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Flexible Asymmetric Micro-Supercapacitors Based on Bi2O3 and MnO2 Nanoflowers: Larger Areal Mass Promises Higher Energy Density
Abstract
A flexible asymmetric supercapacitor (ASC) with high energy density is designed and fabricated using flower-like Bi2O3 and MnO2 grown on carbon nanofiber (CNF) paper as the negative and positive electrodes, respectively. The lightweight (1.6 mg cm−2), porous, conductive, and flexible features make the CNF paper an ideal support for guest active materials, which permit a large areal mass of 9 mg cm−2 for Bi2O3 (≈85 wt% of the entire electrode). Thus, the optimal device with an operation voltage of 1.8 V can deliver a high energy density of 43.4 μWh cm−2 (11.3 W h kg−1, based on the total electrodes) and a maximum power density of 12.9 mW cm−2 (3370 W kg−1). This work provides an example of large areal mass and flexible electrode for ASCs with high areal capacitance and high energy density, holding great promise for future flexible electronic devices.
... X-ray photoelectron spectroscopy (XPS) studies also confirmed the existence of MnO 2 . As Fig. 2c displayed, the highresolution image of Mn 2 P XPS spectrum shows two peaks centered at 642.2 eV and 654.0 eV, which are corresponded to Mn 2p 3/2 and Mn 2p 1/2 with a spin energy separation of 11.8 eV, agreeing well with the previously reports for MnO 2 [24,[50][51][52]. As shown in Fig. S3, the two Mn 3 s peaks has a separation of binding energy (ΔE) of 5 eV, which is between 4.7 and 5.4 eV for Mn 4+ and Mn 3+ , respectively. ...
... The areal and specific capacitances for the whole electrode were 3240 mF/cm 2 and 178 F/g at 4 mA/cm 2 (Fig. 3c), respectively. The values are higher than those reported MnO 2 /CC [52][53][54] and MnO 2 /graphene [33]. The corresponding areal capacitance of pure MnO 2 nanograsses was calculated to be 2088 mF/cm 2 by excluding the contribution of carbon substrate (Fig. 3d and Fig. S7). ...
A R T I C L E I N F O Keywords: MnO 2 porous carbon cloth asymmetric supercapacitor high capacitance high energy density A B S T R A C T Flexible solid-state supercapacitors (SCs) have shown great potential in portable electronics. However, the development of MnO 2-based electrodes for flexible SCs is hampered by the low energy density, especially on the whole electrode basis, as a result of the small mass loading and poor utilization of MnO 2. Here high mass loading of 4.5 mg/cm 2 and large capacitance of 464 F/g (2088 mF/cm 2) for MnO 2 nanograsses were achieved by taking use of porous carbon cloth (TCC) which has large specific surface area. Benefiting from the full utilization of MnO 2 , high energy density of 841 μWh/cm 2 and robust cyclic stability (96% capacitance retention after 20000 cycles) are achieved by assembling an efficient asymmetric supercapacitor (ASC) with 2 V operating voltage. These results open up new paths for developing high-performance electrode materials and applying for advanced energy storage devices.
... Here, the enhanced (002) peak in LIGF-C4 indicates a more perfection of a graphitic structure after incorporating SWCNT. Conversely, the LIGF-C4/MnO 2 hybrid presents a weaker (002) diffraction peak in comparison with LIGF and LIGF-C4, which may be originated from the poor crystallinity of the resultant MnO 2 nanoparticles [40]. Furthermore, the characteristics peaks at around 37.7 and 65.6 in LIGF-C4/MnO 2 can be assigned to (211) and (002) planes of a-MnO 2 (JCPDS card No. 44e0141), respectively [40]. ...
... Conversely, the LIGF-C4/MnO 2 hybrid presents a weaker (002) diffraction peak in comparison with LIGF and LIGF-C4, which may be originated from the poor crystallinity of the resultant MnO 2 nanoparticles [40]. Furthermore, the characteristics peaks at around 37.7 and 65.6 in LIGF-C4/MnO 2 can be assigned to (211) and (002) planes of a-MnO 2 (JCPDS card No. 44e0141), respectively [40]. The Raman spectra of LIGF, SWCNT and LIGF-C4/MnO 2 are displayed in Fig. 3b, all of which possess three distinct peaks at~1350,~1590, and~2700 cm À1 , corresponding to the D, G, and 2D bands of graphitic carbon, respectively [41]. ...
Hybrid nanocomposites comprised of metal oxide nanoparticles and three-dimensional (3D) graphene possess the advantages of metal oxide and graphene, which have generated extensive attention. Here, we fabricate flexible micro-supercapacitors (MSCs) based on hybrid materials of single-walled carbon nanotubes (SWCNT)-bridged laser-induced graphene fibers (LIGF) decorated with manganese dioxide (MnO2) nanoparticles. SWCNT is deposited on the LIGF surface and the space between LIGF, which can bridge LIGF to form more conductive paths and provide more active areas to grow with MnO2 nanoparticles. Profiting from the synergistic effect between conductive SWCNT-bridged LIGF network and the MnO2 nanoparticles with high theoretical capacitance, the obtained flexible MSCs based on LIGF-C4/MnO2 hybrid electrodes deliver an outstanding areal capacitance of 156.94 mF cm⁻², which is about 8 times higher than that of LIGF-MnO2 based MSC (20 mF cm⁻²). Additionally, the LIGF-C4/MnO2 MSCs also exhibit considerable areal energy density of 21.8 μWh cm⁻², long-term cycling stability, remarkable modular integration capability, and exceptional mechanical flexibility (with 90.5% capacitance retention after 1200 bending cycles). Therefore, the design of hybrid electrode materials proposed in this work offers a facile and novel method to develop flexible energy storage devices with high performance, suggesting great prospects for applications in future various wearable electronics.
... The areal capacitance of the device can reach 427.9 mF cm − 2 (Fig. S25c) [75]. We calculated and compared the energy and power density values of the ASC with those reported in previous papers (Fig. 7c) [43,58,[76][77][78][79][80][81][82]. The as-prepared asymmetric device yields an energy density of 116.5 μWh cm − 2 at a power density of 700 μW cm − 2 . ...
Intercalation-pseudocapacitance materials are attracting increasing interest as promising electrodes for use in high-capacitance supercapacitors. However, these materials typically exhibit unsatisfactory rate performances due to their relatively slow cation-insertion process. Under high mass loading, their rate performances are even further degraded. Herein is presented our fabrication of an oxygen vacancy-rich h-WO3/ort-WO3·0.33H2O heterophase structure (HOHS) by a facile hydrothermal synthesis. The HOHS has a split-level nanotubes-on-nanoplates morphology and its formation and energy-storage mechanisms are discussed in detail. The HOHS exhibits a collaborative charge-storage mechanism involving surface redox and proton intercalation, and the capacitance contribution associated with the proton intercalation can be regulated over a wide range. By achieving a trade-off between the surface-limited pseudocapacitance and intercalation-limited behaviours and regulating its morphology, the HOHS electrode with an ultra-high mass loading of 10.8 mg cm⁻² delivers a high areal capacitance of 2552 mF cm⁻² at 1 mA cm⁻² and excellent long-term stability. More importantly, the rate performance of the HOHS (78% capacitance retention at 20 mA cm⁻² in comparison to 1 mA cm⁻²) is better than those reported for WO3-based materials. This strategy opens avenues for the fundamental study of the regulation of the energy storage mechanism and the achievement of a trade-off between the capacitance and rate capability in high-mass-loading electrodes.
... As the FSCs discussed before, twisted and stretchy FSCs are necessary for innovative electronics, for instance, self-powered polymer sensors, polymer LEDs as well as solar cells, and sharp matrix demonstrations [127]. Using early findings on twisted SCs, buckling SWNT or polydimethylsiloxane (PDMS) electrodes have garnered broad interest owing to their tendency to withstand strains of a maximum of 140% without negotiating resistance [128,129]. ...
The demand for highly efficient energy storage devices having high energy and power densities is increasing exponentially. In this regard, supercapacitors (SCs) have got great attention due to fast power generation and longer cyclic life. A range of electrodes has been explored for SCs applications including C-carbon, metal/carbon hybrids, metal oxides, etc. Among these, carbon-based electrodes have shown tremendous potential because of their hierarchical structure, electrical conductivity, and large surface areas. Still, carbon-based SCs offer limited energy density which strongly limits its application to a broader scale. A range of strategies was presented to boost the energy density of C-based SCs like developing highly porous nanos-tructures, introducing heteroatoms for pseudocapacitance, compositing with other forms of carbon, etc. Very recently, carbon-based electrodes have found great applications in wearable electronics owing to the fact that thin and flexible carbon electrodes chemistries can be readily obtained. This has opened new avenues in energy harvesting and utilization. In this chapter, we will provide insights into synthesis strategies of carbon-based wearable electrodes and their potential applications.
... As the FSCs discussed before, twisted and stretchy FSCs are necessary for innovative electronics, for instance, self-powered polymer sensors, polymer LEDs as well as solar cells, and sharp matrix demonstrations [127]. Using early findings on twisted SCs, buckling SWNT or polydimethylsiloxane (PDMS) electrodes have garnered broad interest owing to their tendency to withstand strains of a maximum of 140% without negotiating resistance [128,129]. ...
... Figure 4e exhibits the Ragone plot showing the energy densities as a function of power densities. The maximum areal energy density of 550 μW h cm −2 was achieved for ACC//ACC SSC, a value almost 6-fold as high as that for Bi 2 O 3 /CNF//MnO 2 /CNF, 61 4-fold higher than that of TCC//TCC SSC, 44 and also comparable to that reported for CC-based SSCs in Table S5. Additionally, the maximum volumetric energy density is calculated to be 6.1 mW h cm −3 , which is among the best values reported for other CC-based SSCs (Table S5). ...
... It illustrates that the MnO 2 /CNT-1 applied in device also have higher capacitance and performance than pure MnO 2 and pure CNT. As shown in Ragone plots (Fig. 4d), the AC//MnO 2 /CNT-1 can achieve the energy density of 32.00 Wh kg -1 at 413.70 W kg -1 , which are superior than those of other MnO 2 -based asymmetric supercapacitors in the literatures (Table S1) [39,[53][54][55][56][57].As shown in Fig. 4e, the stability of the AC//MnO 2 /CNT-1 device was conducted by cyclic charge/discharge for 6000 cycles at 5 A g -1 . The coulombic efficiency of around 100% and capacitance retention ratio of 78.26% were achieved after 6000 cycles. ...
Metal–oxygen batteries have been growing rapidly as an energy storage technology in light of their high specific energy density. However, waste metal–oxygen batteries will raise many environmental issues; therefore, the recycling and reusing of the spent metal–oxygen batteries has attracted great attention. Herein, we report the 2-phenyl-4,4,5,5-tetramethylimidazoline-1-oxyl-3-oxide (PTIO) as a redox mediator for manganese–oxygen battery (MOB). Trace amounts of PTIO result in the discharge capacity of MOB increase to 2588 mAh g⁻¹ and enhance the formation of manganese dioxide (MnO2) with toroidal appearance and high crystallinity on the cathode. After being used, the dismantled MnO2/carbon nanotube (CNT) cathode can be reused as an electrode for supercapacitor via simple calcining at mild temperature. The recycled free-standing MnO2/CNT electrode demonstrates an exceptional specific capacitance (253.86 F g⁻¹) at a current density of 0.5 A g⁻¹ in a 0.5 M Na2SO4 electrolyte. Moreover, we prepare an asymmetric supercapacitor fabricated with the recycled MnO2/CNT electrode and activated carbon (AC), which exhibits excellent energy density (32.00 Wh kg⁻¹ at 413.70 W kg⁻¹) with 78.26% retention over 6000 cycles. This work provides a promising strategy to derive high-quality and high-value MnO2/CNT electrode materials from the spent MOBs.
