursors for deriving metal oxides, carbides, sulfides and other composites. The MOFs have been implemented in DSSCs either as the working electrode, counter electrode, sensitizer or the electrolyte. The book chapter gives a brief overview of DSSCs and its working mechanism. It describes the synthesis process and properties of MOFs that make them a suitable choice for DSSCs. The latest development in this field will be presented with focus on the fundamentals of the technology, i.e., the optoelectronic properties of MOFs that are necessary to obtain high performance solar cells. The challenges highlighted in the end of the chapter provides a direction for carrying out future research in this field.
Article
Electrochemical H2 production from water splitting is an environmentally sustainable technique but remains a great challenge due to the sluggish anodic oxygen evolution reaction (OER). Replacing the OER with the thermodynamically more favorable electrocatalytic oxidation process is an effective strategy for highly efficient H2 generation. Herein, Mn-doped CoS2 has predicted an excellent bifunctional electrocatalyst for the hydrogen evolution reaction (HER) and the hydrazine oxidation reaction (HzOR). With the introduction of Mn, the Gibbs free energy of the adsorbed H* and the potential rate-limiting step (the dehydrogenation of *NH2NH2 to *NHNH2) for the HzOR process of the catalyst can be significantly reduced. As expected, the Mn-CoS2 catalyst exhibited excellent catalytic activity and robust long-term stability for the HER and HzOR. In detail, the Mn-CoS2 catalyst only acquired potentials of 46 and 77 mV versus the reversible hydrogen electrode for achieving a current density of 10 mA cm⁻² for the cathodic HER and anodic HzOR, respectively. In addition, the Mn-CoS2 electrode only needs a cell voltage of 447 mV to output 200 mA cm⁻² in the overall hydrazine splitting system as well as exhibits a robust long-term H2 production. This work provides theoretical guidance for the design of advanced bifunctional electrocatalysts and promotes high efficiency and energy-saving H2 production technology.
Article
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For large-scale applications, dye-sensitized solar cells (DSSCs) require the replacement of the scarce platinum (Pt)-based counter electrode (CE) with efficient and cheap alternatives. In this respect, low-cost perovskite oxides (ABO3) have been introduced as promising additives to composite-based CEs in Pt-free DSSCs. Herein, we synthesized composites from La0.9Ce0.1NiO3 (L) perovskite oxide and functionalized-multiwall-carbon-nanotubes wrapped in selenides derived from metal-organic-frameworks (f-MWCNT-ZnSe-CoSe2, “F”). L and F were then mixed with carbon black (CB) in different mass ratios to prepare L@CB, F@CB, and L@F@CB composites. The electrochemical analysis revealed that the L@F@CB composite with a mass ratio of 1.5:3:1.5 exhibits better electrocatalytic activity than Pt. In addition, the related DSSC reached a better PCE of 7.49% compared to its Pt-based counterpart (7.09%). This improved performance is the result of the increase in the oxygen vacancy by L due to the replacement of La with Ce in its structure, leading to more active sites in the L@F@CB composites. Moreover, the F@CB composite favors the contribution to the high electrical conductivity of the hybrid carbon nanotube–carbon black, which also offers good stability to the L@F@CB CE by not showing any obvious change in morphology and peak-to-peak separation even after 100 cyclic voltammetry cycles. Consequently, the corresponding L@F@CB-based device achieved enhanced stability. Our work demonstrates that L@F@CB composites with a low cost are excellent alternatives to Pt CE in DSSCs.
Chapter
Third-generation solar cells have gained promising momentum in recent decades as an inexpensive replacement for conventional silicon wafer-based technology. In particular, dye-sensitized solar cells (DSSCs) have attracted considerable attention owing to their simpler manufacturing procedure, inexpensiveness, and competing power conversion efficiency. The overall device performances of the DSSCs rely on four major components, which are photoanodes, sensitizing dyes, electrolytes, and counter electrodes. The final device completion constituent is the counter electrode – one of the major component, which determines the power conversion efficiency of the device. The final output of DSSCs has been measured through the counter electrode characteristics such as efficient charge transfer and reduction of electrolytes during the energy conversion process. In general, platinum (Pt) is the most commonly used counter electrode in DSSCs due to its superior catalytic property, charge transfer characteristics, and high conductivity. However, for a cost-effective solar cell application, the usage of a noble metal such as Pt is an expensive choice of candidate; and for the reduction of expensiveness, the search for alternative inexpensive material is inevitable. In this review article, we have presented the recent research developments of promising Pt-free metal chalcogenide-based counter electrodes; and the prospects in this emerging field have been discussed. In addition, this review devotes to exploring the novel concepts of various metal chalcogenides; and their composite with other materials such as metal nanoparticles, carbonaceous materials, and doped metal chalcogenide counter electrodes are described.
Chapter
Fossil fuel energy large consumption is one of the major menacing factors for the global warming/energy crisis issues in the recent days that restricts the growth of next-generation storage devices. To meet such energy crises demand, the progress of a new class of electrode materials for renewable energy sources is highly required. This particular chapter enlightens the current progress and recent trends in nanostructured negative electrode materials for lithium-ion battery (LIB) applications. Especially, we deal with metal-free oxides such as transition metal chalcogenides and phosphides which are knowing to be the auspicious anode candidates for rechargeable LIBs owing to their safety features and excellent theoretical capacities. Nevertheless, commercialization of these anode materials-based batteries is hugely limited by their initial capacity fading and poor cycle life. Henceforth, different methodologies to synthesis strategies of materials with various nanostructures, their morphological effect and cycling behaviors for LIBs are necessary to improve the performance of LIBs and explained in detail. The initial capacity fading and retention properties of various metal oxide-free anodes have been reviewed.
Article
The nanoparticles of zeolitic imidazolate framework (ZIF-67) were synthesized and added to ethanolamine/deep eutectic solvent solution to form nanofluid system. The dynamic removal performance of prepared nanofluid system for hydrogen sulfide was investigated. For the system based on choline chloride and urea, the introduction of nanoparticles showed significant enhancement effect on the desulfurization performance. The optimal mass fraction of nanoparticles in nanofluid systems were identified as 0.1%. Besides, the experimental results showed that the prepared nanofluid systems have high regeneration performance, and the presence of moderate moisture is beneficial to the regeneration process. The absorbents and nanoparticles before and after absorption were characterized by Fourier transform infrared spectra, nuclear magnetic resonance, scanning electron microscope, energy dispersive spectrum, X-ray diffraction and X-ray photoelectron spectroscopy. The characterization results showed that the surface of nanoparticle was covered by CoS2 after absorption.
