Highly flexible supercapacitors (SCs) have great potential in modern electronics such as wearable and portable devices. However, ultralow specific capacity and low operating potential window limit ...their practical applications. Herein, a new strategy for the fabrication of free‐standing NiMoS and NiFeS nanosheets (NSs) for high‐performance flexible asymmetric SC (ASC) through hydrothermal and subsequent sulfurization technique is reported. The effect of Ni2+ is optimized to attain hierarchical NiMoS and NiFeS NS architectures with high electrical conductivity, large surface area, and exclusive porous networks. Electrochemical properties of NiMoS and NiFeS NS electrodes exhibit that both have ultrahigh specific capacities (≈312 and 246 mAh g−1 at 1 mA cm−2), exceptional rate capabilities (78.85% and 78.46% capacity retention even at 50 mA cm−2, respectively), and superior cycling stabilities. Most importantly, a flexible NiMoS NS//NiFeS NS ASC delivers a high volumetric capacity of ≈1.9 mAh cm−3, excellent energy density of ≈82.13 Wh kg−1 at 0.561 kW kg−1, exceptional power density (≈13.103 kW kg−1 at 61.51 Wh kg−1) and an outstanding cycling stability, retaining ≈95.86% of initial capacity after 10 000 cycles. This study emphasizes the potential importance of compositional tunability of the NS architecture as a novel strategy for enhancing the charge storage properties of active electrodes.
The present investigation demonstrates a novel strategy for the fabrication of free‐standing NiMoS and NiFeS nanosheets (NS) through a cost‐effective hydrothermal technique with subsequent sulfurization. Flexible NiMoS NS//NiFeS NS asymmetric supercapacitor delivers an ultrahigh energy density of ≈82.13 Wh kg−1 at 0.561 kW kg−1, and outstanding cycling stability, retaining ≈95.86% of the initial capacity after 10 000 cycles.
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•Preparation of CdS-based photocatalysts by a hydrothermal method.•Production of hydrogen peroxide from water and oxygen.•Temperature- and pH-dependent production of hydrogen ...peroxide.
We demonstrate the sustainable production of H2O2 without organic electron donors by a CdS-reduced graphene oxide (RGO) photocatalyst in sunlight with water and oxygen as resources. Photocatalysts were prepared with various amounts of RGO (0–30wt.% with respect to CdS) by a hydrothermal method. A photocatalyst containing 20wt.% RGO (CdS-G2) showed maximum activity, and the amount of H2O2 produced (128μM) was almost five times higher than that produced by CdS nanoparticles (27μM) after 12h sunlight irradiation. The results clearly revealed that the photocatalytic reactionmainly proceeds by two-electron reduction of oxygenrather than water oxidation on the catalyst surface. The effects of reaction temperature and pH on the production of H2O2 were also investigated. We found that the production of H2O2was enhanced at lower temperature and pH. The concentration of H2O2 reachedto 164 and 156μM with CdS-G2 at 10°C and pH 2, respectively.
A facile two‐step strategy is developed to design the large‐scale synthesis of hierarchical, unique porous architecture of ternary metal hydroxide nanowires grown on porous 3D Ni foam and subsequent ...effective sulfurization. The hierarchical Zn–Co–S nanowires (NWs) arrays are directly employed as an electrode for supercapacitors application. The as‐synthesized Zn–Co–S NWs deliver an ultrahigh areal capacity of 0.9 mA h cm−2 (specific capacity of 366.7 mA h g−1) at a current density of 3 mA cm−2, with an exceptional rate capability (≈227.6 mA h g−1 at a very high current density of 40 mA cm−2) and outstanding cycling stability (≈93.2% of capacity retention after 10 000 cycles). Most significantly, the assembled Zn–Co–S NWs//Fe2O3@reduced graphene oxide asymmetric supercapacitors with a wide operating potential window of ≈1.6 V yield an ultrahigh volumetric capacity of ≈1.98 mA h cm−3 at a current density of 3 mA cm−2, excellent energy density of ≈81.6 W h kg−1 at a power density of ≈559.2 W kg−1, and exceptional cycling performance (≈92.1% of capacity retention after 10 000 cycles). This general strategy provides an alternative to design the other ternary metal sulfides, making it facile, free‐standing, binder‐free, and cost‐effective ternary metal sulfide‐based electrodes for large‐scale applications in modern electronics.
The present work demonstrates the construction of hierarchical Zn–Co–S nanowires (NWs) for high performance all solid state asymmetric supercapacitors. The Zn–Co–S NWs//Fe2O3@reduced graphene oxide asymmetric supercapacitor delivers an excellent energy density of ≈81.6 W h kg−1 at a power density of ≈559.2 W kg−1, and exceptional cycling performance (≈92.1% capacity retention after 10 000 cycles).