Graphical abstract
It’s the 2-phenyl-4,4,5,5-tetramethylimidazoline-1-oxyl-3-oxide (PTIO) as a redox mediator for manganese-oxygen battery (MOB). The recycled manganese dioxide (MnO2)/carbon nanotube (CNT) cathode can be reused as an electrode for supercapacitor via simple calcining at mild temperature. The recycled MnO2/CNT electrode shows the toroidal appearance and high crystallinity. Furthermore, the asymmetric supercapacitor fabricated with the MnO2/CNT free-standing electrode displays high specific capacitance, superior energy density, and good cyclic ability.
... Its highest capacity reaches 130.9 mA h g −1 at 0.2 A g −1 , and 61.6 mA h g −1 is still retained even at a high current density of 30 A g −1 (Fig. 4c). Specifically, its energy density of 104.7 W h kg −1 considerably overmatches the majority of recently reported quasi-solid-state SCs [26,28,29,[50][51][52] and LIBs [53] (Fig. 4d). To boost the operating voltage, two devices connected in series can offer a wide voltage of 3.4 V, and the capacity is doubled in parallel (Fig. 4e). ...
Although significant progress has been achieved in developing high energy aqueous zinc ion hybrid super-capacitors (ZHSCs), the sluggish diffusion of zinc ion (Zn 2+) and unsatisfactory cathodes still hinder their energy density and cycling life span. This work demonstrates the use of nitrogen doped mesoporous carbon nanospheres (NMCSs) with appropriately hierarchical pore distribution and enhanced zinc ion storage capability for efficient Zn 2+ storage. The as-prepared aqueous ZHSC delivers a significant specific capacity of 157.8 mA h g −1 , a maximum energy density of 126.2 W h kg −1 at 0.2 A g −1 , and an ultra-high power density of 39.9 kW kg −1 with a quick charge time of 5.5 s. Furthermore, the ZHSC demonstrates an ultra-long cycling life span of 50,000 cycles with an exciting capacity retention of 96.2%. More interestingly, a new type of planar ZHSC is fabricated with outstanding low-temperature electrochemical performance , landmark volumetric energy density of 31.6 mW h cm −3 , and excellent serial and parallel integration. Mechanism investigation verifies that the superior electro-chemical capability is due to the synergistic effect of cation and anion adsorption, as well as the reversible chemical ad-sorption of NMCSs. This work provides not only an innovative strategy to construct and develop novel high-performance ZHSCs, but also a deeper understanding of the electro-chemical characteristics of ZHSCs.
... High-resolution spectrum of manganese in Fig. 2c shows that two peaks appear at 642.4 eV and 654.2 eV, corresponding to Mn 2p 3/2 and Mn 2p 1/2 , respectively. It is found that the spin energy separation of these peaks is 11.8 eV [29][30][31]. In the 1s spectrum of oxygen shown in Fig. 2d, three characteristic peaks at 532. ...
Flexible and self-healing supercapacitors are urgently needed to meet the practical applications of flexible and wearable electronics. Herein, we have prepared a flexible and self-healing supercapacitor by sandwiching a self-healing physically cross-linked PVA–H2SO4 electrolyte separator between two activated carbon cloth (ACC)/MnO2 electrode films. The ACC/MnO2 electrode is prepared by activation of carbon cloth in air at medium temperature and then decorated by MnO2 nanoflakes through hydrothermal growth, which provides the flexibility and electrochemical performance. The self-healing of supercapacitor originates from the self-healing physically cross-linked PVA–H2SO4 electrolyte, which can enable the recombination of the broken interfaces and the self-healing of the supercapacitor through dynamic hydrogen bonding. As a result, the supercapacitor demonstrates excellent electrochemical performance (high areal specific capacitance of 886.7 mF cm−2 at 1 mA cm−2 and excellent cycling performance with a capacitance retention of 87.69% over 10,000 cycles), good self-healing capability with ~ 80% capacitance retention after 5 cutting/healing cycles), and outstanding flexibility.
... eV) and Mn 2p 3/2 (641.1 eV) peaks using the XPS best peak fitting with Gaussian modes were caused by the overlap of Mn 3+ and Mn 4+ ions [31]. Additionally, the separation value (>5.9 eV) between Mn 2p 3/2 and Mn 2p 1/2 was consistent with published reports [32]. The presence of carboxyl group and hydroxyl group was conductive for the pollutant adsorption according to the wide-range C 1s spectrum of MnO 2 NF/GO composites in Figure 3d. Figure 4a showed the effect of contact time for BbFA adsorption capacity on as-synthesized composites. ...
High-ring polycyclic aromatic hydrocarbons (PAHs, Benzo[b]fluorathene (BbFA), etc.) are difficult to biodegrade in the water environment. To address this issue, an innovative method for the preparation of MnO2 nanoflower/graphene oxide composite (MnO2 NF/GO) was proposed for adsorption removal of BbFA. The physicochemical properties of MnO2 NF/GO were characterized by SEM, TEM, XRD, and N2 adsorption/desorption and XPS techniques. Results show that the MnO2 NF/GO had well-developed specific surface area and functional groups. Batch adsorption experiment results showed that adsorption capacity for BbFA was 74.07 mg/g. The pseudo-second-order kinetic model and Freundlich isotherm model are fitted well to the adsorption data. These show electron-donor-acceptor interaction; especially π-π interaction and π complexation played vital roles in BbFA removal onto MnO2 NF/GO. The study highlights the promising potential adsorbent for removal of PAHs.
In the present work, a MnO2/MWCNT hybrid nanocomposite was synthesized by the one-step hydrothermal method. The structural, vibrational, morphological, and chemical composition of the samples were investigated by powder XRD, FT-IR, FE-SEM, and XPS analysis techniques. The MnO2/MWCNT hybrid electrode exhibited remarkable electrochemical performance with a high specific capacitance of 249 F/gat 0.5 A/g and the life cycling performance (95.5% retention after 2500 cycles at a current density of 10 A/g)in 1 M Na2SO4 electrolyte. Moreover, the constructed asymmetric-based supercapacitor (ASC) was used for PVA/1MNa2SO4 solid-state electrolyte. As-constructed ASC device achieved a high specific capacitance of 52 F/gat the current density 2 Ag⁻¹and the high power density and energy density of 8000 W kg⁻¹ and 19.50 W h kg⁻¹, respectively. The ASC has exhibited excellent cycle stability of 2000 cycles at the current density of 10 Ag⁻¹with capacitance retention of 94%.
Graphical abstract
Self-charging power systems, which can simultaneously achieve energy harvesting and storage, play a significant role in the field of energy technology. Nevertheless, the traditional integrated systems are not only severely restricted by the energy availability, but also have a complex architecture. Herein, a novel chemical self-charging aqueous zinc ion battery (CSCAZIB) with a two-electrode structure is reported. In such a self-powered system, the discharged cathode and oxygen in air will undergo spontaneous redox reactions and self-charging. A defect coupled nitrogen modulated zinc manganite vertical graphene array (N-ZnMn2O4-x/VG) is designed as the cathode for CSCAZIBs. Benefiting from the high surface area, rich active sites, fast electron/ion diffusion, and strong structural stability, the assembled device not only shows a large specific capacity (222 mA h g-1 at 0.1 A g-1) and good rate capability (61.58% retention from 0.1 to 3 A g-1) along with admirable cycle life (92.6% retention after 3000 cycles at 1.0 A g-1), but also delivers excellent energy density (278 W h kg-1) and remarkable power density (3.62 kW kg-1). The as-assembled CSCAZIBs could be self-charged to 1.5 V after oxidation in an ambient environment for 30 h, and present a decent specific capacity of up to 176.8 mA h g-1 at 0.2 A g-1. Significantly, even in chemical or/and galvanostatic charging hybrid modes, the CSCAZIBs can still work normally. This work expands a promising prospect for rechargeable aqueous metal ion batteries, and simultaneously realizes energy harvesting, conversion and storage.
Flexible supercapacitors represent an attractive technology for the next generation of wearable consumer electronics as power sources but usually suffer from relatively low energy density. It is highly desired to construct high‐performance electrodes for the practical applications of supercapacitors. Here, inspired by the natural structure of the spider web, an elaborate design of binder is reported through a biosynthesis process to construct flexible electrodes with both excellent mechanical properties and electrochemical performance. Through this strategy, a spider‐web‐inspired 3D structural binder enables large ion‐accessible surface area and high packing density of active electrode material as well as efficient ion transport pathways. As a result, a high areal capacitance of 4.62 F cm‐2 and a high areal energy density of 0.18 mW h cm‐2 is achieved in the composite electrodes and symmetric supercapacitors, respectively, demonstrating a promising potential to construct flexible energy storage devices for diverse practical applications. A spider‐web‐inspired composite electrode is developed by biosynthesis process. With the 3D structural binder, electrode material particles are tightly entangled in the bacterial cellulose 3D framework, endowing electrodes with excellent mechanical performance and facilitated ion diffusion. Thereby, spider‐web‐inspired composite electrodes exhibit high areal capacitance and demonstrate excellent rate capability, making them promising wearable and portable electronic applications.
Bismuth ferrite (BiFeO3) with high specific capacity and wide voltage window, fundamentally stores charge through the reversible redox reactions of cations, but usually suffers from poor rate capability and bad cycling stability, due to its densely-packed crystal structure and multi-electron redox reaction kinetics. We present a novel route to regulate nanoflake network architectures and oxygen vacancy defects of BiFeO3 through V doping and electrochemical induction without annealing. After consecutive charge/discharge process of BiFe0.95V0.05O3 fabricated by electrochemical deposition, the cycled BiFe0.95V0.05O3 (c-BiFe0.95V0.05O3) retains better structural stability and more oxygen vacancies than those of the annealed BiFe0.95V0.05O3, revealing the outstanding superiority of electrochemical induction. The c-BiFe0.95V0.05O3 electrode provides high rate capability and Li⁺ diffusion coefficient, mainly attributed to its nanoflake network architecture and abundant oxygen vacancies. The first-principle calculation demonstrates V doping and oxygen vacancies can enhance built-in electric field and construct fast ion transport channels for boosting rate capability. Based on the c-BiFe0.95V0.05O3 anode and the PPyHG (polypyrrole hydrogel) cathode, flexible asymmetric micro-supercapacitors can deliver an extremely wide voltage window of 2.3 V and a high areal energy density of 7.33 µWh cm⁻² at 63.7 µW cm⁻², reflecting its huge potential for flexible energy storage micro-devices.