Article
To achieve both high capacity and long cycling stability in sodium-ion batteries (SIBs), the structural optimizations of anode materials should take into considerations of the reaction kinetics, the insertion/extraction processes of Na+, and the structural stability of anodes. In this study, the growth of CoS2 nanoparticles on N-doped graphite carbon three-dimensional nano-skeleton (CoS2/NGC) is designed to increase the active sites for sodium storage, to provide high ionic/electrical conductivity, and to alleviate the volume swelling and reduce Na+ diffusion energy barrier. As employed as anode materials of SIB, CoS2/NGC shows a great rate capability, affording an initial capacity of 660 mAh g⁻¹, and maintaining a coulombic efficiency of 99.7% even after 1000 cycles at 1.0 A g⁻¹. The cyclic voltammetry experiments demonstrate that the main contribution of the capacity is from the capacitive charge-storage. Density functional theory calculations reveal that the advantageous Na⁺ storage kinetics of the CoS2/NGC electrode is attributed to its low Na⁺ adsorption energy of -2.21 eV and low Na⁺ diffusion barrier of 0.113 eV. This systematic study paves a way for the efficient design of metal sulfides anodes for SIB, which is conducive to develop battery systems with remarkable electrochemical performance.
Article
The photoelectric conversion efficiency (PCE) of dye-sensitized solar cells (DSSCs) can be remarkably improved by optimizing the catalytic activity and charge transfer ability of the counter electrode (CE) materials. The attentive hotspots of CE catalysts for DSSCs are to design multifunctional materials that balance the fabrication cost, environmental friendliness, PCE, and electrochemical stability, then to achieve the substitution of the benchmark Pt. In this review, the four effective strategies are highlighted for further improving the photovoltaic performance of the DSSCs based on low-cost CE materials, such as heteroatom-doped materials, development of noble metal-free chalcogenides with well-controlled facets, construction of heterostructure, and synthesis of composites with a synergistic effect. In some typical examples, the influence of these strategies on catalytic activity, charge transfer ability, and reaction mechanism are elucidated by the theoretical calculation. Then the research opportunities and the challenges for the high-efficiency DSSCs based on low-cost CE materials are presented.
Article
Synthesis of non-precious metal materials with cost-effective and excellent electrocatalytic activity as counter electrode (CE) of dye-sensitized solar cells (DSSCs) remains a challenge. Herein, MOF-based self-sustaining template and ion exchange method are developed to fabricate Co9S8 and Ni9S8 loaded on N-doped porous carbon nanocage materials (Co9S8/Ni9S8@C-N) with large specific surface area and remarkable catalytic activities to the reduction of I3⁻ ions. The excellent performance of Co9S8/Ni9S8@C-N is owing to the synergistic effect of Ni9S8 and Co9S8 can further improve the catalytic activity and N-doped porous carbon nanocage as a good conductor provides a suitable place for the redox reaction and guarantees the stability of the material. As a CE catalytic material, Co9S8/Ni9S8@C-N reveals excellent catalytic activity and stability, making the photoelectric conversion efficiency (PCE) 17.54% higher than Pt CE. The Co9S8/Ni9S8@C-N composite material reveals the remarkable potential as a CE in the DSSCs.
Article
The hierarchical polymetallic sulfide electrocatalysts are endowed with high expectations in various energy conversion/storage fields. Herein, a facile two-step solvothermal method was employed to synthesize a series of hierarchical transition metal sulfide nanospheres with defined-well yolk-shelled structures (Co9S8-Ni3S2@WS2, Co9S8@WS2 and Ni3S2@WS2). Noteworthily, the resultant samples as the bifunctional electrocatalysts for the dye-sensitized solar cells possessed prominent electrocatalytic performances. Benefiting from the higher specific surface area, unique morphology, the synergistic effect of multi-elements and more favorable chemical compositions, the quaternary Co9S8-Ni3S2@WS2 nanospheres showed great advantaged features at promoting the reduction of triiodides in comparison with ternary Co9S8@WS2 and Ni3S2@WS2 nanospheres. Among these samples, the counter electrode with Co9S8-Ni3S2@WS2 catalysts exhibited a noteworthy power conversion efficiency of 9.67% for solar cell, which was much superior to that of Pt (8.16%).
Article
The development of bifunctional electrocatalysts with remarkable activity is highly desired for optimal application in overall water splitting, yet challenging. Herein, a unique CoNiP/NF catalyst with advanced feature of hollow well-integration nanostructure on porous Ni foam substrate is reported. Uniform and well-designed 2D cobalt‐based MOF nanosheet are prepared through a simple room temperature static growth, and then the 2D nanosheet arrays are converted into porous 2D nanosheets assembled by 3D microspheres due to ion-exchange and etching process with an additional phosphating. The as-obtained CoNiP/NF nanostructure arrays integrate the advantages of 2D nanosheets and 3D microspheres, modulating the intrinsic electronic structure and further providing rich reaction active sites, which not only promote the permeations of electrolyte, but also promote the evolution/release of gas. When CoNiP/NF as a flexible electrode for electrolysis of water, the nanowall arrays electrode shows remarkable electrochemical performance toward HER and OER with only 147 and 234 mV overpotential at 10 mA cm⁻², respectively, and excellent cycle capability. Moreover, it delivers a much lower cell voltage of 1.62 V to attain 10 mA cm⁻² as superior bifunctional electrocatalyst. Density functional theory (DFT) calculations suggest that the advantages of porous structure can facilitate fast electron transfer and mass transport, further improve electrochemical ability. It can be desired that this work reveals a rational technique to design porous nano-catalysts for hydrogen economy.