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•The 3D Zn-Ni-Co oxide@NiMoO4 nanostructure supported Ni foam electrode was made.•The electrode delivers excellent specific capacity of 0.98 mA h cm−2 at 3 mA cm−2.•The solid-state ...asymmetric supercapacitor shows an energy density of 70 W h kg−1.•The asymmetric supercapacitor shows high rate capability of 50.5% at 50 mA cm−2.•The capacitance retention of asymmetric supercapacitor is 91% after 10,000 cycles.
In the search for advanced positive pseudocapacitive electrode material for potential application to practical energy storage and conversion devices, innovative design and alteration of the assemblage of the complex transition metal oxide based core-shell heterostructures are technically highly essential undertakings. Herein, uniquely assembled three-dimensional porous Zn-Ni-Co oxide (ZNCO)@NiMoO4 core-shell nanowire/nanosheet arrays (NWNSAs) supported on Ni foam as integrated pseudocapacitive electrode are fabricated for the first time by a facile and scalable two-step hydrothermal process combined with post-annealing methods. Taking advantage of the synergistic interaction in core-shell architecture, the hierarchical porous ZNCO@NiMoO4 NWNSAs offers excellent conductivity, durability, effective nanoporous network, and proper channels for the rapid transfer of ions/electron for reversible Faradaic reaction. In a three-electrode assembly, the hierarchical as-synthesized ZNCO@NiMoO4 electrode exhibits higher specific capacity (CS; 338.5 mA h g−1 at 3 mA cm−2), rate performance (71% up to 25 mA cm−2), and good cyclic stability (86% capacity retention after 10,000 cycles) than the ZNCO electrode (CS; 266.1 mA h g−1 and 57% up to 25 mA cm−2). The all-solid-state asymmetric supercapacitor (ASC) device consisting of ZNCO@NiMoO4 NWNSAs as cathode and Fe2O3/graphene hydrogel as anode electrodes shows superior specific capacity (87.5 mA h g−1 at 4 mA cm−2), high rate capability (50.5% up to 50 mA cm−2), excellent life-span (91% after 10,000 GCD cycles), and very high energy and power densities (~70 W h kg−1 and 5115.1 W kg−1), suggesting its potential applicability to advanced hybrid supercapacitors.
A three-dimensional (3-D) porous structure was designed based on carbon dot (CD)-supported copper sulphide (CuS)-decorated graphene oxide (GO) hydrogel for using in a high-performance asymmetric ...supercapacitor device to improve the specific capacitance, cyclic stability and energy density of CuS as well as GO based supercapacitors. CD coated CuS (CuS@CD) decorated GO hydrogels (CuS@CD-GOH) were prepared by a simple hydrothermal reaction at 180 °C and optimized through different spectroscopic, diffraction, microscopic and electrochemical analyses. CD acted as a stabilizer for the CuS nanoparticles and help to bind strongly CuS nanoparticles with GO inside the 3-D hydrogel structure. The CuS@CD-GOH exhibited high specific capacitance of 920 F g−1 at a current density of 1 A g−1. The optimal CuS@CD-GOH was used as a positive electrode for the fabrication of asymmetric supercapacitor along with reduced GO as the negative electrode, which delivered the highest energy density up to 28 W h kg−1 along with long cycling life and retains up to 90% specific capacitance after 5000 cycles. The results are excellent in comparison to the reported CuS and composite GO hydrogel based supercapacitors. Thus, this work will provide a new insight of CuS and GO based composite 3-D structures for supercapacitor applications.
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Development of highly functional and durable catalysts in a cost-effective way is a promising approach for practical energy conversion applications. In this study, a novel catalyst, cobalt iron ...carbide nanoparticles encapsulated by nitrogen doped graphene nanosheets, is successfully synthesized through a simple refluxing strategy followed by a post annealing process. It is found that the catalyst exhibits excellent catalytic activity for oxygen reduction reaction in alkaline medium. The oxygen reduction reaction kinetics of the catalyst mainly follow a 4-electron transferred pathway along with good diffusion limit current density, highly positive onset potential (−0.04 V) and half-wave potential (−0.11 V). In addition to catalytic activity, the catalyst demonstrates advanced superior stability, and excellent methanol tolerance in comparison with commercial platinum catalyst. The impressive catalytic performance of the catalyst is attributed to the unique mesoporous metal-core/graphene-shell architecture in which high interactions between two transition metals and transition metal-carbon synergistically provide enhanced catalytically active sites, accelerate interfacial charge transfer, and optimize oxygen adsorption energy. The results demonstrate that such catalyst can be an alternative low-cost and efficient catalyst for oxygen reduction reaction in energy conversion applications.