Developing advanced negative and positive electrode materials for asymmetric supercapacitors (ASCs) as the electrochemical energy storage can enable the device to reach high energy/power densities resulting from the cooperative effect...
Transition metal oxides have shown renewed interest as promising electrode materials for high-performance electrochemical energy storage devices. However, their cycle stability deteriorates significantly with increasing mass loading due to the sluggish electrolyte ion diffusion kinetics and limited accessible surface area. Herein, commercial-level mass-loading MnO2 up to 9.14 mg cm-2 with rational ion diffusion channels was fabricated by a gassing-assisted electrodeposition route, in which MnO2 was deposited at an over-potential with an obvious oxygen evolution reaction. The robust channels in MnO2 not only facilitate the electrolyte ion diffusion process but also increase the accessible area for the insertion/extraction of electrolyte ions during electrochemical reactions. The resultant MnO2-based electrode exhibits the highest areal capacitance of 1.57 F cm-2 (in a Na+-based aqueous electrolyte), with a rate retention percentage of 76% when the current density increases by 20-fold. More impressively, the configured hybrid ion supercapacitor device with the fabricated MnO2 as a cathode delivers excellent cycle stability (in ion electrolytes Na+, Zn2+, and Mg2+), superior to most reported state-of-the-art energy storage devices. The proposed strategy here will provide a new opportunity for promoting the further development and practical application of aqueous energy storage devices by enhancing the true performance under a commercial-level mass-loading.
Recently reported ultraviolet (UV) detectors majorly focus on exploration of photodetection properties like photon absorption and electron‐hole pair generation to improve the photoresponsivity. However, UV sensors also have a potential advantage of monitoring the excessive UV exposure on skin. In this work, bismuth oxide/SnO2 quantum dots (QDs) vertical‐junction‐based self‐powered UV photodetector and optical UV filter are demonstrated. β‐Bi2O3 nanofibers are synthesized via electrospinning technique and SnO2 QDs are synthesized using a facile, single step hydrothermal process. Detailed morphological studies reveal the formation of 1D‐Bi2O3 and 0D‐SnO2. The fabricated self‐powered Bi2O2/SnO2‐based p–n heterojunction device exhibits a maximum responsivity of 62.5 µA W−1 and specific detectivity (D*) of 4.5 × 109 Jones attributing to the high absorption coefficient of β‐Bi2O2 nanofibers and SnO2 QDs in the UV region. Further, the 1D β‐Bi2O3 nanofibers and 0D SnO2 QDs are coated onto disposable cloth substrate to fabricate the UV optical filter which exhibits an exceptional ultraviolet protection factor of 159 and the photodetector device demonstrates high stability and reproducibility even after 1000 bending cycles. The strategy outlined here paves the way for development of bifunctional, cost‐effective design and construction of wearable UV sensors and protective devices for advanced nano‐electronic applications. Flexible self‐powered solar‐blind photodetector and ultraviolet (UV) filter based on β‐Bi2O3 nanofibers/SnO2 quantum dots Schottky heterojunction is demonstrated. The UV filter is fabricated by decorating Bi2O3 and SnO2 quantum dots on polypropylene cloth which exhibits an excellent ultraviolet protection factor of 159.
Textile supercapacitors are a key enabler of future, wireless, textile based smart wearables. With high power densities and long cycle lives, textile supercapacitors can be readily paired with energy harvesters to power the wearable technology. However, the energy density of these devices remains low (of the order of μWh) and work to increase this through improvements in the electrode design are requiring ever more complex materials and manufacturing processes. This work presents a novel and safe organic electrolyte that can increase the energy density of a simple symmetric activated carbon textile supercapacitor by ~ 8 times when compared to previous devices utilizing an identical substrate and set of electrodes. With a capacitance of 34.0 mF.cm-2 and an energy density of 18.9 μWh.cm-2, this device showed excellent performance. The device also underwent a rarely seen test for calendar ageing and was found to still exhibit 48% capacitance retention after two months of calendar ageing. This novel electrolyte enables the production of high energy density electric double layer textile supercapacitors without the need for pseudocapacitve or battery-like electrode materials.
Aqueous battery-supercapacitor hybrid devices (BSHs) are of great importance to enrich electrochemical energy storage systems with both high energy and power densities. However, further improvement of BSHs in aqueous electrolytes is greatly hampered by operating voltage and capacity limits. Different from the conventional intercalation/de-intercalation mechanism, Bi2O3 implements charge storage by a reversible phase conversion mechanism. Herein, taking Bi2O3 electrode with wide potential window (from −1.2 to 1 V vs. saturated calomel electrode) and high capacity as battery-type anode, we propose that the overall performance of aqueous BSHs can be greatly upgraded under neutral condition. By paring with stable layer-structured δ-MnO2 cathode, a sodium-ion Bi2O3//MnO2 BSH with an ultrahigh voltage of 2.4 V in neutral sodium sulfate electrolyte is developed for the first time. This hybrid device exhibits high capacity (∼ 215 C g⁻¹ at 1 mA cm⁻²), relatively long lifespan (∼ 77.2% capacity retention after 1500 cycles), remarkable energy density (71.7 Wh kg⁻¹@400.5 W kg⁻¹) and power density (3204.3 W kg⁻¹@18.8 Wh kg⁻¹). Electrochemical measurements combining a set of spectroscopic techniques reveal the reversible phase conversion between bismuth oxide and metallic bismuth (Bi2O3 ⇋ Bi⁰) through Bi²⁺ transition phase in neutral sodium sulfate solution, which can deliver multielectron transfer up to 6, leading to the high-energy BSHs. Our work sheds light on the feasibility of using Bi2O3 electrode under neutral condition to address the issue of narrow voltage and low capacity for aqueous BSHs.
Endowing natural biological objects, such as plants or their parts, with non‐native and targeted electroactivity is an appealing challenge in nano‐biotechnology, which if addressed will circumvent the biomass carbonization and promote the emission‐free transformation of raw bioresources for green energy. Here, a general concept to produce supercapacitor electrodes from plant stems is reported, which exhibit promising electroactivity and cytocompatibility. The core innovation is to apply a conformal electroactive coating onto the surfaces of hyperbranched channels of plant stem by interfacial self‐assembly. The electroactive plant stem can be employed as a functional supercapacitor electrode, the capacitance of which is up to 2.35 F. Furthermore, more than 98% cell viability is well maintained after the plant stem electrode is incubated with MCF‐7 cells for 72 h, and even after 100 discharge–recharge cycles, suggesting this plant stem electrode has excellent cytocompatibility and cycling stability. This energy storing plant stem gives rise to new opportunities for integrating natural bioresources with artificial electroactive nanomaterials for cytocompatible energy storage devices. A novel energy storing plant stem and its usability as a supercapacitor electrode is reported. The plant stem directs the interfacial assembly of a conformal polyaniline coating that renders electroactivity to the plant stem, which can be employed as a functional supercapacitor electrode. Furthermore, this plant electrode demonstrates excellent cytocompatibility and cycling stability.
The in-situ electrodeposited bismuth catalyst for vanadium redox flow batteries is typically prepared by dissolving Bi³⁺ ions in the electrolyte and spontaneously electrodepositing metallic bismuth onto the carbon fiber surface at the beginning of charge process after battery assemble, which therefore has intriguing superiorities including facile preparation, catalyst on-line restoration and long service life. Whether achieving uniform catalyst distribution inside the porous electrode directly influences battery performance. In this work, the effects of the catalyst loading, initial Bi³⁺ concentration and electrodeposition current density on the catalyst distribution, catalyst morphology and battery performance are comprehensively investigated. It is found that the ratio between the optimal electrodeposition current and theoretical limiting current keeps around 50% for different initial Bi³⁺ concentrations. The optimal case of constant-current electrodeposition is the initial Bi³⁺ concentration of 2 mM and electrodeposition current density of 10 mA cm⁻². More importantly, the intermittent catalyst electrodeposition method is proposed to address the conflict between electrodeposition current density and catalyst distribution, which delivers superior catalyst distribution and battery performance compared to the optimized constant-current electrodeposition. The battery with intermittent catalyst electrodeposition achieves a high voltage efficiency of 85.4% at 320 mA cm⁻².
Efficient improvement of the energy density and overall electrochemical performance of fiber‐shaped asymmetric supercapacitors (FASCs) for practical applications in portable and wearable electronics requires highly electrochemically active materials and a rational design. Herein, two‐step phosphorization (TSP) processes are performed to directly grow 3D well‐aligned NiCoP@NiCoP (NCP@NCP TSP) nanoflake arrays (NFAs) on carbon nanotube fibers (CNTFs). Profiting from the metallic characteristics and excellent electrochemical performance of NiCoP and the hierarchical design of the core–shell heterostructure, the NCP@NCP TSP NFAs/CNTF hybrid electrode exhibits significantly improved electrochemical performance. The as‐fabricated NCP@NCP TSP NFAs/CNTF electrode possesses an ultrahigh areal capacitance of 10 035 mF cm−2 at a current density of 1 mA cm−2, with excellent rate capability and cycling stability. Furthermore, an FASC device with a maximum operating voltage of 1.6 V is assembled by adopting NCP@NCP TSP NFAs/CNTF as a positive electrode, hierarchical TiN@VN core–shell heterostructure nanowire arrays (NWAs)/CNTF as negative electrode, and KOH‐PVA as a gel electrolyte. The FASC device exhibits a high areal capacitance of 430.4 mF cm−2 and an ultrahigh energy density of 51.02 mWh cm−3. Thus, the rationally designed NiCoP@NiCoP electrode is a promising candidate for incorporation into next‐generation wearable and portable energy‐storage devices. Hierarchical NiCoP@NiCoP nanoflake arrays core–shell heterostructures directly grown on carbon nanotube fibers (CNTFs) as novel binder‐free positive electrode are skillfully constructed. Fiber‐shaped asymmetric supercapacitors are successfully fabricated by the as‐prepared NiCoP@NiCoP nanoflake arrays/CNTF and TiN@VN nanowire arrays/CNTF exhibits an ultrahigh energy density of 51.02 mWh cm−3 and thus demonstrates great potential for next‐generation wearable energy storage devices.
Porous micro/nano structured materials have gained much interest since they have many excellent properties wisely as large surface area and confined pore structure for various applications in electrochemistry such as, catalysis, sensing and energy storage devices. Among various characteristics, structure of porous metal oxides plays vital role in determining electrochemical performance. Fortunately, nano-structuration and porosity conjunction for transition metal oxides ascertains a role in enhancing electrochemical storage of electrodes for charge storage devices mainly due to: (i) large surface area for charge storage; (ii) easy access over active material for electrolyte ions and (iii) fast electrolytic ion transportation through porous channels. This chapter reviews the current development of nanoporous transition metal oxide-based materials, with specific focus on advanced electrochemical supercapacitor applicatin.
