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Construction of a fast, easy and sensitive neurotransmitters-based sensor could provide a promising way for the diagnosis of neurological diseases, leading to the discovery of more effective treatment methods. The current work is directed to develop for the first time a flexible Surface-Enhanced Raman Spectroscopy (SERS) based neurotransmitters sensor by using the ultrasonic-assisted fabrication of a new set of epoxy resin (EPR) nanocomposites based on graphene nanosheets (GNS) using the casting technique. The perspicuous epoxy resin was reinforced by the variable loading of GNS giving the general formula GNS/EPR1-5. The designed products have been fabricated in situ while the perspicuous epoxy resin was formed. The expected nanocomposites have been fabricated using 3%, 5%, 10%, 15% and 20% GNS loading was applied for such fabrication process. The chemical, physical and morphological properties of the prepared nanocomposites were investigated by using Fourier transforms infrared spectroscopy, X-ray diffraction, Thermogravimetric analysis, Differential Thermal gravimetry, and field emission scanning electron microscopy methods. The GNS/EPR1-5 nanocomposites were decorated with a layer of gold nanoparticles (Au NPs/GNS/EPR) to create surface-enhanced Raman scattering hot points. The wettability of the Au NPs/GNS/EPR was investigated in comparison with the different nanocomposites and the bare epoxy. Au NPs/GNS/EPR was used as a SERS-active surface for detecting different concentrations of dopamine with a limit of detection of 3.3 µM. Our sensor showed the capability to detect low concentrations of dopamine either in a buffer system or in human serum as a real sample.
The use of ethanol as a fuel in direct alcohol fuel cells depends not only on its ease of production from renewable sources, but also on overcoming the challenges of storage and transportation. In an ethanol‐based fuel cell, highly active electrocatalysts are required to break the C−C bond in ethanol for its complete oxidation at lower overpotentials, with the aim of increasing the cell performance, ethanol conversion rates, and fuel efficiency. In recent decades, the development of wet‐chemistry methods has stimulated research into catalyst design, reactivity tailoring, and mechanistic investigations, and thus, created great opportunities to achieve efficient oxidation of ethanol. In this Minireview, the nanomaterials tested as electrocatalysts for the ethanol oxidation reaction in acid or alkaline environments are summarized. The focus is mainly on nanomaterials synthesized by using wet‐chemistry methods, with particular attention on the relationship between the chemical and physical characteristics of the catalysts, for example, catalyst composition, morphology, structure, degree of alloying, presence of oxides or supports, and their activity for ethanol electro‐oxidation. As potential alternatives to noble metals, non‐noble‐metal catalysts for ethanol oxidation are also briefly reviewed. Insights into further enhancing the catalytic performance through the design of efficient electrocatalysts are also provided.
Several neurological disorders such as Alzheimer's disease and Parkinson's disease have become a serious impediment to aging people nowadays. One of the efficient methods used to monitor these neurological disorders is the detection of neurotransmitters such as dopamine. Metal materials, such as gold and platinum, are widely used in this electrochemical detection method; however, low sensitivity and linearity at low dopamine concentrations limit the use of these materials. To overcome these limitations, a silver nanoparticle (SNP) modified electrode covered by graphene oxide for the detection of dopamine was newly developed in this study. For the first time, the surface of an indium tin oxide (ITO) electrode was modified using SNPs and graphene oxide sequentially through the electrochemical deposition method. The developed biosensor provided electrochemical signal enhancement at low dopamine concentrations in comparison with previous biosensors. Therefore, our newly developed SNP modified electrode covered by graphene oxide can be used to monitor neurological diseases through electrochemical signal enhancement at low dopamine concentrations.
The detection of dopamine in a highly sensitive and selective manner is crucial for the early diagnosis of a number of neurological diseases/disorders. Here, a report on a new platform for the electrochemical detection of dopamine with a considerable accuracy that comprises a 3D porous graphene oxide (pGO)/gold nanoparticle (GNP)/pGO composite-modified indium tin oxide (ITO) is presented. The pGO was first synthesized and purified by ultrasonication and centrifugation, and it was then further functionalized on the surface of a GNP-immobilized ITO electrode. Remarkably, owing to the synergistic effects of the pGO and GNPs, the 3D pGO-GNP-pGO-modified ITO electrode showed a superior dopamine-detection performance compared with the other pGO- or GNP-modified ITO electrodes. The linear range of the newly developed sensing platform is from 0.1 μM to 30 μM with a limit of detection (LOD) of 1.28 μM, which is more precise than the other previously reported GO-functionalized electrodes. Moreover, the 3D pGO-GNP-pGO-modified ITO electrodes maintained their detection capability even in the presence of several interfering molecules (e.g., ascorbic acid, glucose). The proposed platform of the 3D pGO-GNP-pGO-modified ITO electrode could therefore serve as a competent candidate for the development of a dopamine-sensing platform that is potentially applicable for the early diagnosis of various neurological diseases/disorders.
Supercapacitors, which store electrical energy through reversible ion on the surface of conductive electrodes have gained enormous attention for variously portable energy storage devices. Since the capacitive performance is mainly determined by the structural and electrochemical properties of electrodes, the electrodes become more crucial to higher performance. However, due to the disordered microstructure and low electrochemical activity of electrode for ion tortuous migration and accumulation, the supercapacitors present relatively low capacitance and energy density. Here we report a high-performance supercapacitor based on polyaniline/vertical-aligned carbon nanotubes (PANI/VA-CNTs) nanocomposite electrodes where the vertical-aligned-structure is formed by the electrochemical-induction (0.75 V). The supercapacitor displays large specific capacitance of 403.3 F g−1, which is 6 times higher than disordered CNTs in HClO4 electrolyte. Additionally, the supercapacitor can also present high specific capacitance (314.6 F g−1), excellent cycling stability (90.2% retention after 3000 cycles at 4 A g−1) and high energy density (98.1 Wh kg−1) in EMIBF4 organic electrolyte. The key to high-performance lies in the vertical-aligned-structure providing direct path channel for ion faster diffusion and high electrochemical capacitance of polyaniline for ion more accommodation.