Article
A low cost H3PW12O40 (PW12)/CoS2 complex is prepared and used as a counter electrode (CE) to combine with sandwich quantum dot sensitized solar cells (QDSSCs) composed of a TiO2/CdS/CdSe/ZnS photoanode and polysulfide electrolyte to study their photovoltaic properties via a simple hydrothermal method. Under standard simulated sunlight, the photoelectric conversion efficiency (PCE) of 2%PW12 (PW12-2/CoS2) doped CEs was 6.29%, which was significantly 67.7% higher than those of QDSSCs based on undoped CoS2 CEs (3.75%). Due to the introduction of PW12, the nanoparticles forming the hollow structure of CoS2 changed from regular octahedra to rough nanoparticles, which increase the active sites. At the same time, the work function of CoS2 decorated with PW12 is decreased. This study and discovery demonstrate that POMs can be used to optimize CE materials and improve the photoelectric conversion efficiency of QDSSCs, which provide an experimental and theoretical basis for subsequent investigations.
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The cost‐effectiveness and easy availability of MnO2 have attracted researchers′ attention as an anode electrode for LIBs over other transition metal oxides. However, MnO2 usage has been limited to its low reaction reversibility and poor conversion kinetics. Besides, Li‐ion hybrid supercapacitors (LiHSCs) are in urgent demand which offers higher power densities than LIBs without compromising energy density. Among different polymorphs of MnO2, λ‐MnO2, due to its 3D spinel structure, can be applied in many applications. Usually, λ‐MnO2 can be obtained by extracting lithium from LiMn2O4 using complex electrochemical or acid leaching methods. This study presents a modified Li2O2 assisted method to obtain cobalt‐doped 3D architectures of λ‐MnO2 porous hollow nanostructures. The resultant MnxCo1‐xOy hollow structures with 5 % cobalt addition are used as anode for LIBs exhibited excellent charge reversibility and cycle stability over thousands of reaction cycles. This result is known to be one of the finest among MnO2 anodes reported to date. Also, a LiHSC device is fabricated with MnxCo1‐xOy hollow structures as anode and the device exhibits an excellent comprehensive electrochemical performance in terms of high operating voltage (4.2 V), with a specific cell capacity of 33 mAh g−1 at a high current density of 5 A g−1 and achieved the maximum power density of 12261 W kg−1 (with energy density at 81.7 Wh kg−1) with long cycle life. A modified Li2O2‐assisted synthesis method is developed for the preparation of porous hollow cobalt‐doped λ‐MnO2 nanostructures. Co–MnO2 hollow structures offer outstanding performance as anode for the rechargeable lithium‐ion battery by delivering an excellent specific capacity of 1135 mA h g−1 at a high current density 5 A g−1 and achieved an ultra‐high power density of 25.4 kW kg−1 with 60 Wh kg−1 when applied as anode for lithium‐ion hybrid supercapacitor permitting essentially fast recharge with high energy density.
Article
Carbon nanotubes (CNTs) have been far and wide employed as the counter electrodes (CEs) in dye-sensitized solar cells because of their individual physical and chemical properties. However, the techniques available now, such as chemical vapor deposition, arc discharge and laser ablation for synthesizing CNTs, commonly suffer from rigorous operations and complicated steps, which make the process difficult to be controlled. Herein, we present a simple and facile glutamic acid-assisted hydrothermal recrystallization strategy to construct bamboo-like CNTs (GHP-BC-x). Generally, the conventional organic dye 3,4,9,10-perylene tetracarboxylic dianhydride (PTCDA) is used as a precursor and glutamic acid efficiently promotes the recrystallization of the perylene cores’ planar π-conjugated system in PTCDA under hydrothermal conditions and then self-assembles into one-dimensional nanorods with improved crystallization degree, finally resulting in the morphology of bamboo-like CNTs after carbonization. When applied as the counter electrodes, the GHP-BC-3 displays a remarkable power conversion efficiency of 8.25%, benefiting from the superb electrical conductivity and mass transfer dynamics, superior to that of Pt CE (7.62%).
Article
A novel silver fungus-like CoS (SFC) with multiple electrochemically active sites was successfully fabricated by a simple mixed solvent thermal method. Benefiting from the unique porous silver fungus-like microstructure and the good shrinkage characteristics of the fluffy structure, the fabricated SFC electrode demonstrates ideal electrochemical performance for supercapacitors through electrochemical analysis. The material exhibits an outstanding capacitive performance of 350.4 F g⁻¹ at a current density of 1 A g⁻¹ and the assembled asymmetric supercapacitor with SFC and active carbon (AC) as positive and negative electrodes, respectively, achieves a high specific energy of 45.2 Wh kg⁻¹ at a specific power of 1500.0 W kg⁻¹. The study shows that the mixed solvothermal method used to synthesize CoS with a specific porous structure can potentially be extended to other transition metal sulfide-based electrode materials for high-performance supercapacitors.
Article
Seeking inexpensive, cost-effective fabrication, and highly effective Pt-free counter electrode (CE) electrocatalysts to replace the conventional Pt CE for dye-sensitized solar cells (DSSCs) is of great challenge. Here, molybdenum disulfide (MoS2) thin films were directly electrodeposited on F-doped tin oxide (FTO) glass substrates via facile one-step potentiostatic (PS) and potential-reversal (PR) methods, which were exploited as the CE electrocatalysts for DSSC application. According to series of the electrochemical tests, the MoS2 CE electrodeposited by PR mode (PR-MoS2) had a superior electrocatalytic property for I3– reduction in DSSCs to that by PS mode (PS-MoS2). When PR-MoS2 was employed as a CE in a DSSC, the device achieved a satisfactory photoelectric conversion efficiency (PCE) of 8.77%, which is comparable to that based on the conventional Pt CE (9.01%). Meanwhile, the rear side illumination studies showed that the PCE of the DSSC using PR-MoS2 as a CE reached 4.82% and was equivalent to that using the Pt CE (5.67%), which is attributed to their similar transmittance property. This work provides a novel insight into preparing an electrodeposited PR-MoS2-based CE for bifacial DSSCs application.
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Nickel yttria-stabilized zirconia (Ni-YSZ) is used as anode material for solid oxide fuel cells (SOFCs). The electrochemical performance of Ni-YSZ anodes can be improved when the size of constituent particles of nickel is reduced. However, at SOFC high temperature operating environments, nano-sized Ni particles suffer from sintering. Nanoscale Ni-YSZ anodes can undergo severe structure changes. In this work, a unique approach of fabricating a nanostructured Ni-YSZ anode is demonstrated by combining atomic layer deposition (ALD) and glancing angle deposition (GLAD) techniques whereby nickel nanoparticle sintering is prevented at high temperatures with as thin as 1.9 nm YSZ ALD coating on the nickel; the surface area of the resulting Ni-YSZ anode was found to increase more than 3 times that of a planar electrode. In addition, the novel ALD/GLAD coating approach used here provides an ionic conductive YSZ electrolyte phase combined with an electrical conductive Ni phase whereby porosity can be controlled through deposition and post-deposition annealing. In addition, the surface roughness of Ni-YSZ anode decreases with increasing YSZ coating layer thickness and it is unaffected by the post-deposition annealing process. Conductivity measurements of the Ni-YSZ anodes at room temperature show a resistivity in the order of 10-4 cm .S-1.