Electrochemical energy storage is a key technology for a clean and sustainable energy supply. In this respect, supercapacitors (SC) have recently received considerable attention due to their excellent performance, including high‐power density and long‐cycle life. However, the poor binding strength between the active materials and substrate, the low active material loading, and small specific capacitance hinder the overall performance improvement of the device. In this study, an ultrahigh‐areal capacitance flexible SC based on the Al micro grid‐based hierarchical vertically aligned carbon nanotubes (VACNTs) is studied. Interestingly, the Al micro grid‐based VACNTs exhibit ultrahigh loading (13 mg cm−2), and the as‐fabricated VACNTs electrode display outstanding electrochemical performance, including an impressive areal capacitance of 1,300 mF cm−2 at the current density of 13 mA cm−2 and excellent stability with a retention ratio of 90% after 20,000 cycles at the current density of 130 mA cm−2. Furthermore, the hierarchical VACNT electrodes show excellent mechanical flexibility when assembled into quasi‐solid‐state SC using Na2SO4‐PVA gel as the electrolyte. The capacitance of this device is hardly changed bending different angles, even 180°. This study demonstrates the tremendous potential of Al micro grid‐based hierarchical VACNTs as electrodes for high‐performance flexible and wearable energy storage devices. A hierarchically aligned carbon nanotube material is developed as a flexible electrode to fabricate ultrahigh‐areal capacitance supercapacitors. Benefiting from the laser‐etched hierarchical micro grid configuration, the electrode provides outstanding electrochemical performance and robust flexibility. This approach provides an innovative path for the next‐generation flexible electronic device.
Aqueous bismuth based anode have received intensive interest in recent years. However, further advances in rate capability and cycling stability remain challenging. Herein, a porous conductive network is first...
Asymmetric supercapacitors (ASCs) can substantially broaden their working voltage range, benefiting from the advantages of both cathode and anode while breaking through the energy storage limitations of corresponding symmetric cells. Wide voltage aqueous ASCs hold great promise for future electronic systems that require satisfied energy density, power density, and cycle life, due to the advantages of aqueous electrolyte in terms of low cost, operational safety, facile manufacture, environment-friendly, and high ionic conductivity. This review will first briefly present an overview of the historical developments, charge storage mechanisms, and matching principles of wide voltage aqueous ASCs. Then, the cathode and anode materials with wide potential windows for building wide voltage aqueous ASCs over the last few decades are summarized. The next section details the optimization methods of aqueous electrolyte related to wide voltage aqueous ASCs. In addition, the basic device configurations of wide voltage aqueous ASCs are classified and discussed. Furthermore, several strategies are proposed for achieving high-performance wide voltage aqueous ASCs in terms of voltage window, specific capacitance, rate performance, and electrochemical stability. Finally, to motivate further research and development, several key scientific challenges and the perspectives are discussed.
A new double‐layer hybrid electrode based on MnO2 nanofibers was prepared by the electrostatic flocking method. Compared with the traditional dopping method, the MnO2 nanofibers can be embedded on surface of graphene/polyvinylidene fluoride (PVDF) composite coating. The symmetrical supercapacitor based on electrostatic flocking electrode was further assembled, which showed a high energy density of 12.1 Wh kg−1 and ultra‐long cyclic life of 109.4% after 10 000 cycles. The result was attributed to that electrostatic flocking MnO2 nanofibers were directly exposed to electrolyte, reducing interfacial resistance. The work provides a new way to prepare high‐performance electrode for various applications. A new double‐layer hybrid electrode based on MnO2 nanofibers was developed. The electrode was prepared by electrostatic flocking method. The electrode exhibited excellent electrochemical stability.
A solvothermal technique was used to synthesize nine different ferric oxide (Fe2O3) morphologies: rhomb (R), flower (F), hollow sphere (HS), crystal (C), elongated hexagon (EH), hexagon (H), sugar apple (SA), sand/spherical particle (SSP) and mixed particle (MP). X-ray diffraction, high-resolution transmission electron microscopy and selected area electron diffraction reveal six of the nine powders to be composed of the pure α-Fe2O3 structure, whereas the EH-Fe2O3, H-Fe2O3 and SA-Fe2O3 powders contain the mixed α-Fe2O3/Fe3O4 structure. The F-Fe2O3 powder has the highest total specific pore volume (0.059 cm³ g⁻¹), the largest average pore size (23.983 nm), and a high specific surface area (9.82 m² g⁻¹), which subsequently produce the highest specific capacitance of 218.49 F g⁻¹. X-ray photoemission spectroscopy and energy dispersive spectroscopy detect H2O molecules and K⁺ adsorption on the F-Fe2O3 electrode and the reduction of Fe³⁺ to Fe²⁺ in the charged state, whereas H2O molecules and K⁺ ions are released from the F-Fe2O3 electrode, and Fe²⁺ is oxidized to Fe³⁺ in the discharged state. The simulated K-inserted-α-Fe2O3 structure shows an increased electron density surrounding Fe atoms, which is indicative of Fe³⁺ reduction during the charged state. The F-Fe2O3 film is able to retain 76.81% of its 20th cycle value after 1,000 cycles. Four series-supercapacitor coin cells constructed from the F-Fe2O3 anode and the MnO2 cathode deliver an outstanding energy density of 10.96 Wh kg⁻¹ and power density of 0.461 kW kg⁻¹.
The re-stacking of graphene sheets leads to the far lower areal capacitance and energy density of the graphene-based micro-supercapacitors (MSC) than the expected. Herein, to solve this issue, a novel 0D/2D porous carbon integrated architecture (PC-IA) is ingeniously in-situ constructed by a two-step fabrication strategy, which is realized by the synthesis of 0D/2D TiC integrated architecture in a molten salt-containing Ti environment based on graphene nanosheets (GNS) as the template followed by high-temperature chlorination. Interestingly, the newly synthesized PC-IA shows huge advantages compared with the original GNS, such as higher specific surface area, more abundant porosity, better wettability to electrolyte and more effective ion channels in the c-axis direction, etc. As a result, when PC-IA is used as the electrode material, the fabricated MSC exhibits excellent electrochemical performances, such as ultrahigh areal capacitance of 70.12 mF cm⁻² and high energy density of 9.48 μWh cm⁻². Moreover, the fabricated MSC also behaves excellent mechanical flexibility and can be easily adjusted in the voltage and capacitance by connecting multiple MSC devices in series and parallel. Hence, this work opens up a new way for the reasonable design of carbon-based electrodes, which has broad application prospects in various flexible/wearable electronic devices.
Metallic 1T phase MoS 2 (1T-MoS 2 ) nanosheets with large interlayer spacing are considered as high-energy electrode materials for supercapacitor, however, electrochemical storage mechanism of 1T-MoS 2 involves ion intercalation resulting in energy...
Present study investigates nano-Ni1-xCoxO (0.0 ≤ x ≤ 1.0) system by a scalable salt-templated synthesis and its potential for energy storage application. The system was characterized by XRD, Raman spectroscopy, XPS, TEM and electrochemical studies. An interesting phase relation was observed wherein NiO with rock salt structure yielded biphasic mixture (rock salt + spinel-type) followed by single-phasic spinel phase upon successive Co-substitution. A wider solubility of NiO in Co3O4 and appearance of biphasicity in NiO-rich region suggests that Co prefers +3 oxidation state, leading to relatively narrower rock-salt phase field. The crystallite size of 18–25 nm was estimated and TEM shows more uniform particles with narrower size distribution with decrease of metal-to-salt ratio during synthesis. Subtle transition from normal to inverse spinel upon Ni-substitution in Co3O4 could be deciphered by careful Raman spectroscopic analysis. The best electrochemical performance was observed for Ni0.5Co0.5O with maximum specific capacitance of 146 F g⁻¹ at 1 A g⁻¹ and 97% capacitance retention(1000 cycles). An asymmetric device fabricated with Ni0.5Co0.5O showed specific energy of 15.38Wh/Kg. Highlight of study is enhanced electrochemical performance of Ni0.5Co0.5O, over either of end members, due to richer redox chemistry owing to simultaneous presence of Ni and Co ions.
Supercapacitors (SCs) are being considered the next-generation energy storage devices due to their outstanding energy density and exceptional cyclic stability. A solid-state symmetric supercapacitor (ASC) has been designed using ternary MnO2/CuO/rGO hybrid as the anode and lemon peel (LP) derived activated carbon (AC) as the cathode. The MnO2/CuO/r-GO hybrid was synthesized via a simple hydrothermal method. A ternary MnO2/CuO/r-GO hybrid showed the specific capacitance of 793.14 F g⁻¹ at 1 A g⁻¹ with the life cycling performance of 94% retention after 10,000 cycles at a high current density of 10 A g⁻¹, owing to the synergistic effect of high conductive r-GO and high pseudocapacitive MnO2/CuO hybrid with high surface area (113.501 m² g⁻¹). The overall electrochemical performance of MnO2/CuO/r-GO hybrid electrode materials was improved when compared with pure MnO2 and MnO2/CuO electrode materials due to the combined effect of high specific capacitance MnO2 and CuO and high surface area and electrical conductivity of rGO. Moreover, the AC was derived from LP and studied its physics-chemical properties. The AC material exhibits a high specific capacitance of 206 F g⁻¹at 1 A g⁻¹ with outstanding capacitance retention of 96% even after 10,000 cycles. The assembled MnO2/CuO/r-GO//AC asymmetric supercapacitor (ASC) delivered a specific capacitance of 177 F g⁻¹ at 2 A g⁻¹ with a high energy density of 79.60 W h kg⁻¹ at a power density of 2430 W kg⁻¹ with the wide range of operating potential window (0–1.8 V). The ASC has exhibited excellent cycle stability with capacitance less than 10% after 10,000 cycles at 10 A g⁻¹.
The conductivity and structural intrinsic stability of cathode materials are the barriers to achieve high-performance fiber-shaped Zn-ion batteries (FZIBs). Here, amorphous H0.82MoO3.26 coated on carbon nanotubes fiber (noted as CHMO) is exploited as cathode materials for aqueous FZIBs with high energy density, excellent cycle stability and good omnidirectional flexibility. The amorphous H0.82MoO3.26 improves electron transfer and accelerates electrochemical reaction kinetic, as well as effectively suppresses structural degradation during repeated charge/discharge process. Meanwhile, the electrochemical behaviors combined with a series of in-situ/ex-situ characterizations verify that Zn²⁺ and H⁺ ions insert/extract into/from the CHMO fiber reversibly at the same time. The assembled battery delivers high energy density of 32.1 mWh cm⁻³ (based on the volume of cathode) and excellent capacity retention of about 67% after 5000 cycles at 700 mA cm⁻³, as well as splendid flexibility (about 91% capacity retention after bending 3500 times). Wearable NO2 gas sensor and pressure sensor integrated with fiber-shaped Zn//CHMO battery are also fabricated, which can operate stably with stable signal output.