A simple method is demonstrated to prepare spongy adenine-functionalized graphene (SFG) as interconnected, porous 3-dimensional (3D) network crinkly sheets. Such 3D network structure provides better contact at the electrode/electrolyte interface and facilitates the charge transfer kinetics. The fabricated SFG was characterized by X-ray diffraction (XRD), FTIR, scanning electron microscopy (FESEM), Raman spectroscopy, thermogravimetric analysis (TGA), UV−vis absorption spectroscopy, and transmission electron microscopy (TEM). The synthesized materials have been evaluated as supercapacitor materials in 0.5 M H2SO4 using cyclic voltammetry (CV) at different potential scan rates, and galvanostatic charge/discharge tests at different current densities. The SFG electrodes showed a maximum specific capacitance of 333 F/g at scan rate of 1 mV/s and exhibited excellent cycling retention of 102% after 1000 cycles at 200 mV/s. The energy density was 64.42 Wh/kg with a power density of 599.8 W/kg at 1.0 A/g. Those figures of merit are much higher than those reported for graphene-based materials tested under similar conditions. The observed high performance can be related to the synergistic effects of the spongy structure and the adenine functionalization.
One-dimensional (1D) anisotropic Pt-based nanowires are promising electrocatalysts in polymer electrolyte membrane fuel cells owing to the inherent structural merits. Herein, we report an in-situ growth of ultrathin PtRh nanowires (diameters 2~3 nm) on graphene nanosheets via the oriented attachment pathway. Mechanistic studies reveal that graphene nanosheets play a critical role in the nucleation and growth of PtRh nanowires. The resulting hybrid of PtRh nanowires decorated graphene nanosheets shows outstanding activity and durability toward ethanol electro-oxidation. It exhibits a specific current density of 2.8 mA cm-2 and a mass-normalized current density of 1 A mg-1 metal, which are 5.4 and 3.1 times of those of state-of-the-art Pt/C catalyst, respectively. After 2000 cyclic tests, it maintains 86% of the initial electrochemical active surface area, which is larger than that of 63% obtained from the Pt/C catalyst. The superior performance is attributed to the combination of the advantageous 1D morphological motif with the synergistic effects of PtRh alloys and graphene nanosheet support.
A perfect ultra-narrow band infrared metamaterial absorber based on the all-metal-grating structure is proposed. The absorber presents a perfect absorption efficiency of over 98% with an ultra-narrow bandwidth of 0.66 nm at normal incidence. This high efficient absorption is contributed to the surface plasmon resonance. Moreover, the surface plasmon resonance-induced strong surface electric field enhancement is favorable for application in biosensing system. When operated as a plasmonic refractive index sensor, the ultra-narrow band absorber has a wavelength sensitivity 2400 nm/RIU and an ultra-high figure of merit 3640, which are much better than those of most reported similar plasmonic sensors. Besides, we also comprehensively investigate the influences of structural parameters on the sensing properties. Due to the simplicity of its geometry structure and its easiness to be fabricated, the proposed high figure of merit and sensitivity sensor indicates a competitive candidate for applications in sensing or detecting fields.
Biosynthesis based on the reducing capacity of electrochemically active bacteria is frequently used in the reduction of metal ions into nanoparticles as an eco-friendly way to recycle metal resources. However, those bionanoparticles cannot be used directly as electrocatalysts because of the poor conductivity of cell substrates. This problem was solved by a hydrothermal reaction, which also contributes to the heteroatom doping and alloying between Pd and Au. With the protection of graphene, the aggregation of nanoparticles was successfully avoided, and the porous structure was maintained, resulting in better electrocatalytic activity and durability than commercial Pd/C under both alkaline (CH3CH2OH, 6.15-fold of mass activity) and acidic (HCOOH, 6.58-fold of mass activity) conditions. The strategy developed in this work opens up a horizon into designing electrocatalysts through fully utilizing the abundant resources in nature.
There is no doubt that, epoxy resin is one of the most important materials that has been widely used in coating technology. The present work is aimed to fabricate a new series of epoxy resin nanocomposites in the form of G/CNTs/EPY 1-4 using simple dissolution method and ultrasonic assistance. The expected nanocomposites have been fabricated using 10% loading of different mixed ratios from G/CNTs. Four different G/CNTs mixed ratios were used 20/80%, 40/60%, 60/40%, and 80/20%. The structure of the G/CNT/EPY 1-4 nanocomposites has been investigated and confirmed by normal characterization techniques including: X-ray diffraction (XRD), Fourier transforms infrared spectroscopy (FT-IR), Thermogravimetric analysis (TGA), Differential Thermal gravimetry (DTG) and field emission scanning electron microscopy (FE-SEM). T 25 and T 50 values for G/CNT/EPY 1-4 nanocomposites were slightly higher than elegant epoxy. R 500 values for the fabricated materials were in the range of 8.98 – 10.04 %. Furthermore, the role of mixed G/CNTs on the coating properties of epoxy resin was determined using electrochemical impedance and technique. The coating resistance of epoxy composites in the form of G/CNT/EPY 1-4 was larger than that observed for elegant epoxy coating. G/CNT/EPY 3 and G/CNT/EPY 1 showed highest and the lowest coating impedance values respectively. In addition to that, the water sorption technique has been used as a complementary method for such coating behaviour. The water uptake was efficiently decreased in all the formulations compared to the epoxy due to the presence of G/CNTs reinforcing agents.