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The cobalt sulfide nanoflake arrays prepared by the transformation of Co(OH)2 nanoflake arrays using the ion exchange reaction method were incorporated into Pt-free dye-sensitized solar cells (DSSCs). Morphologies and crystal structures of the cobalt sulfide and cobalt hydroxide nanoflakes arrays were characterized by SEM, TEM and XRD analyses, respectively. The electrochemical properties were determined by cyclic voltammetry (CV) measurement. The cobalt sulfide nanoflakes which composed of CoS2 single crystals and their aggregates dispersing in the amorphous cobalt sulfide matrix were completely transferred by substitution of S2- for O2- in the ion exchange reaction. The DSSC assembled with cobalt sulfide nanoflake arrays as the counter electrode showed a photovoltaic conversion efficiency of 5.20%, which was close to that of DSSC with sputtered Pt as the counter electrode (5.34%). Therefore, the cobalt sulfide nanoflake array film can be considered as a promising alternative counter electrode for use in DSSCs due to its large surface area and high electrocatalytic performance.
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We fabricated a highly efficient (with a solar-to-electricity conversion efficiency (η) of 8.1%) Pt-free dye-sensitized solar cell (DSSC). The counter electrode was made of cobalt sulfide (CoS) nanoparticles synthesized via surfactant-assisted preparation of a metal organic framework, ZIF-67, with controllable particle sizes (50 to 320 nm) and subsequent oxidation and sulfide conversion. In contrast to conventional Pt counter electrodes, the synthesized CoS nanoparticles exhibited higher external surface areas and roughness factors, as evidenced by X-ray diffraction (XRD), scanning electron microscopy (SEM) element mapping, and electrochemical analysis. Incident photon-to-current conversion efficiency (IPCE) results showed an increase in the open circuit voltage (VOC) and a decrease in the short-circuit photocurrent density (Jsc) for CoS-based DSSCs compared to Pt-based DSSCs, resulting in a similar power conversion efficiency. The CoS-based DSSC fabricated in the study show great potential for economically friendly production of Pt-free DSSCs.
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Nanoporous carbons (NPCs) have large specific surface areas, good electrical and thermal conductivity, and both chemical and mechanical stability, which facilitate their use in energy storage device applications. In the present study, highly graphitized NPCs are synthesized by one‐step direct carbonization of cobalt‐containing zeolitic imidazolate framework‐67 (ZIF‐67). After chemical etching, the deposited Co content can be completely removed to prepare pure NPCs with high specific surface area, large pore volume, and intrinsic electrical conductivity (high content of sp 2‐bonded carbons). A detailed electrochemical study is performed using cyclic voltammetry and galvanostatic charge–discharge measurements. Our NPC is very promising for efficient electrodes for high‐performance supercapacitor applications. A maximum specific capacitance of 238 F g−1 is observed at a scan rate of 20 mV s−1. This value is very high compared to previous works on carbon‐based electric double layer capacitors. Highly graphitized nanoporous carbons (NPCs) are synthesized by one‐step direct carbonization of cobalt‐containing zeolitic imidazolate framework‐67 (ZIF‐67). After chemical etching, the deposited Co nanoparticles are completely removed to prepare pure NPCs with high specific surface area, large pore volume, and intrinsic electrical conductivity. The specific energy of the NPC‐based supercapacitor reached 19.6 W h kg−1 at a specific power of 700 W kg−1 (see figure).
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Layered double hydroxides (LDHs) are currently attracting intense research interest for their various applications. Three LDH hollow nano-polyhedra are synthesized with zeolitic imidazolate framework-67 (ZIF-67) nanocrystals as the templates. The nanocages well inherit the rhombic dodecahedral shape of the ZIF-67 templates, and the shell is composed of nanosheets assembled with an edge-to-face stacking. This is the first synthesis of the LDH non-spherical structures. And the mechanism of utilizing metal-organic framework (MOF) nanocrystals as templates is explored. Control of the simultaneous reactions, the precipitation of the shells and the template etching, is extremely crucial to the preparation of the perfect nanocages. And the Ni-Co LDH nanocages exhibit superior pseudocapacitance property due to their novel hierarchical and submicroscopic structures.
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Wurtzite CuInS2–ZnS heterostructured nanorods are synthesized via a seed-assisted synthetic route. Cu1.94S–ZnS heterostructured nanorods are transformed into CuInS2–ZnS by reacting with indium ions to convert copper sulfide to wurtzite CuInS2. The shapes of the CuInS2–ZnS heterostructured nanorods can be tuned from burning torch-like to longer rod-like by varying the concentration of added indium. Dye-sensitized solar cells (DSSCs) using these heterostructured nanocrystals as counter electrodes had a power conversion efficiency (7.5%) superior to DSSCs made with conventional platinum electrode (7.1%) under the same device configuration.
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Cobalt disulfide is an important nanomaterial in the field of material chemistry due to its interesting catalytic and electromagnetic properties. We herein report the simple solution phase preparation of nanoparticles of cobalt disulfide in micellar medium of cationic surfactant cetyltrimethylammonium bromide (CTAB) and also by way of capping with thiophenol. The product has been characterized using spectroscopic and electron microscopic and magnetic moment measurements. The presence of disulfide bond is clearly evident from the 480cm−1 peak in the infrared spectrum. The thiol passivated particles prepared in aqueous and ethanol medium has been found to have different compositions as observed from the ESIMS study.
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Truncated rhombic dodecahedral zeolitic imidazolate framework-8 (ZIF-8) nanocrystals are fabricated with acetate as a modulating ligand; ZnS hollow polyhedra with uniform morphology are obtained using the ZIF-8 templates.