The development of zinc ion batteries (ZIBs) with large capacity, high rate, and durable cathode material is a crucial and urgent task. NiCo2O4 (NCO) has received ever-growing interest as a potential cathode material for ZIBs, owing to the high theoretical capacity, rich source, cost-effective, and versatile redox nature. However, due to the slow dynamics of the NCO electrodes, its practical application in high-performance systems is severely limited. Herein, we report an electron density modulated NCO nanosheets (N-NCO NSs) with high-kinetics Zn²⁺-storage capability as an additive-free cathode for flexible all-solid-state (ASS) ZIBs. By virtue of the enhanced electronic conductivity, improved reaction kinetics, and increased active sites, the optimized N-NCO NSs electrode delivers a high capacity of 357.7 mAh g⁻¹ at 1.0 A g⁻¹ and a superior rate capacity of 201.4 mAh g⁻¹ at 20 A g⁻¹. More importantly, a flexible ASS ZIBs device is manufactured using a solid polymer electrolyte of a poly (vinylidene fluoride hexafluoropropylene) (PVDF-HFP) film. The flexible ASS ZIBs device shows superb durability with 80.2% capacity retention after 20000 cycles and works well in the range of −20–70 °C. Furthermore, the flexible ASS ZIBs achieves an impressive energy density as high as 578.1 W h kg⁻¹ with a peak power density of 33.6 kW kg⁻¹, substantially outperforming those latest ZIBs. This work could provide valuable insights for constructing high-kinetics and high-capability cathodes with long-term stability for flexible ASS ZIBs.
A lot of works have revealed that the introduction of Carbon nanotubes (CNTs) into oxide-based electrode materials is an efficient strategy to improve their energy storage performance. In this work, we firstly demonstrated the intrinsic effects of introduced CNTs for bismuth oxide (Bi2O3) electrode materials, including the physical, chemical and energy storage performance. Our results revealed that the optimal value of introduced CNTs into Bi2O3 is 1.5 % (in weight ratio), which demonstrated a specific capacitance of 1012 C g⁻¹ at 1 A g⁻¹, about 1.52 times higher than the pristine Bi2O3. The obtained optimal energy storage performance by introduced CNTs can be explained by; 1) the introduced CNTs were helpful to reduce the average particle size of Bi2O3 powder, here the particle size was greatly reduced from 363 nm to 112 nm; 2) the small Bi2O3 particle with the introduced CNTs demonstrated more than 1.97 times enhancement of specific surface area; 3) the total conductivity of the obtained composite electrode was greatly enhanced by 320.31 times and, 4) however, due to the lower theoretical capacity of CNTs, the total specific capacitance of composite electrode showed a significant reduction by introducing excess CNTs. We believe that this work provides a strong support to guide the introduction of CNTs into Bi2O3-based energy storage materials for optimizing electrochemical performance.
The flexible artificial intelligence and rechargeable electronic devices have been the research hotpot due to the status quo of energy crisis. However, the existing energy storage devices suffering from undesirable electrochemical performance, poor flexibility and toxicity, have unsatisfactory practical application prospect. Owing to unique stability, carbon‐based material has been the normal electrode of energy storage equipment. Recently, zinc hybrid supercapacitors attracted much attention. Herein, a high‐performance zinc‐ion hybrid micro‐supercapacitor is successfully constructed using hierarchical honeymoon‐like porous carbon frameworks as cathode by direct ink printing method. Due to the bivalent feature of zinc and electric double layered capacitive characteristic to porous carbon, the optimized device possesses excellent electrochemical performance of excellent specific capacity of 189.06 mAh g −1 at the current density of 1 mA cm −2 , high energy density of 76.38 Wh kg −1 , a power density of 499.94 W kg −1 and superior capacity retention of 95.71% at 10 mA cm −2 after 1000 cycle numbers. Through direct ink printing, the as‐assembled zinc hybrid micro‐supercapacitors based on flexible substrate exhibit outstanding flexibility with controllable active material mass loading.
Evolving cost‐effective transition metal phosphides (TMPs) using general approaches for energy storage is pivotal but challenging. Besides, the absence of noble metals and high electrocatalytic activity of TMPs allow their applicability as catalysts in oxygen evolution reaction (OER). Herein, CoNiP‒CoP2 (CNP‒CP) composite is in situ deposited on carbon fabric by a one‐step hydrothermal technique. The CNP‒CP reveals hybrid nanoarchitecture (3D‐on‐1D HNA), i.e., cashew fruit‐like nanostructures and nanocones. The CNP‒CP HNA electrode delivers higher areal capacity (82.8 μAh cm–2) than the other electrodes. Furthermore, a hybrid cell assembled with CNP‒CP HNA shows maximum energy and power densities of 31 μWh cm–2 and 10.9 mW cm–2, respectively. Exclusively, the hybrid cell demonstrates remarkable durability over 30 000 cycles. In situ/operando X‐ray absorption near‐edge structure analysis confirms the reversible changes in valency of Co and Ni elements in CNP‒CP material during real‐time electrochemical reactions. Besides, a quasi‐solid‐state device unveils its practicability by powering electronic components. Meanwhile, the CNP‒CP HNA verifies its higher OER activity than the other catalysts by revealing lower overpotential (230 mV). Also, it exhibits relatively small Tafel slope (38 mV dec–1) and stable OER activity over 24 h. This preparation strategy may initiate the design of advanced TMP‐based materials for multifunctional applications.
Due to its excellent electrochemical properties, MoO3 is considered to be a promising electrode material in the field of energy storage, but it still suffers low electronic conductivity and serious aggregation. Herein, the partially expanded graphite paper (EGP) with a three-dimensional porous structure is synthesized by a cathodic electrochemical exfoliation, serving as a conductive substrate for the in-situ growth of MoO3 nanobelts via a simple hydrothermal method. The self-supporting MoO3/EGP composite material directly used as the electrode material of the supercapacitor, shows a high specific capacitance of 7.1 F cm⁻² at 1 mA cm⁻². In addition, the assembled symmetrical supercapacitor by using MoO3/EGP as electrodes offers an energy density of 0.77 mWh cm⁻² at a power density of 2.41 mW cm⁻² and the capacitance retention is 84.1% after 5000 cycles at 10 mA cm⁻², indicating the excellent cyclic stability. The remarkable electrochemical performance of MoO3/EGP is attributed to the self-supporting porous structure of EGP with high electronic conductivity, which not only effectively prevents the aggregation of MoO3 nanobelts but also promotes the transfer kinetics of ion and electron.
The surfaces of nanoporous metals are easy to be oxidized under normal ambient condition. This usual attribute permits the exploration of metal-core oxide-shell structure that would be used for supercapacitors (SCs). However, the large-scale application of such electrodes is still limited by the intrinsically low ion diffusion coefficient, poor electronic conductivity and frustrating structural stability. Here we design a defect decorated hierarchical nanoporous CuMn2O4/Cu0.2Ni0.8O/CuxOy@ alloy electrode (HNP-TMO) by dealloying-coarsening-dealloying a sandwich-like NiCuMn/Ni/NiCuMn alloy and followed by self-combusting (2.1 mm s⁻¹). The sandwiched Ni can synergy with unoxidized alloy to provide excellent mechanical stability and electronic conductivity, while the hierarchically porous structure with robust defects can ensure rapid electron/ion transportation. Benefiting from these merits, the HNP-TMO electrode with high mass loading of 7.8 mg cm⁻² delivers an ultrahigh area capacity of 6.78 mAh cm⁻² at 10 mA cm⁻², good rate capability (maintaining 3.33 mAh cm⁻² at ultra-high current density of 100 mA cm⁻²) and outstanding cycling performance with capacity retention of 92.7% after 12000 cycles. Full symmetric supercapacitor also demonstrates high energy and power density of 0.17 mWh cm⁻² and 40.15 mW cm⁻², respectively, indicating the promise for practical energy storage applications.
Two-dimensional (2D) MXene materials have significant potential applications in electrochemical energy storage. A Ti3C2Tx MXene film can be used as a high-performance electrode for a flexible supercapacitor owing to its flexibility and excellent rate capability. However, Ti3C2Tx is usually only used as a negative electrode material because it can be easily oxidized under positive (anodic) potential. Herein, we report a simple filtration method to fabricate a hybrid cathode by mixing a colloidal solution of 2D Ti3C2Tx nanosheets and 1D MnO2 nanobelts to form an alternating MnO2/Ti3C2Tx stacked structure. Compared with pure Ti3C2Tx, the hybrid cathode has higher electrochemical stability toward anodic oxidation. The MnO2/Ti3C2Tx hybrid cathode delivers a high gravimetric capacitance of 315 F g⁻¹ at 10 mV s⁻¹ and a good rate capability of 166 F g⁻¹ at 100 mV s⁻¹. The high stability of the MnO2/Ti3C2Tx hybrid cathode is mainly attributed to the charge transfer-induced work function enlargement at the Ti3C2Tx and MnO2 heterointerface. Furthermore, a flexible asymmetric supercapacitor assembled using MnO2/Ti3C2Tx as the cathode and alkalized Ti3C2Tx as the anode delivers a high-voltage window up to 1.9 V. This work provides new insights for designing high-performance MXene-based cathode materials and devices for wearable electronics.
Bi2O3 is an outstanding electrode material due to its high theoretical specific capacity. Hence, the synthesis of δ-Bi2O3 materials with high oxygen-vacancy contents could improve their electrochemical performances but causes easy conversion to α-Bi2O3 with low oxygen-vacancy contents, leading to poor cycling stability and limited practical applications. To overcome these problems, an effective strategy for constructing high oxygen vacancies α-Bi2O3 on activated carbon fiber paper (ACFP) is developed in this study. To this end, ACFP/Bi(OH)3 is first synthesized by the solvothermal method and then converted to ACFP/α-Bi2O3 by in situ electrochemical activation. The proposed innovative electrochemical method quickly and easily introduces oxygen vacancies while preserving the three-dimensional structure, thereby promoting the charge transfer and ions diffusion in ACFP/α-Bi2O3. Consequently, the specific capacity of ACFP/α-Bi2O3 reaches 906 C g⁻¹ at 1 A g⁻¹, and the capacity retention remains above 70% after 3000 cycles, a value higher than that of δ-Bi2O3 (45%). Furthermore, the hybrid supercapacitor device assembled by ACFP/α-Bi2O3 delivers a maximum energy density of 114.9 Wh kg⁻¹ at 900 W kg⁻¹ and outstanding cycle stability with 73.56 % retention after 5500 cycles. In sum, the proposed ACFP/α-Bi2O3 with high performance and good stability looks promising for use as bismuth-based anode materials in supercapacitors and aqueous batteries.
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As a promising anode material, Bi2O3 has triggered great attention due to the combined advantages of high theoretical capacity, wide potential window and highly reversible redox process. However, the limited active sites and poor conductivity make the actual capacitance of Bi2O3 far from satisfaction, which greatly hinder its practical application in aqueous alkaline battery. Herein, a novel Bi-MOF derived hierarchical structured Bi2O3 is synthesized via controlling the calcination conditions. The N2 adsorption-desorption analysis indicates the large specific surface area (9.68 m² g⁻¹) and porous structure of hierarchical Bi2O3. The electrochemical experiments reveal that the hierarchical Bi2O3 delivers a high specific capacity of 219.4 mAh g⁻¹ at 1 A g⁻¹ and long-term stability of 83% after 2000 cycles. Such remarkable electrochemical performance generates from the full utilization of exposed active sites, fast diffusion of electrolytes and steady hierarchical structure. Apart from this, the assembled Ni/Bi aqueous alkaline battery also exhibits outstanding electrochemical performance and a high energy density of 36.8 Wh kg⁻¹ is achieved at 400.1 W kg⁻¹. This work may pave the way for exploring Bi-based high-performance anode materials for alkaline battery.