This mini-review highlights selectively the recent research progress in the composites of LiFePO4 and graphene. In particularly, the different fabrication protocols, and the electrochemical performance of the composites are summarized in detail. The structural and morphology characters of graphene sheets that may affect the property of the composites are discussed briefly. The possible ongoing researches in area are speculated upon.
Multidisciplinary, innovative and high values development of high performance, cost-effective and environmentally acceptable separation systems is highly desired to tackle the sustainability challenges that facing current desalination technology. Owing to their versatility and immense potentials to evolve scientific and technical innovations, nanotechnology is probably one of the most prominent strategies that has gained growing scientific and public recognition to provide solutions that can extend the limits of sustainability in membrane desalination technology. This short review provides a brief insight into the roles and prospective of nanotechnology, particularly the nano-enabled membrane technology, to serve as a key element to render feasible solutions for sustainable development in membrane desalination technology. The contribution also highlights the strategies of transforming risk and challenges of this cutting edge technology into competitive advantage in order to timely and efficiently drive values in enhancing the desalination performance, profits and sustainability. The applications of nanomaterials and nanocomposite in membrane desalination are anticipated to foster untapped initiatives and innovation in fundamental science, engineering and technology to spearhead the new wave of leading edge sustainable membrane desalination technology.
Transparent conductive film on plastic substrate is a critical component in low-cost, flexible and lightweight optoelectronics. Industrial-scale manufacturing of high-performance transparent conductive flexible plastic is needed to enable wide-ranging applications. Here, we demonstrate a continuous roll-to-roll (R2R) production of transparent conductive flexible plastic based on a metal nanowire network fully encapsulated between graphene monolayer and plastic substrate. Large-area graphene film grown on Cu foil via a R2R chemical vapor deposition process was hot-laminated onto nanowires pre-coated EVA/PET film, followed by a R2R electrochemical delamination which preserves the Cu foil for reuse. The encapsulated structure minimized the resistance of both wire-to-wire junctions and graphene grain boundaries, strengthened adhesion of nanowires and graphene to plastic substrate, resulting in superior optoelectronic properties (sheet resistance of ~8 ohm/sq at 94 % transmittance), remarkable corrosion resistance and excellent mechanical flexibility. With these advantages, long-cycle life flexible electrochromic devices are demonstrated, showing up to 10000 cycles.
Interest in two-dimensional, sheet-like or flake-like carbon forms has expanded beyond monolayer graphene to include related materials with significant variations in layer number, lateral dimension, rotational faulting, and chemical modification. Describing this family of "graphene materials" has been causing confusion in the Carbon journal and in the scientific literature as a whole. The international editorial team for Carbon believes that the time has come for a discussion on a rational naming system for two-dimensional carbon forms. We propose here a first nomenclature for two-dimensional carbons that could guide authors toward a more precise description of their subject materials, and could allow the field to move forward with a higher degree of common understanding.
There is an increasing worldwide demand for high energy density batteries. In recent years, rechargeable Li-ion batteries have become important power sources, and their performance gains are driving the adoption of electrical vehicles (EV) as viable alternatives to combustion engines. The exploration of new Li-ion battery materials is an important focus of materials scientists and computational physicists and chemists throughout the world. The practical applications of Li-ion batteries and emerging alternatives may not be limited to portable electronic devices and circumventing hurdles that include range anxiety and safety among others, to their widespread adoption in EV applications in the future requires new electrode materials and a fuller understanding of how the materials and the electrolyte chemistries behave. Since this field is advancing rapidly and attracting an increasing number of researchers, it is crucial to summarise the current progress and the key scientific challenges related to Li-ion batteries from theoretical point of view. Computational prediction of ideal compounds is the focus of several large consortia, and a leading methodology in designing materials and electrolytes optimized for function, including those for Li-ion batteries. In this Perspective, we review the key aspects of Li-ion batteries from theoretical perspectives: the working principles of Li-ion batteries, the cathodes, anodes, and electrolyte solutions that are the current state of the art, and future research directions for advanced Li-ion batteries based on computational materials and electrolyte design.
Graphene synthesized via chemical vapor deposition is a notable candidate for flexible large-area transparent electrodes due to its great physical properties and its 2D activated surface area. Electrochromic devices in optical displays, smart windows, etc are suitable applications for graphene when used as a transparent conductive electrode. In this study, various-layer graphene was synthesized via chemical vapor deposition, and inorganic WOx was deposited on the layers, which have advantageous columnar structures and W6+ and W4+ oxidation states. The characteristics of graphene and WOx were verified using optical transmittance, Raman spectroscopy, x-ray photoelectron spectroscopy and scanning electron microscopy. The optimum transparent conductive electrode condition for controlling graphene layers was investigated based on the optical density and cyclic voltammetry. Electrochromic devices were fabricated using a three-layer graphene electrode, which had the best optical density. The graphene in the flexible electrochromic device demonstrated a potential for replacing ITO in flexible electronics.