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The applications of alloying/dealloying materials as anode for LIB electrode are hindered by its dramatic volume variations and sluggish kinetics. Herein, to overcome these challenges, we report a facile and scalable approach fabricating coral-like SnO2/C composite electrodes through a top-down strategy followed by a sol-gel carbon-coating method. During the synthesis, well-defined SnS2 nanoflowers and dopamine serve as structural template and carbon source for integrating the desired structure. The three-dimensional coral-like SnO2/C composite exhibits a high reversible capacity of 648mAhg-1 after 50 electrochemical cycles and a low capacity fading of 0.778% per cycle from the 2nd to the 50th cycle, demonstrating an outstanding cycling stability. It also shows a discharge capacity of 1294, 784, 658, 532, and 434mAhg-1 at a specific current of 100, 200, 500, 1000 and 2000mAhg-1, respectively, and retains a specific capacity of 719mAhg-1 when the specific current goes back to 100mAg-1, displaying an excellent rate capability. Compared to SnS2 nanoflowers and bare interconnected SnO2 nanoparticles anode, the optimized coral-like SnO2/C composite shows significantly improved electrochemical performances in terms of rate capability and cycling reversibility, demonstrating great potential as superior anodes in next-generation lithium ion batteries.
Article
A series of La-promoted cobalt-copper catalysts with various Co:Cu ratios have been used to study the conversion of syngas to oxygenates and hydrocarbons. In particular, the effect of the Co:Cu composition on the selectivity to oxygenates versus hydrocarbons has been examined. Three bulk catalysts were synthesized by coprecipitation, reduced in H2/He flow, and then cobalt carbide was formed during CO hydrogenation. The composition of the catalysts was as follows: Cu:Co = 12:9, 7:13, and 0:21 (cobalt only). CO hydrogenation tests were performed at differential conversions and 30 bar, H2/CO = 2/1 and 250 °C. The C1 selectivity (methane + methanol + CO2) was ∼64% for the two catalysts containing Co and Cu, and slightly less for the Co-only catalyst (52%). These products are formed by three mechanisms: (1) CH4: hydrogenation of dissociatively adsorbed CO at metallic cobalt sites, (2) CH3OH: hydrogenation of associatively adsorbed CO at copper sites, and (3) CO2: water gas shift, also at the copper sites. C2+ alcohol selectivity for the two Cu-containing catalysts is greater than for the Co-only catalyst, while the Co-only catalyst has the highest selectivity to acetaldehyde. The formation of C2+ oxygenates is consistent with the CO insertion mechanism, in which associatively adsorbed CO is inserted into the CHx species and forms the first C-C bond, producing a CHxCO intermediate that can be hydrogenated into ethanol or acetaldehyde.
Article
A sandwich-like, graphene-based porous nitrogen-doped carbon (PNCs@Gr) has been prepared through facile pyrolysis of zeolitic imidazolate framework nanoparticles in situ grown on graphene oxide (GO) (ZIF-8@GO). Such sandwich-like nanostructure can be used as anode material in lithium ion batteries, exhibiting remarkable capacities, outstanding rate capability, and cycling performances that are some of the best results among carbonaceous electrode materials and exceed most metal oxide-based anode materials derived from metal orgainc frameworks (MOFs). Apart from a high initial capacity of 1378 mAh g(-1) at 100 mA g(-1), this PNCs@Gr electrode can be cycled at high specific currents of 500 and 1000 mA g(-1) with very stable reversible capacities of 1070 and 948 mAh g(-1) to 100 and 200 cycles, respectively. At a higher specific current of 5000 mA g(-1), the electrode still delivers a reversible capacity of over 530 mAh g(-1) after 400 cycles, showing a capacity retention of as high as 84.4%. Such an impressive electrochemical performance is ascribed to the ideal combination of hierarchically porous structure, a highly conductive graphene platform, and high-level nitrogen doping in the sandwich-like PNCs@Gr electrode obtained via in situ synthesis.
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Tin disulfide (SnS2) has been considered as a prospective counter electrode (CE) material for dye-sensitized solar cells due to its good electrocatalytic property. However, its low electronic and ionic conductivities pose challenges for using it in high-performance dye-sensitized solar cells (DSSCs). Herein, doping is utilized in this study to improve the properties of SnS2 for application as the DSSC counter electrode. Ag-doped SnS2 samples with various doping amounts are prepared via a facile one-step solvothermal route. It is found that the DSSC based on 5% Ag-doped SnS2 CE demonstrates the best performance showing an impressive photovoltaic conversion efficiency (PCE) of 8.70 % which exceeds the efficiency of Pt-based DSSC (7.88%) by 10.41%, while the DSSC consisting of undoped SnS2 only exhibits a PCE of 6.47%. Such enhanced efficiency of DSSC is attributed to the effectively improved electrocatalytic activity and mixed conductivity resulted from Ag dopant. Therefore, the Ag-doped SnS2 CE proves a promising alternative to the expensive Pt CE in DSSCs and may pave a new way for large-scale production of new-generation DSSCs.
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Hollow nanostructures with a complex interior and superb structural tenability offer great advantages for constructing advanced catalysts. Herein, we report the designed synthesis of novel Co nanoparticle-embedded carbon@Co9S8 double-shelled nanocages (Co-C@Co9S8 DSNCs) by a metal–organic-framework-engaged strategy. Uniform zeolitic imidazolate framework (ZIF-67)@amorphous CoS yolk–shelled structures are first fabricated and then converted to Co-C@Co9S8 DSNCs by thermal annealing in N2 flow. The Co-C nanocages inside Co9S8 shells function as the active centers for the oxygen reduction reaction (ORR). The Co9S8 shells prevent the Co-C active centers from aggregation while acting as nanoreactors. As a result, the Co-C@Co9S8 DSNCs exhibit excellent performance for the ORR in terms of low over-potential, high current density, excellent stability and methanol tolerance capability.
Article
A hierarchical SnO2@SnS2 core-shell nanostructure has been prepared by in situ surface sulfurization of hollow SnO2 sphere via a facile two-step solution-based method and used as a substitute for conventional Pt counter electrode (CE) for dye-sensitized solar cells (DSSCs) for the first time. The resulted semitransparent SnO2@SnS2 CEs demonstrate a high electrical conductivity and excellent catalytic activity, which are attributed to the synergetic effect of each component in such hierarchical nanostructure. The hierarchical SnO2@SnS2 CE achieves an impressive photovoltaic conversion efficiency (PCE) of 8.08%, which is significantly higher than those of individual SnO2 (5.26%) and SnS2 (6.00%) and also higher than Pt (7.88%) by 2.5%. This study suggests that the inexpensive hierarchical SnO2@SnS2 CE is a good alternative to the expensive Pt CE in DSSCs.