Binary metal oxides are deposited via simple chemical routes for high-performance energy storage applications. In this work, we developed nanostructures of BiMnO3 on Ni foam using a hydrothermal method. Initially, the (0 1 0) and (1 1 0) planes confirmed the presence of the BiMnO3 phase. Snow fungus-like nanostructure was transferred to porous interconnected nanoflakes with an increase in deposition time. These nanoflakes serve as large active sites that are beneficial for the diffusion of electrolytic ions that enhance the charge storage and transport process. Consequently, the two-dimensional interconnected nanoflakes showed a high diffusion coefficient, standard rate constant, and minimum transfer coefficient. In addition, BiMnO3 exhibited an aerial capacitance of 6000 mF cm⁻² (1500 Fg⁻¹) with an energy density of 102 Wh kg⁻¹ at an applied current density of 20 mA cm⁻². For practical applications, an asymmetric coin cell (ACC) device was assembled using BiMnO3 as the positive electrode and activated carbon as the negative electrode in 3 M aqueous KOH as an electrolyte. The fabricated ACC device had an energy density of 14.4 Wh kg⁻¹ at a power density of 50 W kg⁻¹ with a 1.2 V potential; the capacitive retention was 90 %, with 97 % Coulombic efficiency up to 5000 cycles. Accordingly, the results determined that BiMnO3 can be used as an electrode material for high-performance energy storage applications.
High-energy electrodes at high mass loadings (usually >8.0 mg cm-2 ) are desired for aqueous pseudocapacitors. Yet, how to overcome the thickness-dependent resistance increase of ion/electron transport in pseudocapacitive materials is still challenging. Herein, a high-performance electrode (denoted as AMC) adapted to high mass loading is achieved by promoting the Li-ion affinity of 3D MoO2 /carbon fabric. The experimental results and corresponding computational results reveal that the oxygen-activated surface of AMC, combined with the wettability and conductivity superiority of 3D graphite network, significantly facilitates the Li-ion adsorption and diffusion at the electrode/electrolyte interface, even at large thicknesses. Consequently, even at a high mass loading up to 8.1 mg cm-2 , the AMC electrode also displays an impressive specific capacity (567.5 C g-1 at 2.5 A g-1 ), substantially superior to most advanced pseudocapacitive electrodes. The strategy of boosting energy characteristic by enhancing the affinity of charge carriers is applicable to other pseudocapacitive electrodes.
Binder-free MnO2-based cathodes are critical to the development of aqueous Zn/MnO2 batteries. Here, conjugated microporous polymer aerogels (CMPAs) with columnar, rod and linear shapes are successfully prepared through Sonogashira-Hagihara cross-coupling reaction. Using them as precursors, we obtain the integrated high-conductivity carbon-based aerogels (C-CMPAs) by pyrolysis. Secondly, MnO2 nanosheet arrays are uniformly grown on the surface of C-CMPAs nanotubes([email protected]2) form a thin-walled cell configuration through a simple low temperature hydrothermal method. In this system, C-CMPAs serve as both current supporter and collector, while the cross-linked MnO2 flakes act as the active layer. This unique anisotropic structure not only greatly enlarges the contact area of electrode/electrolyte interfaces and supplies abundant electrochemically active sites, but shortens the Zn²⁺ ion insertion/extraction paths. Meanwhile, the high mechanical strength of core/shell structure between C-CMPAs and MnO2 renders long-term cycling life. Finally, binder-free [email protected]2-based aqueous zinc-ion batteries provide an unprecedented capacity of 670.7 mAh g⁻¹ at 0.1 A g⁻¹, good rate performance and excellent cycle stability (94.1% after 600 cycles). More importantly, the Zn//[email protected]2 aqueous battery provides high energy density of 536.6 Wh kg⁻¹ at 80.3 W kg⁻¹, superior to most similar reports, indicating the great potential of high-performance rechargeable batteries.
Crystallized transition metal oxides were widely used as the electrode materials for the electrochemical energy storage devices. However, their electrochemical performance including the capacitance and rate capability was greatly hindered due to ion penetrating long distances into the bulk regimes during the electrochemical process. Herein, low-crystalline birnessite-MnO2 nanograins are obtained, which can enhance the ion diffusion kinetics and electrochemical activity significantly due to the structural disorder and defects. The resultant electrode features a superior electrochemical performance with an areal capacitance up to 1154 mF/cm² at 2 mA/cm² and rate retention of 69 % when the current density increasing 10 times to 20 mA/cm² with a commercial standard mass loading about 4.58 mg/cm². And the cycle stability measurement shows no attenuation after 10000-cycle charge/discharge operation. Moreover, assembled asymmetric supercapacitor device (wide operation voltage of 2.3 V) delivers a maximum areal energy density of 0.36 mWh/cm² with the areal power density of 5.57 mW/cm². The electrochemical behavior studies and in-situ Raman reveal that the structural disorder in the low-crystalline nanograins greatly facilitate the reversible ion intercalation/deintercalation process during the electrochemical cycling process. Our results will provide an instructive route for the formulation of the design principle for the high-performance of transition metal oxides electrode material.
Increasing power and energy demands for next-generation portable and flexible electronics such as roll-up displays, photovoltaic cells, and wearable devices have stimulated intensive efforts to explore flexible, lightweight and environmentally friendly energy storage devices. Flexible solid-state supercapacitors (SCs) have attracted increasing interest because they can provide substantially higher specific/volumetric energy density compared to conventional capacitors. Additionally, flexible solid-state SCs are typically small in size, highly reliable, light-weight, easy to handle, and have a wide range of operation temperatures. In this regard, solid-state SCs hold great promise as new energy storage devices for flexible and wearable electronics. In this article, we review recent achievements in the design, fabrication and characterization of flexible solid-state SCs. Moreover, we also discuss the current challenges and future opportunities for the development of high-performance flexible solid-state SCs.
To push the energy density limit of supercapacitors, a new class of electrode materials with favorable architectures is strongly needed. Binary metal sulfides hold great promise as an electrode material for high-performance energy storage devices because they offer higher electrochemical activity and higher capacity than mono-metal sulfides. Here, the rational design and fabrication of NiCo2S4 nanosheets supported on nitrogen-doped carbon foams (NCF) is presented as a novel flexible electrode for supercapacitors. A facile two-step method is developed for growth of NiCo2S4 nanosheets on NCF with robust adhesion, involving the growth of Ni-Co precursor and subsequent conversion into NiCo2S4 nanosheets through sulfidation process. Benefiting from the compositional features and 3D electrode architectures, the NiCo2S4/NCF electrode exhibits greatly improved electrochemical performance with ultrahigh capacitance (877 F g−1 at 20 A g−1) and excellent cycling stability. Moreover, a binder-free asymmetric supercapacitor device is also fabricated by using NiCo2S4/NCF as the positive electrode and ordered mesoporous carbon (OMC)/NCF as the negative electrode; this demonstrates high energy density (≈45.5 Wh kg−1 at 512 W kg−1).
Asymmetric supercapacitors (ASCs) with high energy density are assembled based on the pseudocapacitance of both electrodes, which use polyaniline (PANI) nanotubes as positive electrodes and MoO3 nanobelts as negative electrodes in a 1 M H2SO4 aqueous electrolyte. The assembled novel PANI//MoO3 ASC device with an extended operating voltage window of 2.0 V, in spite of the use of an aqueous electrolyte, exhibits excellent performance such as a high specific capacitance of 518 F g−1 at a current density of 0.5 A g−1, reaching an energy density as high as 71.9 W h kg−1 at a power density of 254 W kg−1 and good cycling stability.
Graphene-bismuth oxide nanotube fiber as electrode material for constituting flexible supercapacitors using a PVA/H3PO4 gel electrolyte is reported with a high specific capacitance (Ca) of 69.3 mF cm(-2) (for a single electrode) and 17.3 mF cm(-2) (for the whole device) at 0.1 mA cm(-2), respectively. Our approach opens the door to metal oxide-graphene hybrid fibers and high-performance flexible electronics.
Flexible energy-storage devices are attracting increasing attention as they show unique promising advantages, such as flexibility, shape diversity, light weight, and so on; these properties enable applications in portable, flexible, and even wearable electronic devices, including soft electronic products, roll-up displays, and wearable devices. Consequently, considerable effort has been made in recent years to fulfill the requirements of future flexible energy-storage devices, and much progress has been witnessed. This review describes the most recent advances in flexible energy-storage devices, including flexible lithium-ion batteries and flexible supercapacitors. The latest successful examples in flexible lithium-ion batteries and their technological innovations and challenges are reviewed first. This is followed by a detailed overview of the recent progress in flexible supercapacitors based on carbon materials and a number of composites and flexible micro-supercapacitors. Some of the latest achievements regarding interesting integrated energy-storage systems are also reviewed. Further research direction is also proposed to surpass existing technological bottle-necks and realize idealized flexible energy-storage devices.
The integration of graphene nanosheets on the macroscopic level using a self-assembly method has been recognized as one of the most effective strategies to realize the practical applications of graphene materials. Here, a facile and scalable method is developed to synthesis two types of graphene-based networks, manganese dioxide (MnO2)–graphene foam and carbon nanotube (CNT)–graphene foam, by solution casting and subsequent electrochemical methods. Their practical applications in flexible all-solid-state asymmetric supercapacitors are explored. The proposed method facilitates the structural integration of graphene foam and the electroactive material and offers several advantages including simplicity, efficiency, low-temperature, and low-cost. The as-prepared MnO2–graphene and CNT–graphene electrodes exhibit high specific capacitances and rate capability. By using polymer gel electrolytes, a flexible all-solid-state asymmetric supercapacitor was synthesized with MnO2–graphene foam as the positive electrode and CNT-graphene as the negative electrode. The asymmetric supercapacitors can be cycled reversibly in a high-voltage region of 0 to 1.8 V and exhibit high energy density, remarkable rate capability, reasonable cycling performance, and excellent flexibility.
Asymmetric supercapacitors with high energy density are fabricated using a self-assembled reduced graphene oxide (RGO)/MnO2 (GrMnO2) composite as a positive electrode and a RGO/MoO3 (GrMoO3) composite as a negative electrode in safe aqueous Na2SO4 electrolyte. The operation voltage is maximized by choosing two metal oxides with the largest work function difference. Because of the synergistic effects of highly conductive graphene and highly pseudocapacitive metal oxides, the hybrid nanostructure electrodes exhibit better charge transport and cycling stability. The operation voltage is expanded to 2.0 V in spite of the use of aqueous electrolyte, revealing a high energy density of 42.6 Wh kg−1 at a power density of 276 W kg−1 and a maximum specific capacitance of 307 F g−1, consequently giving rise to an excellent Ragone plot. In addition, the GrMnO2//GrMoO3 supercapacitor exhibits improved capacitance with cycling up to 1000 cycles, which is explained by the development of micropore structures during the repetition of ion transfer. This strategy for the choice of metal oxides provides a promising route for next-generation supercapacitors with high energy and high power densities.