How the fuel cells could be performed in a cold climate is an enormous challenge for widespread applications, which is highly related to the construction of efficient low-temperature electrocatalysts with stabilizer/surfactant-free clean surface. Herein, ultra-clean and monodisperse PtPd nanoflowers (NFs) deposited on graphene oxide (GO) were successfully synthesized via a modified in-situ overgrowth strategy by adding ethanol as an efficient booster in the redox reaction between GO and metallic precursors. As for methanol oxidation reaction (MOR), the resulting GO/PtPd NFs provide much higher electrocatalytic performances (mass and specific activity as well as long-term durability) than the loading of monometallic Pt or Pd nanoparticles on the GO support. Especially, compared to MOR test at room temperature (25 °C), 70% electrocatalytic activity of GO/PtPd NFs can be maintained even under low temperature (5 °C) condition, while that of commercial Pt/C catalysts is merely about 57%. The unique product with enhanced low-temperature electrocatalytic activity holds great potential for promoting the utilization of fuel cells in grimly cold weather condition.
The design and construction of high-performance platinum-based electrode catalysts with acceptable cost are the keys to advances in the field of direct methanol fuel cells (DMFCs). Herein, we report an efficient bottom-up approach to the large-scale production of ultrafine Pt nanoparticle-decorated 3D hybrid architectures by employing graphene (RGO) and MXene (Ti3C2Tx) nanosheets as co-building blocks. Benefiting from their distinct structural merits, such as highly interconnected porous carbon networks, large specific surface areas, homogeneous metallic Pt dispersion, and good electron conductivity, the resulting 3D Pt/RGO-Ti3C2Tx architectures express surprisingly high catalytic activity, reliable long-term stability, and strong poison tolerance as they are utilized as anode DMFC catalysts, which are more competitive than those for conventional Pt catalysts supported by carbon black, carbon nanotube, RGO, and Ti3C2Tx materials. Density functional theory calculation further reveals an optimized band structure of the reduced graphene oxide-Ti3C2Tx support as well as its strong electronic interactions with Pt nanoparticles, which are essential for the exceptional electrocatalytic properties toward methanol oxidation reaction.
Various types of fuel cells as clean and portable power sources show a great attraction, especially direct methanol fuel cells (DMFCs) having high energy density and convenient fuel storage. In this paper, PtNi bimetallic nanoparticles (NPs) supported on the electrochemically reduced porous graphene oxide (ERPGO) was fabricated by one-step electrochemical reduction of the mixture of H2PtCl6, NiSO4 and porous graphene oxide (PGO). The obtained hybrid of PtNi/ERPGO was investigated by using scanning electron microscopy (SEM), X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS). Furthermore, the electrocatalytic activity for methanol oxidation reaction (MOR) was evaluated by electrochemical method. The experimental results have demonstrated that PtNi/ERPGO enhanced electrocatalytic activity, which might be attributed to the bifunctional mechanism and the existence of unique pore structure on the surface of graphene sheets.
High-efficient electrocatalysis for clean, efficient and sustainable energy supply, such as hydrogen evolution reaction (HER) and formic acid oxidation reaction (FAOR), has drawn enthusiastic and worldwide attention. Universal and efficient electrocatalysts for these reactions are essential elements for the development of renewable and clean energy technologies. Herein, we show the design and fabrication of the rhodium nanoparticles modified fluorine-doped graphene (Rh/F-graphene) catalyst using silicon nanowires (SiNWs) as the sacrifice template. The optimized Rh/F-graphene catalyst (Rh/F-graphene-2) has a low Rh mass fraction of 9.4% and F doping of 4.0%. The mean diameter of Rh is 9.39 nm. Rh/F-graphene-2 serves as a proton-adsorption-dominated multifunctional electrocatalyst for both HER and FAOR with performance superior to 20 wt% Pt/C in acidic solution. In addition, due to the doping of fluorine, the stability of Rh/F-graphene-2 catalyst greatly improves and is the best among all the compared electrocatalysts. This design for multifunctional catalysts could greatly increase the utilization ratio of Rh, which may provide a new avenue for the preparation of other noble metal-based catalysts.
Although direct methanol fuel cell presents a huge potential of application in the modern society, the lack of high-efficiency anode catalysts with acceptable cost has largely hindered its large-scale commercialization. Here, we demonstrate a bottom-up approach to the fabrication of ultrafine Pt nanoparticles dispersed on 3D low-defect carbon nanotube/nitrogen-doped graphene hybrid aerogel (Pt/LDCNT-NG) via a convenient and cost-effective self-assembly process. Both experiments and theoretical calculations reveal that the rationally assembled 3D Pt/LDCNT-NG architectures possess low defect density, optimized electronic structure, and enhanced Pt stability, thus giving them high electrocatalytic activity as well as long lifespan toward methanol oxidation reaction, which far outperforms those for conventional Pt/carbon black, Pt/acid-treated CNT, Pt/graphene, and Pt/nitrogen-doped graphene catalysts. It is anticipated that the synthetic strategy presented here can be further extended to the construction of various 3D heteroatom-doped low-defect carbonaceous nanomaterials that contains metals or metal oxides, which are conducive to the development of high-performance energy storage and conversion devices.