Article
Three cobalt-copper catalysts singly promoted with La, Zr, or Al were studied for catalytic conversion of syngas to higher alcohols. The properties of the promoted catalysts have been characterized by TPR, XRD, XPS and BET. CO hydrogenation was carried out in a plug-flow reactor under 30 bar, GHSV = 36000 scc/gcat/h, H2/CO = 2, and 250 °C at differential conversions. The catalyst activity and selectivity to higher alcohols are greatest on CuCoLa2O3: ethanol selectivity 10.5% at a conversion of 0.76%. During 9 h of time-on-stream, CO conversion decreased on CuCoLa2O3 while methanol and higher alcohol selectivity increased. The behaviors on CuCoZrO2 and CuCoAl2O3 were different. On these two catalysts, CO conversion and selectivity reached a near-steady state much more quickly than CuCoLa2O3. These results suggest changes on CuCoLa2O3 that increase the selectivity for oxygenates continue with time, at least over the time scale investigated here.
Article
Complex hierarchical structures have received tremendous attention due to their superior properties over their constitute components. In this study, hierarchical graphene-encapsulated hollow SnO2@SnS2 nanostructures are successfully prepared by in-situ sulfuration on the backbones of hollow SnO2 spheres via a simple hydrothermal method followed by a solvothermal surface modification. The as-prepared hierarchical SnO2@SnS2@rGO nanocomposite can be used as anode material in lithium ion batteries, exhibiting excellent cycleability with a capacity of 583 mAh/g after 100 electrochemical cycles at a specific current of 200 mA/g. This material shows a very low capacity fading of only 0.273% per cycle from the 2nd to the 100th cycle, lower than the capacity degradation of bare SnO2 hollow spheres (0.830%) and single SnS2 nanosheets (0.393%). Even after being cycled at a range of specific current varied from 2000 mA/g to 100 mA/g, hierarchical SnO2@SnS2@rGO nanocomposite maintains a reversible capacity of 664 mAh/g, which is much higher than single SnS2 nanosheets (374 mAh/g) and bare SnO2 hollow spheres (177 mAh/g). Such significantly improved electrochemical performance can be attributed to the unique hierarchical hollow structure, which not only effectively alleviates the stress resulted from the lithiation/delithiation process and maintains structural stability during cycling but also reduces aggregation and facilitates ion transportation. This work thus demonstrates the great potential of hierarchical SnO2@SnS2@rGO nanocomposites for application as high-performance anode material in next-generation lithium ion battery technology.
Article
In pursuit low-cost and facile synthesis of counter electrode (CE) material as an alternative to expensive Pt for dye-sensitized solar cells (DSSCs), a new procedure for preparing CEs without any postannealing treatment is reported by using a self-assembly technique to obtain a stable thin film as the CE in DSSCs. The self-assembled CoS2 film is prepared via a facile two-step approach, which shows high electrocatalytic activity on the I/I-3 redox reaction. A maximum power conversion efficiency of 6.78% is achieved for the DSSC based on the resultant CoS2 nanocrystal CE, which is close to that of the cell using a Pt CE (7.38%) under the same condition. Moreover, the flexible device based on a CoS2 CE exhibits an efficiency of 6.40%. The results indicate that the self-assembled CoS2 nanoctrystal film may replace the expensive Pt CE for DSSC application, especially for the large-scale flexible devices.
Article
This study reports a novel strategy of preparing CoS2/reduced graphene oxides (RGO) nanocomposites by employing graphene oxides (GO) as an oxidizing agent and Na2S2O3 as a reducing agent. CoS2 can be in situ synthesized with GO being reduced. X-ray diffraction (XRD), Raman spectrometry, scanning electron microscopy (SEM), transmission electron microscopy (TEM) and electrochemical test are used to characterize the nanocomposite. The CoS2 particles with the size of 150 nm are dispersed in the networks made from thin RGO nanosheets. The CoS2/RGO nanocomposite as an anode material for lithium-ion batteries can deliver excellent reversible capacity retention (640 mA hg(-1)) after cycling 50 times when tested at 100 mA g(-1) and rate performance. The enhanced electrochemical properties can be attributed to the nanoscale particles sizes of CoS2 in addition to the effects of RGO networks in preventing the agglomeration of CoS2 and absorbing lithium polysulfides during the charge-discharge processes.
Article
Electrochemical oxygen evolution (OER) and reduction (ORR) reactions have received the great attention due to their importance in several key technologies such as fuel cells, electrolysers and metal-air batteries. Here, we present a simple approach to the preparation of cobalt sulfide nanoparticles in-situ grown on a nitrogen and sulfur co-doped graphene oxide surface. The particle size and phase were controlled by changing the treatment temperature. Cobalt sulfide nanoparticles dispersed on graphene oxide hybrids were successfully prepared by solid state thermolysis approach at different temperatures (400, 500 and 600 ºC) using cobalt thiourea and graphene oxide. X-ray diffraction studies revealed that hybrids prepared at 400 ºC and 500 ºC result in pure CoS2 phase whereas the hybrid prepared at 600 ºC exhibits Co9S8 phase. X-ray photoelectron spectroscopy studies revealed that nitrogen and sulfur simultaneously co-doped on the graphene oxide surface and these sites act to anchor the CoS2 nanoparticles strongly on the GO surface. The strong coupling between CoS2 and N,S-GO was reflected in the improvement of the oxygen electrode potential. CoS2(400)/N,S-GO showed an outstanding oxygen electrode activity with a potential of about 0.82 V against a reversible hydrogen electrode in alkaline medium, which is far better than the performance of precious catalysts such as Pt/C (1.16V), Ru/C (1.01V) and Ir/C (0.92V).