A high performance asymmetric electrochemical supercapacitor with a mass loading of 10 mg·cm−2 on each planar electrode has been fabricated by using a graphene-nickel cobaltite nanocomposite (GNCC) as a positive electrode and commercial activated carbon (AC) as a negative electrode. Due to the rich number of faradaic reactions on the nickel cobaltite, the GNCC positive electrode shows significantly higher capacitance (618 F·g−1) than graphene-Co3O4 (340 F·g−1) and graphene-NiO (375 F·g−1) nanocomposites synthesized under identical conditions. More importantly, graphene greatly enhances the conductivity of nickel cobaltite and allows the positive electrode to charge/discharge at scan rates similar to commercial AC negative electrodes. This improves both the energy density and power density of the asymmetric cell. The asymmetric cell composed of 10 mg GNCC and 30 mg AC displayed an energy density in the range of 19.5 Wh·kg−1 with an operational voltage of 1.4 V. At high sweep rate, the system is capable of delivering an energy density of 7.6 Wh·kg−1 at a power density of about 5600 W·kg−1. Cycling results demonstrate that the capacitance of the cell increases to 116% of the original value after the first 1600 cycles due to a progressive activation of the electrode, and maintains 102% of the initial value after 10000 cycles.
Core/shell nanostructures often exhibit novel physical and chemical properties. Herein ZnO@MoO3 core/shell nanocables have been synthesized in large quantities by a simple electrochemical method at room temperature and the shell thickness of MoO3 can be controlled by changing the deposition time. The synthesized core/shell nanocables were characterized by scanning electron microscopy (SEM), transmission electron microscopy (TEM), X-ray diffraction (XRD), and X-ray photoelectron spectroscopy (XPS). The inner ZnOnanorod shows a single-crystal structure and has preferential growth in the [0001] direction. The MoO3 shell also shows a single-crystal structure with a [0001] direction. The prepared ZnO@MoO3 core/shell nanocables have been successfully employed as supercapacitor electrodes and give a specific capacitance of 236 F g−1 at scan rate of 5 mV s−1, which is much larger than that of MoO3nanoparticles. In addition, ZnO@ MoO3 core/shell nanocables show high electrochemical stability and can withstand over 1000 cycles with no obvious decrease in the specific capacitance.
In this paper, we reported an effective and simple strategy to prepare large areal mass loading of MnO2 on porous graphene gel/Ni foam (denoted as MnO2/G-gel/NF) for supercapacitors (SCs). The MnO2/G-gel/NF (MnO2 mass: 13.6 mg cm(-2)) delivered a large areal capacitance of 3.18 F cm(-2) (234.2 F g(-1)) and good rate capability. The prominent electrochemical properties of MnO2/G-gel/NF are attributed to the enhanced conductivities and improved accessible area for ions in electrolytes. Moreover, an asymmetric supercapacitor (ASC) based on MnO2/G-gel/NF (MnO2 mass: 6.1 mg cm(-2)) as the positive electrode and G-gel/NF as the negative electrode achieved a remarkable energy density of 0.72 mW h cm(-3). Additionally, the fabricated ASC device also exhibited excellent cycling stability, with less than 1.5% decay after 10 000 cycles. The ability to effectively develop SC electrodes with high mass loading should open up new opportunities for SCs with high areal capacitance and high energy density.
A new kind of high-performance asymmetric supercapacitor is designed with pyrolyzed bacterial cellulose (p-BC)-coated MnO2 as a positive electrode material and nitrogen-doped p-BC as a negative electrode material via an easy, efficient, large-scale, and green fabrication approach. The optimal asymmetric device possesses an excellent supercapacitive behavior with quite high energy and power density.
An asymmetric supercapacitor with high energy and power densities has been fabricated using MnO2/carbon nanofiber composites as positive electrode and activated carbon nanofibers as negative electrode in Na2SO4 aqueous electrolyte. Both electrode materials are freestanding in nature without any conductive additives or binders and exhibit outstanding electrochemical performances. The as-assembled asymmetric supercapacitor with optimal mass ratio can be operated reversibly over a wide voltage range of 0-2.0 V, and presents a maximum energy density of 30.6 Wh kg(-1), which is much higher than those of symmetric supercapacitors. More-over, the supercapacitor exhibits excellent rate capability (high power density of 20.8 kW kg(-1) at 8.7 Wh kg(-1)) and long-term cycling stability with only 6% loss of its initial capacitance after 5000 cycles. These attractive results make these freestanding materials promising for applications in aqueous electrolyte-based asymmetric supercapacitors with high energy and power densities delivery.
A flexible solid-state asymmetric supercapacitor based on bendable film electrodes with 3D expressway-like architecture of graphenes and “hard nano-spacer” is fabricated via an extended filtration assisted method. In the designed structure of the positive electrode, graphene sheets are densely packed, and Ni(OH)2 nanoplates are intercalated in between the densely stacked graphenes. The 3D expressway-like electrodes exhibit superior supercapacitive performance including high gravimetric capacitance (≈573 F g-1), high volumetric capacitance (≈655 F cm-3), excellent rate capability, and superior cycling stability. In addition, another hybrid film of graphene and carbon nanotubes (CNT) is fabricated as the negative electrodes for the designed asymmetric device. In the obtained graphene@CNT films, CNTs served as the hard spacer to prevent restacking of graphene sheets but also as a conductive and robust network to facilitate the electrons collection/transport in order to fulfill the demand of high-rate performance of the asymmetric supercapacitor. Based on these two hybrid electrode films, a solid-state flexible asymmetric supercapacitor device is assembled, which is able to deliver competitive volumetric capacitance of 58.5 F cm-3 and good rate capacity. There is no obvious degradation of the supercapacitor performance when the device is in bending configuration, suggesting the excellent flexibility of the device.
A hierarchical nanostructure composed of NiMn-layered double hydroxide (NiMn-LDH) microcrystals grafted on carbon nanotube (CNT) backbone is constructed by an in situ growth route, which exhibits superior supercapacitive performance. The resulting composite material (NiMn-LDH/CNT) displays a three-dimensional architecture with tunable Ni/Mn ratio, well-defined core-shell configuration, and enlarged surface area. An electrochemical investigation shows that the Ni3Mn1-LDH/CNT electrode is rather active, which delivers a maximum specific capacitance of 2960 F g–1 (at 1.5 A g–1), excellent rate capability (79.5% retention at 30 A g–1), and cyclic stability. Moreover, an all-solid-state asymmetric supercapacitor (SC) with good flexibility is fabricated by using the NiMn-LDH/CNT film and reduced graphene oxide (RGO)/CNT film as the positive and negative electrode, respectively, exhibiting a wide cell voltage of 1.7 V and largely enhanced energy density up to 88.3 Wh kg–1 (based on the total weight of the device). By virtue of the high-capacity of pseudocapacitive hydroxides and desirable conductivity of carbon-based materials, the monolithic design demonstrated in this work provides a promising approach for the development of flexible energy storage systems.
Owing to the rapidly growing global energy consumption, the development of high-performance power sources has become an urgent and increasing demand in various fi elds such as port-able electronics and sensor networks. [ 1–3 ] As a result of their excellent characteristics, such as superior power density, fast charge/discharge rates, and long cycle lifetime, supercapacitors (SCs, also known as electrochemical capacitors or ultracapaci-tors), which bridge the gap between high specifi c energy bat-teries and high specifi c power conventional capacitors, have been employed as state-of-the-art energy storage systems and widely used in consumer electronics, backup power sources, and pacemakers. [ 4–7 ] Since the energy density is proportional to the capacitance (specifi c or areal capacitance), C , and square of the cell voltage, Δ U , which can be calculated as E = 0.5C(U)
A facile and novel one‐step method of growing nickel‐cobalt layered double hydroxide (Ni‐Co LDH) hybrid films with ultrathin nanosheets and porous nanostructures on nickel foam is presented using cetyltrimethylammonium bromide as nanostructure growth assisting agent but without any adscititious alkali sources and oxidants. As pseudocapacitors, the as‐obtained Ni‐Co LDH hybrid film‐based electrodes display a significantly enhanced specific capacitance (2682 F g−1 at 3 A g−1, based on active materials) and energy density (77.3 Wh kg−1 at 623 W kg−1), compared to most previously reported electrodes based on nickel‐cobalt oxides/hydroxides. Moreover, the asymmetric supercapacitor, with the Ni‐Co LDH hybrid film as the positive electrode material and porous freeze‐dried reduced graphene oxide (RGO) as the negative electrode material, exhibits an ultrahigh energy density (188 Wh kg−1) at an average power density of 1499 W kg−1 based on the mass of active material, which greatly exceeds the energy densities of most previously reported nickel or cobalt oxide/hydroxide‐based asymmetric supercapacitors. Ni–Co LDH electrode materials with ultrahigh capacitive performance are prepared. The capacitive performances of as‐obtained Ni–Co LDHs for pseudocapacitors and asymmetric supercapacitors significantly exceed those of most similar reported materials. This synthesis method can also be extended to synthesize other bimetallic LDHs with high electrochemical activity.
A simple one-step electroplating route is proposed for the synthesis of novel iron oxyhydroxide lepidocrocite (γ-FeOOH) nanosheet anodes with distinct layered channels, and the microstructural influence on the pseudocapacitive performance of the obtained γ-FeOOH nanosheets is investigated via in situ X-ray absorption spectroscopy (XAS) and electrochemical measurement. The in situ XAS results regarding charge storage mechanisms of electrodeposited γ-FeOOH nanosheets show that a Li+ can reversibly insert/desert into/from the 2D channels between the [FeO6] octahedral subunits depending on the applied potential. This process charge compensates the Fe2+/Fe3+ redox transition upon charging–discharging and thus contributes to an ideal pseudocapacitive behavior of the γ-FeOOH electrode. Electrochemical results indicate that the γ-FeOOH nanosheet shows the outstanding pseudocapacitive performance, which achieves the extraordinary power density of 9000 W kg−1 with good rate performance. Most importantly, the asymmetric supercapacitors with excellent electrochemical performance are further realized by using 2D MnO2 and γ-FeOOH nanosheets as cathode and anode materials, respectively. The obtained device can be cycled reversibly at a maximum cell voltage of 1.85 V in a mild aqueous electrolyte, further delivering a maximum power density of 16 000 W kg−1 at an energy density of 37.4 Wh kg−1.
Vanadium pentoxide–reduced graphene oxide (rGO) free-standing electrodes are used as electrodes for supercapacitor applications, eliminating the need for current collectors or additives and reducing resistance (sheet resistance 29.1 Ω □−1). The effective exfoliation of rGO allows improved electrolyte ions interaction, achieving high areal capacitance (511.7 mF cm−2) coupled with high mass loadings. A fabricated asymmetric flexible device based on rGO/V2O5-rGO (VGO) consists of approximately 20 mg of active mass and still delivers a low equivalent series resistance (ESR) of 3.36 Ω with excellent cycling stability. A prototype unit of the assembled device with organic electrolyte is shown to light up eight commercial light-emitting diode bulbs.