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To meet a fast‐emerging demand, flexible energy storage applications have a great interest in the development of highly flexible hierarchical nanoarchitectures. Metal nitrides have recently been paid ...a significant interest as a promising electrode material for supercapacitors (SCs) owing to their high electrical conductivity, excellent redox properties, and outstanding mechanical strength. However, poor electrochemical stability seriously limits the commercialization possibilities. Herein, a novel strategy is presented for the synthesis of nitrogen‐doped graphene encapsulated with ultrasmall nickel–cobalt nitride (NiCo2N) and nickel–iron nitride (NiFeN) core–shell architectures that are explored as advanced electrodes for flexible solid‐state SC. The flexible NiCo2N@NG//NiFeN@NG asymmetric SC delivers an ultrahigh energy density of ≈94.93 Wh kg−1 at 0.79 kW kg−1, exceptional power density (≈74.67 Wh kg−1 at 39.53 kW kg−1), and ultralong cycle life (≈5.07% drop in initial capacity after 25 000 cycles). These results promote the core–shell hybrids that can be served as advanced supercapacitor materials for flexible energy storage applications.
A novel strategy for the synthesis of nitrogen‐doped graphene encapsulated nickel–cobalt nitride (NiCo2N) and nickel–iron nitride (NiFeN) core–shell architectures is demonstrated herein. The composites are explored as advanced electrodes for flexible asymmetric supercapacitors (ASCs). The flexible ASC delivers an ultrahigh energy density of ≈94.93 Wh kg−1 at 0.79 kW kg−1 and ultralong cycle life.
Hierarchical nanostructure, high electrical conductivity, extraordinary specific surface area, and unique porous architecture are essential properties in energy storage and conversion studies. A new ...type of hierarchical 3D cobalt encapsulated Fe3O4 nanosphere is successfully developed on N‐graphene sheet (Co−Fe3O4 NS@NG) hybrid with unique nanostructure by simple, scalable, and efficient solvothermal technique. When applied as an electrode material for supercapacitors, hierarchical Co−Fe3O4 NS@NG hybrid shows an ultrahigh specific capacitance (775 F g−1 at a current density of 1 A g−1) with exceptional rate capability (475 F g−1 at current density of 50 A g−1), and admirable cycling performance (97.1% capacitance retention after 10 000 cycles). Furthermore, the fabricated Co−Fe3O4 NS@NG//CoMnO3@NG asymmetric supercapacitor (ASC) device exhibits a high energy density of 89.1 Wh kg−1 at power density of 0.901 kW kg−1, and outstanding cycling performance (89.3% capacitance retention after 10 000 cycles). Such eminent electrochemical properties of the Co−Fe3O4 NS@NG are due to the high electrical conductivity, ultrahigh surface area, and unique porous architecture. This research first proposes hierarchical Co−Fe3O4 NS@NG hybrid as an ultrafast charge−discharge anode material for the ASC device, that holds great potential for the development of high‐performance energy storage devices.
A hierarchical 3D Co−Fe3O4 NS@NG hybrid is successfully fabricated by a one‐step solvothermal method and used as an anode for high‐energy asymmetric supercapacitors (ASCs). The fabricated CoMnO3@NG//Co‐Fe3O4 NS@NG ASC delivers ultrahigh energy density of 89.1 Wh kg−1 at power density of 901 W kg−1.
Nitrogen (N)-doped graphene (NG) sheets were prepared using (NH4)2CO3 and an aqueous dispersion of graphene oxide (GO) by an eco-friendly hydrothermal reaction. The in situ produced ammonia played an ...important role in the simultaneous nitrogen doping, the reduction and exfoliation of GO. The (NH4)2CO3/GO mass ratio and reaction temperature were varied to investigate the effects on the N doping level. The elemental analysis determined from the X-ray photoelectron spectroscopy showed that the nitrogen content of the NG was about 10.1at.% and the oxygen content decreased significantly due to the hydrothermal reduction of GO. The electrochemical performances of the NG sheets increased with increasing doped N content. The highest specific capacitance of 295Fg−1 at a current density of 5Ag−1 and the highest specific surface area of 412m2g−1 were observed with the sample processed at 130°C. The retention of the specific capacitance was maintained at ∼89.8% after 5000 charge–discharge cycles. These results imply that NG sheets obtained by this simple eco-friendly approach are suitable for use in high performance energy storage electrode materials.