Article
Resurgent interest in iron pyrite (FeS2) as an earth-abundant, non-toxic semiconductor for solar applications has resulted in many attempts to grow phase-pure thin films via chemical vapor deposition (CVD). However, all thin films grown via CVD or sulfidation to date have contained marcasite phase or other iron sulfide impurities. Here, we report the use of metallic cobalt pyrite (cattierite, CoS2) thin films as an ideal substrate leading to the first direct growth of phase-pure iron pyrite thin films via atmospheric pressure CVD. This synthesis was achieved by reacting FeCl3 and di-tert butyl disulfide (TBDS) at 400-450 oC. The products were confirmed as phase-pure iron pyrite using X-ray diffraction (XRD), Raman spectroscopy, and energy dispersive X-ray spectroscopy (EDS). In addition to phase purity, the synthesis produced crystal domains >1 μm and a conformal coating 3-5 μm thick, which are attributed to the <2% lattice mismatch of the isostructural cattierite substrate. The surface was characterized by Ultraviolet and X-ray photoelectron spectroscopy (UPS & XPS) and the electrical properties by electrochemical impedance spectroscopy (EIS) and Mott-Schottky analysis. The direct growth of a phase-pure iron pyrite film on a conductive substrate provides the most convenient configuration so far for potential solar cells.
Article
The dye-sensitized solar cell (DSSC) plays a leading role in third generation photovoltaic devices. Platinum-loaded conducting glass has been widely exploited as the standard counter electrode (CE) for DSSCs. However, the high cost and the rarity of platinum limits its practical application in DSSCs. This has promoted large interest in exploring Pt-free CEs for DSSCs. Very recently, graphene, which is an atomic planar sheet of hexagonally arrayed sp2 carbon atoms, has been demonstrated to be a promising CE material for DSSCs due to its excellent conductivity and high electrocatalytic activity. This article provides a mini review of graphene-based CEs for DSSCs. Firstly, the fabrication and performance of graphene film CE in DSSCs are discussed. Secondly, DSSC counter electrodes made from graphene-based composite materials are evaluated. Finally, a brief outlook is provided on the future development of graphene-based materials as prospective counter electrodes for DSSCs.
Article
To realize long-term developments and practical application of the dye-sensitized solar cells (DSCs) requires a robust increase of the power conversion efficiency (PCE) and a significant decrease of the production cost. Fortunately, a new record PCE value of 12.3% was achieved by using cobalt-based redox couples combined with organic dye. Evidently, dye design is the key path to improve the PCE, while developing low cost counter electrode (CE) catalysts is one of the promising paths to reduce the production cost of DSCs by replacing the expensive Pt CE. In this article, we review the recent progress of CE catalysts involving Pt, carbon materials, inorganic materials, multiple compounds, polymers, and composites. We discuss the advantages and disadvantages of each catalyst and put forward ideas for designing new CE catalysts in future research for DSCs and other application fields.
Article
NiO is an important heterogeneous catalyst employed in chemical processes. However, it is a new topic to explore NiO as a counter electrode catalyst for dye-sensitized solar cells (DSSCs). In this paper, NiO with poly(3,4-ethylenedioxythiophene):polystyrenesulfonate (PEDOT:PSS) was demonstrated an efficient DSSC counter electrode with a maximum power conversion efficiency of 7.58 %. Furthermore, electrochemical impedance spectroscopy and cyclic voltammetry measurements revealed that the excellent photovoltaic performance is due to the combination between the high catalytic activity of NiO and the superior electrical conductivity of PEDOT:PSS. The optimum weight ratio of NiO to PEDOT:PSS is 48.
Article
In the present work, we use chemical exfoliation to fabricate ultrathin two-dimensional anatase TiO2 nanosheets (NSs) for application as photoanode materials in dye-sensitized solar cells. For the first time, colloidal Ti0.91O2 NSs are synthesized via chemical exfoliation of a layered precursor (HxTi2-x/4 square O-x/4(4)center dot H2O; square: vacancy, x = 0.7) through ion exchange with tetrabutylammonium (TBA(+)) cations. The as-prepared Ti0.91O2 NSs are well-dispersed and ultrathin with a lateral size of up to a few micrometers. Subsequent acid treatment induces colloidal Ti0.91O2 to reassemble and precipitate into a gelation form, followed by thermal annealing to convert the Ti0.91O2 gelation into anatase TiO2 nanosheets for applications as photoanode materials in DSSCs. Because of the enhanced light absorption and dye absorption resulting from the high surface area of ultrathin TiO2 nanosheets, the DSSC consisting of 8.8 mu m thick TiO2 nanosheet film delivers the highest energy conversion efficiency of 4.76% and the largest short-circuit current of 9.30 mA cm(-2), among DSSCs based on TiO2 nanosheet films of various thicknesses. It is noted that an overly thick TiO2 NS film will not further increase DSSC efficiency because the thicker layer results in a longer pathway for electron transport and more electron hole recombination. Moreover, a ZrO2 ALD coating combined with TiCl4 treatment on TiO2 NS film can effectively enhance the efficiency of DSSCs to 7.33% by significantly creating more surface area for more dye loading and preventing electron hole recombination between TiO2 and the dye/electrolyte, respectively.
Article
Cobalt disulfide (CoS2)-reduced graphene oxide (RGO) composite (CSG) films, which are prepared by combining the layer by layer assembly method and thermal treatment process, are used as counter electrodes (CEs) for dye-sensitized solar cells (DSSCs). The DSSC with CSG CE exhibits comparable efficiency to the cell with the Pt CE.
Article
Many materials have been explored as potential hydrogen evolution reaction (HER) electrocatalysts to generate clean hydrogen fuel via water electrolysis, but none so far compete with the highly efficient and stable (but cost prohibitive) noble metals. Similarly, noble metals often excel as electrocatalytic counter electrode materials in regenerative liquid-junction photoelectrochemical solar cells, such as quantum dot-sensitized solar cells (QDSSCs) that employ the sulfide/polysulfide redox electrolyte as the hole mediator. Here, we systematically investigate thin films of the earth-abundant pyrite-phase transition metal disulfides (FeS2, CoS2, NiS2, and their alloys) as promising alternative electrocatalysts for both the HER and polysulfide reduction. Their electrocatalytic activity toward the HER is correlated to their composition and morphology. The emergent trends in their performance suggest that cobalt plays an important role in facilitating the HER, with CoS2 exhibiting highest overall performance. Additionally, we demonstrate the high activity of the transition metal pyrites toward polysulfide reduction and highlight the particularly high intrinsic activity of NiS2, which could enable improved QDSSC performance. Furthermore, structural disorder introduced by alloying different transition metal pyrites could increase their areal density of active sites for catalysis, leading to enhanced performance.