The electrochemical performance of supercapacitors relies not only on the exploitation of high-capacity active materials, but also on the rational design of superior electrode architectures. Herein, a novel supercapacitor electrode comprising 3D hierarchical mixed-oxide nanostructured arrays (NAs) of C/CoNi3O4 is reported. The network-like C/CoNi3O4 NAs exhibit a relatively high specific surface area; it is fabricated from ultra-robust Co-Ni hydroxide carbonate precursors through glucose-coating and calcination processes. Thanks to their interconnected three-dimensionally arrayed architecture and mesoporous nature, the C/CoNi3O4 NA electrode exhibits a large specific capacitance of 1299 F/g and a superior rate performance, demonstrating 78% capacity retention even when the discharge current jumps by 100 times. An optimized asymmetric supercapacitor with the C/CoNi3O4 NAs as the positive electrode is fabricated. This asymmetric supercapacitor can reversibly cycle at a high potential of 1.8 V, showing excellent cycling durability and also enabling a remarkable power density of ∼13 kW/kg with a high energy density of ∼19.2 W·h/kg. Two such supercapacitors linked in series can simultaneously power four distinct light-emitting diode indicators; they can also drive the motor of remote-controlled model planes. This work not only presents the potential of C/CoNi3O4 NAs in thin-film supercapacitor applications, but it also demonstrates the superiority of electrodes with such a 3D hierarchical architecture.
Bacterial cellulose (BC) is used as both template and precursor for the synthesis of nitrogen-doped carbon networks through the carbonization of polyaniline (PANI) coated BC. The as-obtained carbon networks can act not only as support for obtaining high capacitance electrode materials such as activated carbon (AC) and carbon/MnO2 hybrid material, but also as conductive networks to integrate active electrode materials. As a result, the as-assembled AC//carbon-MnO2 asymmetric supercapacitor exhibits a considerably high energy density of 63 Wh kg−1 in 1.0 m Na2SO4 aqueous solution, higher than most reported AC//MnO2 asymmetric supercapacitors. More importantly, this asymmetric supercapacitor also exhibits an excellent cycling performance with 92% specific capacitance retention after 5000 cycles. Those results offer a low-cost, eco-friendly design of electrode materials for high-performance supercapacitors.
In this paper, a highly ordered three-dimensional Co3O4@MnO2 hierarchical porous nanoneedle array on nickel foam is fabricated by a facile, stepwise hydrothermal approach. The morphologies evolution of Co3O4 and Co3O4@MnO2 nanostructures upon reaction times and growth temperature are investigated in detail. Moreover, the as-prepared Co3O4@MnO2 hierarchical structures are investigated as anodes for both supercapacitors and Li-ion batteries. When used for supercapacitors, excellent electrochemical performances such as high specific capacitances of 932.8 F g−1 at a scan rate of 10 mV s−1 and 1693.2 F g−1 at a current density of 1 A g−1 as well as long-term cycling stability and high energy density (66.2 W h kg−1 at a power density of 0.25 kW kg−1), which are better than that of the individual component of Co3O4 nanoneedles and MnO2 nanosheets, are obtained. The Co3O4@MnO2 NAs are also tested as anode material for LIBs for the first time, which presents an improved performance with high reversible capacity of 1060 mA h g−1 at a rate of 120 mA g−1, good cycling stability, and rate capability.
Oxygen-deficient α-Fe2 O3 nanorods with outstanding capacitive performance are developed and demonstrated as novel negative electrodes for flexible asymmetric supercapacitors. The asymmetric-supercapacitor device based on the oxygen-deficient α-Fe2 O3 nanorod negative electrode and a MnO2 positive electrode achieves a maximum energy density of 0.41 mW·h/cm(3) ; it is also capable of charging a mobile phone and powering a light-emitting diode indicator.
Porous carbon nanofibers (CNFs) derived from graphene oxide (GO) were prepared from the carbonization of electrospun polyacrylonitrile nanofibers with up to 15 wt.% GO at 1200 °C, followed by a low-temperature activation. The activated CNFs with reduced GOs (r-GO) revealed a specific surface area and adsorption capacity of 631 m2/g and 191.2 F/g, respectively, which are significantly higher than those of pure CNFs (16 m2/g and 3.1 F/g). It is believed that rough interfaces between r-GO and CNFs introduce oxygen pathways during activation, help to produce large amounts of all types of pores compared to pure activated CNFs.
A low-cost high-performance solid-state flexible asymmetric supercapacitor (ASC) with α-MnO2 nanowires and amorphous Fe2O3 nanotubes grown on flexible carbon fabric is firstly designed and fabricated. The assembled novel flexible ASC device with an extended operating voltage window of 1.6 V exhibits excellent performance such as a high energy density of 0.55 mWh/cm3 and good rate capability. The ASC devices can find numerous applications as effective power sources, such as powering color-switchable sun glasses and smart windows.
This paper presents highly conductive carbon nanofiber/MnO2 coaxial cables in which individual electrospun carbon nanofibers are coated with an ultrathin hierarchical MnO2 layer. In the hierarchical MnO2 structure, an around 4 nm thick sheath surrounds the carbon nanofiber (CNF) in a diameter of 200 nm, and nano-whiskers grow radically outward from the sheath in view of the cross-section of the coaxial cables, giving a high specific surface area of MnO2. The CNFs are synthesized by electrospinning a precursor containing iron acetylacetonate (AAI). The addition of AAI not only enlarges the specific surface area of the CNF but also greatly enhances their electronic conductivity, which leads to a dramatic improvement in the specific capacitance and the rate capability of the CNF/MnO2 electrode. The AAI-CNF/MnO2 electrode shows a specific capacitance of 311 F g−1 for the whole electrode and 900 F g−1 for the MnO2 shell at a scan rate of 2 mV s−1. Good cycling stability, high energy density (80.2 Wh kg−1) and high power density (57.7 kW kg−1) are achieved. This work indicates that high electronic conductivity of the electrode material is crucial to achieving high power and energy density for pseudo-supercapacitors.
An advanced electrode for high-performance electrochemical capacitors has been designed by growing ultrathin mesoporous Co3O4 nanosheet arrays on the Ni foam support. This unique 3D electrode manifests exceptional supercapacitive performance with ultrahigh specific capacitance at high current densities and excellent cycling stability.
The Kirkendall effect has gained intense attention and wide acceptance in nanoscience and nanotechnology because it can result in porosity or deformation in the case of the alloying or oxidation of metals. In this work, we report a facile approach to prepare δ-Bi2O3 solid spheres and further convert them to hierarchical BiOI nests for the first time through a solvothermal reaction at low temperature. The δ-Bi2O3 and BiOI samples obtained were characterized by scanning electron microscopy (SEM), transmission electron microscopy (TEM), X-ray powder diffraction (XRD) and X-ray photoelectron spectroscopy (XPS). The formation mechanism has been proposed by emphasizing the Kirkendall effect. We also found that the template of δ-Bi2O3 solid spheres was initially formed by surfactantoleylamine induction. Anion exchange has been confirmed to occur in the reaction involving the Kirkendall effect.
A novel cable-type flexible supercapacitor with excellent performance is fabricated using 3D polypyrrole(PPy)-MnO2 -CNT-cotton thread multi-grade nanostructure-based electrodes. The multiple supercapacitors with a high areal capacitance 1.49 F cm(-2) at a scan rate of 1 mV s(-1) connected in series and in parallel can successfully drive a LED segment display. Such an excellent performance is attributed to the cumulative effect of conducting single-walled carbon nanotubes on cotton thread, active mesoporous flower-like MnO2 nanoplates, and PPy conductive wrapping layer improving the conductivity, and acting as pseudocapacitance material simultaneously.
Carbon nanofibers (CNFs)/MnO2 nanocomposites were prepared as freestanding electrodes using in situ redox deposition and electrospinning. The electrospun CNFs substrates with porosity and interconnectivity enabled the uniform incorporation of birnessite-type MnO2 deposits on each fiber, thus showing unique and conformal coaxial nanostructure. CNFs not only provided considerable specific surface area for high mass loading of MnO2 but also offered reliable electrical conductivity to ensure the full utilization of MnO2 coatings. The effect of MnO2 loading on the electrochemical performances was investigated by cyclic voltammetry (CV), impedance measurements and Galvonostatic charging/discharging technique. The results showed that an ultrathin MnO2 deposits were indispensable to achieve better electrochemical performance. The maximum specific capacitance (based on pristine MnO2) attained to 557F/g at a current density of 1A/g in 0.1M Na2SO4 electrolyte when the mass loading reached 0.33mg/cm2. This freestanding electrode also exhibited good rate capability (power density of 13.5kW/kg and energy density of 20.9Wh/kg at 30A/g) and long-term cycling stability (retaining 94% of its initial capacitance after 1500 cycles). These characteristics suggested that such freestanding CNFs/MnO2 nanocomposites are promising for high-performance supercapacitors.
We have prepared NiO particles on Ni sheet and Ni foam substrates by chemical bath deposition and the following heat-treatment, and assembled a hybrid capacitor (HC) cell with the NiO-loaded Ni sheet or Ni foam positive electrode and activated carbon negative electrode. The deposited NiO particles had flower-like porous morphology which was composed of aggregated nanosheets. The maximum operating voltage of both HC cells was 1.5V, which was much higher than theoretical decomposition voltage of water (1.23V). The HC cell with NiO/Ni foam (HCfoam) had higher discharge capacitance and high-rate dischargeability and lower IR drop than the HC cell with NiO/Ni sheet (HCsheet) because of the increase in the utilization of NiO active material. Both energy and power densities per mass of active materials, were much higher than those for the HCsheet. Both HCfoam and HCsheet showed excellent cycle stability for 2000 cycles.
Bismuth oxide (Bi2O3) thin films are grown on copper substrates at room temperature by electrodeposition from an aqueous alkaline nitrate bath. The usefulness of electrochemically deposited Bi2O3 for electrochemical supercapacitors is proposed for the first time. The supercapacitor properties of Bi2O3 electrode are studied in aqueous NaOH solution. The Bi2O3 electrode exhibits very good electrochemical supercapacitive characteristics as well as stability in aqueous NaOH electrolyte. The effect of electrolyte concentration, scan rate, and number of cycles on the specific capacitance of Bi2O3 electrodes has been studied. The highest specific capacitance achieved with the electrodeposited Bi2O3 films is 98Fg−1.
Manganese oxide (MnO x) thin films were deposited on transparent conducting tin oxide glass substrates by potentiostatic anodic electrolysis of alkaline solution of a manganese ammine complex at 298 K. The effects of varying deposition potentials on the microstructure and the electrochromic (EC) properties of the films were investigated. Characterization of films by X-ray diffraction revealed that two distinct potential regions (lower and higher than 0.3 V vs. Ag/AgCl) were available for the film deposition; the crystal structure of the film deposited at lower and higher regions were γ-Mn 2O 3 and/or Mn 3O 4 and Mn 7O 13·5H 2O, respectively. X-ray photoelectron spectroscopy (XPS) analyses of the films featuring exchange splitting effect on Mn 3s spectra indicated that the valence of manganese in the films prepared at lower and higher potential regions are mixtures of divalence-trivalence and of trivalence-tetravalence, respectively. The XPS analysis also revealed that terminal chemical bonding species of the films are a mixture of hydroxide (Mn-O-H) and oxide (Mn-O-Mn). The mechanism of the EC process, by which the color change between brown and light yellow occurs, could be explained in terms of the transformation between these two oxygen groups in Mn-O-H and Mn-O-Mn, accompanied by the change in valence of Mn. The EC durability of the films in switching performance was also assessed.