The design of novel platinum-free highly efficient electrocatalysts for the oxygen reduction reaction (ORR) and methanol oxidation reaction (MOR) has been regarded as the core challenge toward the development of commercially available fuel cell devices. In this contribution, a facile strategy was applied to prepare surfactant-free nickel-core palladium-shell nanoparticles, abbreviated as Pd@NiNPs, uniformly distributed on sulfur-doped graphene (SG). The Pd@NiNPs/SG hybrid material was realized by employing a modified polyol method for the in-situ preparation of NiNPs/SG, followed by deposition of a Pd shell through the galvanic replacement method and complementary characterized by Raman and IR spectroscopy, STEM/EELS, SEM and EDS as well as XRD and TGA. The Pd-to-Ni molar ratio was optimized in view of the hybrid’s electrocatalytic performance. Interestingly, the Pd@NiNPs/SG hybrid was proved to be a highly efficient and stable electrocatalyst towards ORR and MOR. It exhibited comparable initial ORR performance with the benchmark Pd/C catalyst and importantly greater stability, as after 2,000 potential cycles it possesses 36% and 67% higher diffusion-limited and kinetic current density, respectively, having a minimal loss of its initial activity. Further investigations on the reaction kinetics showed a 4-electron direct reduction of oxygen to water for the Pd@NiNPs/SG as well as Tafel slopes of -48/-116 mV dec-1, values much close to those proposed for the polycrystalline platinum. In addition, Pd@NiNPs/SG revealed enhanced MOR specific activity by 82% over Pd/C (2.26 mA cm-2 vs. 1.24 mA cm-2) and by far better anti-poisoning abilities. Overall, Pd@NiNPs/SG hybrid is a highly efficient and low cost electrocatalyst, revealing huge potential for application in high-performance energy conversion devices.
Although electrocatalytic hydrogen evolution and methanol oxidation have long been regarded as promising technologies for future energy production and conversion, the incapability of the electrode catalysts poses a major impediment to their large-scale commercialization. Herein, we present a facile co-assembly approach to the fabrication of Pt nanocrystals grown on 3D architectures built from ultrathin graphene and MoS2 nanosheets. By virtue of their unique textural features, such as large specific surface area, 3D cross-linked porous framework, homogeneous distribution of Pt nanoparticles, and excellent electron conductivity, the resulting Pt/graphene-MoS2 architectures possess multifunctional catalytic activities toward hydrogen evolution and methanol oxidation reactions, accompanied by high durability and strong poison tolerance, which significantly outperform those for conventional Pt/carbon black, Pt/graphene, and Pt/MoS2 catalysts. It is believed that such a simple bottom-up design concept can open up new possibilities for the up-scale synthesis of various 3D hybrid architectures with metals or metal oxides for energy-related applications.
Two dimensional (2D) graphene nanosheets are considered as an attractive support to load metal nanoparticles for applications in fuel cells due to their extraordinary physicochemical properties arising from the 2D nanostructure. However, fabricating graphene/metal nanoparticle nanohybrids with superior electrochemical performance remains a great challenge to date. In this manuscript, we, for the first time, demonstrate a novel and ingenious approach to fabricate holey reduced graphene oxide hollow nanospheres sandwiched by interior and exterior Pt nanoparticles (denoted as Pt@holey r-GO@Pt hollow nanospheres), using uniform SiO2 nanospheres as the templates. The Pt@holey r-GO@Pt hollow nanospheres represent a new type of metal/graphene heteroarchitecture due to their rich porosity, abundant active sites, facilitated reaction kinetics and outstanding structural stability. Thanks to these distinguished merits, the as-prepared Pt@holey r-GO@Pt hollow nanospheres exhibit greatly enhanced electrocatalytic performances toward the oxygen reduction reaction (ORR) and methanol oxidation reaction (MOR) as compared with the intact counterparts and commercial Pt/C catalyst, showing great potential in fuel cell devices. The smart strategy outlined here should be readily applicable to rational design of other graphene/metal nanoparticle nanohybrids for energy storage and conversion applications in the future.
Pure Ni nanoparticles with ultrafine size (2.3 ± 0.4 nm) embedded on rGO, present ultrahigh catalytic activity (1600 mA/mg), excellent stability (1020 mA/mg retained after 1000 cycles), and a saturation...
Herein, a one-pot wet-chemical route was used to prepare well-defined dendritic core-shell gold@gold-palladium nanoflowers supported on reduced graphene oxide (Au@AuPd NFs/rGO), using 2, 4-dihydroxypyridine (2, 4-DHP) asa new stabilizer and structure-director. Their morphology, size, composition, and crystal structure were characterized by a set of characterization techniques. Control experiments demonstrated that the molar ratio of the metal precursors and the dosage of 2,4-DHP play essential roles in this synthesis. The growth mechanism of dendritic core-shell Au@AuPd nanoflowers was investigated in details. The synthesized branched architectures exhibited enlarged electrochemically active surface area (ECSA), improved catalytic properties, enhanced stability and durability toward glycerol oxidation in alkaline media when compared to the home-made Au26Pd74 nanocrystals (NCs)/rGO and Au78Pd22 NCs/rGO, along with commercially available Pd/C catalyst.
Most electrocatalysts for the ethanol oxidation reaction suffer from extremely limited operational durability and poor selectivity toward the CC bond cleavage. In spite of tremendous efforts over the past several decades, little progress has been made in this regard. This study reports the remarkable promoting effect of Ni(OH)2 on Pd nanocrystals for electrocatalytic ethanol oxidation reaction in alkaline solution. A hybrid electrocatalyst consisting of intimately mixed nanosized Pd particles, defective Ni(OH)2 nanoflakes, and a graphene support is prepared via a two-step solution method. The optimal product exhibits a high mass-specific peak current of >1500 mA mg−1Pd, and excellent operational durability forms both cycling and chronoamperometric measurements in alkaline solution. Most impressively, this hybrid catalyst retains a mass-specific current of 440 mA mg−1 even after 20 000 s of chronoamperometric testing, and its original activity can be regenerated via simple cyclic voltammetry cycles in clean KOH. This great catalyst durability is understood based on both CO stripping and in situ attenuated total reflection infrared experiments suggesting that the presence of Ni(OH)2 alleviates the poisoning of Pd nanocrystals by carbonaceous intermediates. The incorporation of Ni(OH)2 also markedly shifts the reaction selectivity from the originally predominant C2 pathway toward the more desirable C1 pathway, even at room temperature.