Article
Herein, we report synthesis of nitrogen-doped graphene (NGr) interpenetrated 3-D Ni-nanocage (Ni-NGr) electrocatalyst by simple water-in-oil (w/o) emulsion technique for oxidation of water-to-dioxygen. Correlation of adsorption of NGr and subsequent interpenetration through the specific surface plane of nickel particles as well as concomitant interaction of N, C, with Ni at a nano-regime have been investigated. Apart from the benefits of the synergistic interactions between Ni, N, and C, the overall integrity of the structure and its intra-molecular connectivity within the framework help to achieve better oxygen evolution characteristics at a significantly reduced overpotential. The engineered Ni-NGr nanocage displays a substantially low overpotential of ~290 mV at practical current density of 20 mA/cm2 in 0.1 M KOH. In comparison, NGr and Ni-particle as separate entities give overpotentials of ~570 and ~ 370 mV under similar conditions. Moreover, the long term stability of Ni-NGr has been investigated by anodic potential cycling for 500 cycles and observed an 8.5 % increment in the overpotential at 20 mA/cm2. Additionally, chronoamperometric test has been performed for 15 h at 20 mA/cm2, which highlight the better sustainability of Ni-NGr in the actual operating condition. Finally, the quantitative estimation of evolved oxygen has been monitored by gas chromatography and is found to be 70 mmol/h/g of oxygen, which is constant in second cycle as well.
Article
Electrocatalysis plays a key role in the energy conversion processes central to several renewable energy technologies that have been developed to lessen our reliance on fossil fuels. However, the best electrocatalysts for these processes—which include the hydrogen evolution reaction (HER), the oxygen reduction reaction (ORR), and the redox reactions that enable regenerative liquid-junction photoelectrochemical solar cells—often contain scarce and expensive noble metals, substantially limiting the potential for these technologies to compete with fossil fuels. The considerable challenge is to develop robust electrocatalysts composed exclusively of low-cost, earth-abundant elements that exhibit activity comparable to that of the noble metals. In this review, we summarize recent progress in the development of such high-performance earth-abundant inorganic electrocatalysts (and nanostructures thereof), classifying these materials based on their elemental constituents. We then detail the most critical obstacles facing earth-abundant inorganic electrocatalysts and discuss various strategies for further improving their performance. Lastly, we offer our perspectives on the current directions of earth-abundant inorganic electrocatalyst development and suggest pathways toward achieving performance competitive with their noble metal-containing counterparts.
Article
A low-cost, sulfur-doped NiO (S–NiO) thin film is electrodeposited on fluorine-doped SnO2 substrate and studied in an iodide-based redox system. High electrochemical activity is present because of a large catalytic surface area and a low charge transfer resistance. A dye- sensitized solar cell with a low-loaded S–NiO counter electrode achieves a power conversion efficiency of 5.04%, close to that of a cell with a conventional platinized electrode.
Article
A new type of semitransparent SnS2 nanosheet (NS) films were synthesized using a simple and environmentally friendly solution-processed approach, which were subsequently used as a counter electrode (CE) alternative to the noble metal Pt for triiodide reduction in dye-sensitized solar cells (DSSCs). The resultant SnS2 -based CE with a thickness of about 300 nm exhibited excellent electrochemical catalytic activity for catalyzing the reduction of triiodide and demonstrated comparable power conversion efficiency of 7.64 % with that of expensive Pt-based CE in DSSCs (7.71 %). When functionalized with a small amount of carbon nanoparticles, the SnS2 NS-based CE showed even better performance of 8.06 % than Pt under the same conditions. Considering the facile fabrication method, optical transparency, low cost, and remarkable catalytic property, this study on SnS2 NSs may shed light on the large-scale production of electrocatalytic electrode materials for low-cost photovoltaic devices.
Article
The development of efficient and robust earth-abundant electrocatalysts for the hydrogen evolution reaction (HER) is an ongoing challenge. We report metallic cobalt pyrite (cobalt disulfide, CoS2) as one such high-activity candidate material, and demonstrate that its specific morphology-film, microwire, or nanowire, made available through controlled synthesis-plays a crucial role in determining its overall catalytic efficacy. The increase in effective electrode surface area that accompanies CoS2 micro- and nanostructuring substantially boosts its performance, with CoS2 nanowire electrodes achieving geometric current densities of -10 mA cm(-2) at overpotentials as low as -145 mV vs. the reversible hydrogen electrode. Moreover, micro- and nanostructuring of the CoS2 material has the synergistic effect of increasing its operational stability, cyclability, and maximum achievable rate of hydrogen generation by promoting the release of evolved gas bubbles from the electrode surface. The benefits of catalyst micro- and nanostructuring are further demonstrated by the increased electrocatalytic activity of CoS2 nanowire electrodes over planar film electrodes toward polysulfide and triiodide reduction, which suggests a straightforward way to improve the performance of quantum dot- and dye-sensitized solar cells, respectively. Extension of this micro- and nanostructuring strategy to other earth-abundant materials could similarly enable inexpensive electrocatalysts that lack the high intrinsic activity of the noble metals.
Article
Combining quantum-mechanical simulations and synthesis tools allows the design of highly efficient CuCo/MoOx catalysts for the selective conversion of synthesis gas (CO+H2) into ethanol and higher alcohols, which are of eminent interest for the production of platform chemicals from non-petroleum feedstocks. Density functional theory calculations coupled to microkinetic models identify mixed Cu–Co alloy sites, at Co-enriched surfaces, as ideal for the selective production of long-chain alcohols. Accordingly, a versatile synthesis route is developed based on metal nanoparticle exsolution from a molybdate precursor compound whose crystalline structure isomorphically accommodates Cu2+ and Co2+ cations in a wide range of compositions. As revealed by energy-dispersive X-ray nanospectroscopy and temperature-resolved X-ray diffraction, superior mixing of Cu and Co species promotes formation of CuCo alloy nanocrystals after activation, leading to two orders of magnitude higher yield to high alcohols than a benchmark CuCoCr catalyst. Substantiating simulations, the yield to high alcohols is maximized in parallel to the CuCo alloy contribution, for Co-rich surface compositions, for which Cu phase segregation is prevented.