Graphene paper shows a great promise for the electrical energy storage. However, the high stability, purity and specific surface area have become stringent requirements for supercapacitor applications. Finding methods to tackle these problems is rather challenging. Here, we develop a facile method to prepare porous graphene papers with a thickness 0.5 mm by a thermal shock to the layer-structure graphene paper self-assembled on Cu foil under nitrogen flowing. The as-prepared porous graphene paper exhibits a large specific capacitance of 100 F g⁻¹ at the scan rate of 100 mV s⁻¹ with high stability and purity without any residual chemical reagents, showing a promising potential for supercapacitor applications. The high electrochemical properties are mainly attributed to the high-specific area and the improved conductivity of the porous graphene paper performed by the multieffect of reducing, cleaving and expanding to the layer-structure graphene paper by high-energy thermal heating during the thermal shock process. This work paves a pathway to the facile preparation of porous graphene paper for supercapacitor applications.
High energy density Li-ion batteries have attracted broad attention due to their great significance for various applications ranging from portable electronics to electric vehicles. However, emerging applications require batteries with greater than currently available energy densities, which have motivated numerous research efforts such as investigations on high energy density active materials, and engineered electrode structures that maximize the capacity. Three-dimensional (3D) graphene provides promising pathways for developing high energy density electrodes including cathodes and anodes, because of its potential for providing a conductive 3D network, improving Li⁺ ion and electron transfer, as well as accommodating the structure and volume change during cycling. In this review, recent research efforts particularly focused on 3D graphene-based nanocomposite electrodes which exhibit high energy density, high capacity, and good rate performance have been summarized comprehensively. The current challenges for high energy density Li-ion batteries have been discussed, while the potential research perspectives have been presented as well, which we hope would inspire high-performance battery investigations.
A deterministic graphene-sandwiched Li-ion battery electrode consisting of an integrated 3D mesostructure of electrochemically active materials and graphene is presented. As demonstrations, electrodes with active nanomaterials that coat (V2 O5 @graphene@V2 O5 cathode) or are coated by (graphene@Si@graphene anode) graphene are fabricated. These electrodes exhibit high capacities and ultralong cycle lives (the cathode can be cycled over 2000 times with minimal capacity fade).
Electrochemical capacitors, also called supercapacitors, store energy using either ion adsorption (electrochemical double layer capacitors) or fast surface redox reactions (pseudo-capacitors). They can complement or replace batteries in electrical energy storage and harvesting applications, when high power delivery or uptake is needed. A notable improvement in performance has been achieved through recent advances in understanding charge storage mechanisms and the development of advanced nanostructured materials. The discovery that ion desolvation occurs in pores smaller than the solvated ions has led to higher capacitance for electrochemical double layer capacitors using carbon electrodes with subnanometre pores, and opened the door to designing high-energy density devices using a variety of electrolytes. Combination of pseudo-capacitive nanomaterials, including oxides, nitrides and polymers, with the latest generation of nanostructured lithium electrodes has brought the energy density of electrochemical capacitors closer to that of batteries. The use of carbon nanotubes has further advanced micro-electrochemical capacitors, enabling fl exible and adaptable devices to be made. Mathematical modelling and simulation will be the key to success in designing tomorrow's high-energy and high-power devices. © 2010 Nature Publishing Group, a division of Macmillan Publishers Limited and published by World Scientific Publishing Co. under licence. All Rights Reserved.
Graphene has been regarded as a promising candidate for a new generation of transparent electrodes (TEs) due to its prominent characteristics including high optical transmittance, exceptional electronic transport, outstanding mechanical strength, and environmental stability. Comprehensive and critical insights into the latest advances in graphene-based TEs (GTEs) since, but not limited to 2013, are provided, with an emphasis on fabrication, modification, and versatile applications. Several emerging application areas not previously summarized, including electrochromic devices, supercapacitors, electrochemical and electrochemiluminescent sensors, are discussed in detail. The challenges and prospects in these fields are also addressed.
A silver nanoparticles modified carbon paste electrode (MCPE) was developed for the detection of dopamine using voltammetric techniques. The silver nanoparticles (AgNPs) were synthesized through a biological method by using leaf extract act as a reducing agent. The prepared AgNPs were characterized by X-ray diffraction (XRD) and UV–visible absorption spectroscopy (UV–vis). AgNPs are ideally suited for implementation in electrochemical applications due to their high electrical conductivity, high heterogeneous electron transfer rate, and low production cost. The electrochemical response of dopamine at a MCPE prepared with AgNPs is compared with the response of surfactant assisted synthesized AgNPs (S-AgNPs). The effect of pH suggests that an equal number of protons and electrons are involved in the electrochemical oxidation of dopamine. Differential pulse voltammetric technique (DPV) was used for the simultaneous determination of dopamine (DA), ascorbic acid (AA) and uric acid (UA). The peak potential separations for DA-AA and DA-UA were about 181 mV and 168 mV respectively, and the detection limit was 0.085 μM for DA. This work presents a simple approach to the determination of DA in the presence of AA and UA.
High performance of electrocatalysts for direct methanol fuel cells was demonstrated by three-dimensional (3D) graphene (GR) decorated with platinum (Pt)-gold (Au) alloy nanoparticles (3D-GR/PtAu). The 3D-GR/PtAu composite with a morphology like a crumpled paper ball was synthesized from a colloidal mixture of GR and Pt-Au alloy nanoparticles with aerosol spray drying. The 3D-GR/PtAu had a high specific surface area and electrochemical surface area of up to 238 and 325 m2/g(Pt), respectively, and the electrocatalytic applications of the 3D-GR/PtAu were examined through methanol oxidation reactions. The 3D-GR/PtAu had the highest electrocatalytic activity for methanol oxidation reactions compared with commercial Pt-carbon black and Pt-GR. The 3D-GR/PtAu was also highly sensitive electrocatalytic activity in the methanol oxidation reaction compared with the 2D-GR/Pt-Au. Furthermore, the electrocatalytic activity of the 3D-GR/PtAu had the highest performance among the catalysts containing Pt, Au, and GR for the methanol oxidation reactions. The increased electrocatalytic activity is attributed to the high specific surface area of the 3D formation and the effective surface structure of the Pt-Au alloy nanoparticles.
A simple process for preparing 3D structured graphene (3D-G) by a solution combustion method is reported. The product was deposited with platinum and used for methanol electrooxidation. The catalyst shows considerable enhancement on both activity and stability towards methanol electrooxidation reaction. Characterizations reveal that the Pt/3D-G catalyst has a more negative onset potential as well as a higher electrochemically active specific surface area compared with a commercial Pt/C catalyst. Moreover, the catalyst exhibits higher tolerance to corrosion than carbon black. This work provides an efficient way for preparing 3D-G as a promising support for the oxidation of small organic molecules in fuel cells.
Transparency has never been integrated into freestanding flexible graphene paper (FF-GP), although FF-GP has been discussed extensively, because a thin transparent graphene sheet will fracture easily when the template or substrate is removed using traditional methods. Here, transparent FF-GP (FFT-GP) was developed using NaCl as the template and was applied in transparent and stretchable supercapacitors. The capacitance was improved by nearly 1000-fold compared with that of the laminated or wrinkled chemical vapor deposition graphene-film-based supercapacitors.
In this paper, a review of emerging desalination technologies is presented. Several technologies for desalination of municipal and industrial wastewater have been proposed and evaluated, but only certain technologies have been commercialized or are close to commercialization. This review consists of membrane-based, thermal-based and alternative technologies. Membranes based on incorporation of nanoparticles, carbon nanotubes or graphene-based ones show promise as innovative desalination technologies with superior performance in terms of water permeability and salt rejection. However, only nanocomposite membranes have been commercialized while others are still under fundamental developmental stages. Among the thermal-based technologies, membrane distillation and adsorption desalination show the most promise for enhanced performance with the availability of a waste heat source. Several alternative technologies have also been developed recently; those based on capacitive deionization have shown considerable improvements in their salt removal capacity and feed water recovery. In the same category, microbial desalination cells have been shown to desalinate high salinity water without any external energy source, but to date, scale up of the process has not been methodically evaluated. In this paper, advantages and drawbacks of each technology is discussed along with a comparison of performance, water quality and energy consumption.
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The aim of the contribution is to introduce a high performance anode alternative to graphite for lithium-ion batteries (LiBs). A simple process was employed to synthesize uniform graphene-like few-layer tungsten sulfide (WS2) supported on reduced graphene oxide (RGO) through a hydrothermal synthesis route. The WS2–RGO (80:20 and 70:30) composites exhibited good enhanced electrochemical performance and excellent rate capability performance when used as anode materials for lithium-ion batteries. The specific capacity of the WS2–RGO composite delivered a capacity of 400–450 mAh g−1 after 50 cycles when cycled at a current density of 100 mA g−1. At 4000 mA g−1, the composites showed a stable capacity of approximately 180–240 mAh g−1, respectively. The noteworthy electrochemical performance of the composite is not additive, rather it is synergistic in the sense that the electrochemical performance is much superior compared to both WS2 and RGO. As the observed lithiation/delithiation for WS2–RGO is at a voltage≈1.0 V (≈0.1 V for graphite, Li+/Li), the lithium-ion battery with WS2–RGO is expected to possess high interface stability, safety and management of electrical energy is expected to be more efficient and economic.
A three-dimensional Au nanoparticles/graphene/carbon fibers hybrid electrode was fabricated by a layer-by-layer method, denoted as Au0.5/RGO/Au0.5/RGO/CF. The as-formed composite was characterized by Raman spectroscopy, X-ray diffraction (XRD), scanning electron microscope (SEM) and X-ray photoelectron spectroscopy (XPS). It was found that two layers of reduced graphene oxide (RGO) sheets and two layers of Au nanoparticles were assembled alternately on carbon fibers. The catalytic performances of as-prepared electrode were evaluated via the cyclic voltammetry (CV) and chronopotentiometry (CA) measurements. It was demonstrated that the as-synthesized 3D Au0.5/RGO/Au0.5/RGO/CF electrode exhibited highly efficient electrocatalytic activity toward ethanol oxidation in alkaline medium and Au NPs was not affected by the covered graphene layers. The synergetic interaction between RGO sheets and Au nanoparticles enhanced the catalytic activity of the electrode. Meanwhile, the excellent electron conductivity of RGO sheets benefited to the electron transfer and the oxidation removal of the intermediate species during the ethanol electrooxidation, which was good to the catalytic activity. Because of the effects of the above multiple factors, the Au0.5/RGO/Au0.5/RGO/CF electrode exhibited well catalytic performances.
As a potential solution to concerns on sustainable energy, the wide spread commercialization of fuel cell has long been hindered by limited reserves and relatively high costs of metal catalysts. 3D graphene, a carbon-only catalyst prepared by reduction of carbon monoxide with lithium oxide, is found to electrochemically catalyze carbohydrazide oxidation reaction efficiently. A prototype of a completely metal-catalyst-free anion exchange membrane fuel cell (AEMFC) with a 3D graphene anode catalyst and an N-doped CNT (N-CNT) cathode catalyst generate a peak power density of 24.9 mW cm(-2) . The average number of electrons electrochemically extracted from one carbohydrazide molecule is 4.9, indicating the existence of CN bond activation, which is a key factor contributing to high fuel utilization efficiency.
© 2014 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.
The piezoelectric characteristics of nanowires, thin films and bulk crystals have been closely studied for potential applications in sensors, transducers, energy conversion and electronics. With their high crystallinity and ability to withstand enormous strain, two-dimensional materials are of great interest as high-performance piezoelectric materials. Monolayer MoS2 is predicted to be strongly piezoelectric, an effect that disappears in the bulk owing to the opposite orientations of adjacent atomic layers. Here we report the first experimental study of the piezoelectric properties of two-dimensional MoS2 and show that cyclic stretching and releasing of thin MoS2 flakes with an odd number of atomic layers produces oscillating piezoelectric voltage and current outputs, whereas no output is observed for flakes with an even number of layers. A single monolayer flake strained by 0.53% generates a peak output of 15 mV and 20 pA, corresponding to a power density of 2 mW m(-2) and a 5.08% mechanical-to-electrical energy conversion efficiency. In agreement with theoretical predictions, the output increases with decreasing thickness and reverses sign when the strain direction is rotated by 90°. Transport measurements show a strong piezotronic effect in single-layer MoS2, but not in bilayer and bulk MoS2. The coupling between piezoelectricity and semiconducting properties in two-dimensional nanomaterials may enable the development of applications in powering nanodevices, adaptive bioprobes and tunable/stretchable electronics/optoelectronics.
Schottky barriers formed by graphene (monolayer, bilayer, and multilayer) on 2D layered semiconductor tungsten disulfide (WS2) nanosheets are explored for solar energy harvesting. The characteristics of graphene-WS2 junction varies significantly with the number of graphene layers on WS2, resulting in difference in solar cell performance. Compared with monolayer or stacked bilayer, multilayer graphene helps to achieve improved solar cell performance due to superior electrical conductivity. The all-layered-materials Schottky barrier solar cell employing WS2 as a photoactive semiconductor exhibits efficient photon absorption in visible spectral range, yielding 3.3 % photoelectric conversion efficiency with multilayer graphene contact. Carrier transport at graphene/WS2 interface and interfacial recombination process in the Schottky barrier solar cells are examined.
Due to their exceptional flexibility and transparency, CVD graphene films have been regarded as an ideal replacement of indium tin oxide for transparent electrodes, especially in applications where electronic devices may be subjected to large tensile strain. However, the search for a desirable combination of stretchability and electrochemical performance of such devices remains a huge challenge. Here, we demonstrate the implementation of a laminated ultrathin CVD graphene film as a stretchable and transparent electrode for supercapacitors. Transferred and buckled on PDMS substrates by a prestraininig-then-buckling strategy, the 4-layer graphene films maintained its outstanding quality, as evidenced by Raman spectra. Optical transmittance of up to 72.9% at a wavelength of 550 nm and stretchability of 40% were achieved. As the tensile strain increased up to 40%, the specific capacitance showed no degradation and even increased slightly. Furthermore, the supercapacitor demonstrated excellent frequency capability with small time constants under stretching.
As an emerging technology, forward osmosis (FO) has shown great promise in energy production from the mixing of fresh water and seawater in estuaries. However, the power density levels of the present commercial FO membranes hinder their practical applications in power generation due to the requirement for extremely large areas of membrane. Here, we use functionalized porous-single-layer graphene as a FO membrane and study the transport performances of the membrane using molecular dynamics simulation. For the FO system using fluorinated porous graphene (pore-diameter 11.7 Å, porosity 10%), with an excellent performance for salt rejection, the water flux is 28.1 L cm−2 h which is about 1.8 × 104 times higher than that of a typical cellulose triacetate membrane. Such high water flux will certainly bring about a very high power density in pressure retarded osmosis power generation. This work may generate potential opportunities for functionalized graphene in FO power generation, seawater desalination and so forth.
For developing high performance graphene-based nanocomposites, dispersal of graphene nanosheets in polymer hosts and precise interface control are challenging due to their strong interlayer cohesive energy and surface inertia. Here we report an efficient method to functionalize graphene nanosheets. The initiator molecules were covalently bonded to the graphene surface via a diazonium addition and the succeeding atom transfer radical polymerization linked polystyrene chains (82 wt% grafting efficiency) to the graphene nanosheets. The prominent confinement effect arising from nanosheets resulted in a 15 °C increase in the glass transition temperature of polystyrene compared to the pure polymer. The resulting polystyrene nanocomposites with 0.9 wt% graphene nanosheets revealed around 70% and 57% increases in tensile strength and Young's modulus. The protocol is believed to offer possibilities for optimizing the processing properties and interface structure of graphene-polymer nanocomposites.
Graphene, a monolayer of carbon atoms arranged in a honeycomb structure, is a unique material with outstanding properties that may be useful in applications ranging from electronic devices to energy storage devices. The versatile properties of graphene make it suitable for use in flexible and transparent optoelectronics, biological sensors, energy storage and conversion devices, electromechanical devices, and heat spreaders. This review focuses on recent progress in methods for graphene growth, modification, and transfer, and the uses of graphene as a transparent conducting electrode in flexible organic optoelectronic devices. Although prototypical laboratory-scale graphene-based devices have been prepared to demonstrate the advantages of graphene, many challenges must be addressed before such devices can be realized commercially.