Amorphous nickel-based hydroxides with different cation substitutions for advanced hybrid supercapacitors

Self-supported bimetallic array superstructures for high-performance coupling electrosynthesis of formate and adipate

The coupling electrosynthesis involving CO2 upgrade conversion is of great significance for the sustainable development of the environment and energy but is challenging. Herein, we exquisitely constructed the self-supported bimetallic array superstructures from the Cu(OH)2 array architecture precursor, which can enable high-performance coupling electrosynthesis of formate and adipate at the anode and the cathode, respectively. Concretely, the faradaic efficiencies (FEs) of CO2-to-formate and cyclohexanone-to-adipate conversion simultaneously exceed 90% at both electrodes with excellent stabilities. Such high-performance coupling electrosynthesis is highly correlated with the porous nanosheet array superstructure of CuBi alloy as the cathode and the nanosheet-on-nanowire array superstructure of CuNi hydroxide as the anode. Moreover, compared to the conventional electrolysis process, the cell voltage is substantially reduced while maintaining the electrocatalytic performance for coupling electrosynthesis in the two-electrode electrolyzer with the maximal FEformate and FEadipate up to 94.2% and 93.1%, respectively. The experimental results further demonstrate that the bimetal composition modulates the local electronic structures, promoting the reactions toward the target products. Prospectively, our work proposes an instructive strategy for constructing adaptive self-supported superstructures to achieve efficient coupling electrosynthesis.

Amorphous Co-Mo-S nanospheres fabricated via room-temperature vulcanization for asymmetric supercapacitors

Ternary metal sulfides employed in supercapacitors exhibit better electrochemical performances than their counterpart oxides due to their superior conductivity. However, the insertion/extraction of electrolyte ions can lead to a significant volume change in electrode materials, which can result in poor cycling stability. Herein, novel amorphous Co-Mo-S nanospheres were fabricated through a facile room-temperature vulcanization method. It involves the conversion of crystalline CoMoO4 by reacting it with Na2S at room temperature. In addition to the conversion of the crystalline state into an amorphous structure with more grain boundaries, which is beneficial for the transport of electron/ion and can accommodate the volume change generated by the insertion/extraction of electrolyte ions, the production of more pores led to an increased specific surface area. The electrochemical results indicate that the as-prepared amorphous Co-Mo-S nanospheres had a specific capacitance of up to 2049.7F/g@1 A/g together with good rate capability. The amorphous Co-Mo-S nanospheres can be used as the cathode of supercapacitors and assembled with an activated carbon anode into an asymmetric supercapacitor possessing a satisfactory energy density of 47.6 Wh kg-1@1012.9 W kg-1. One of the prominent features exhibited by this asymmetric device is its remarkable cyclic stability, with a capacitance retention of 107% after 10,000 cycles.

Self-Supported Sheets-on-Wire CuO@Ni(OH)2/Zn(OH)2 Nanoarrays for High-Performance Flexible Quasi-Solid-State Supercapacitor

Transition metal hydroxides have attracted a lot of attention as the electrode materials for supercapacitors owing to their relatively high theoretical capacity, low cost, and facile preparation methods. However, their low intrinsic conductivity deteriorates their high-rate performance and cycling stability. Here, self-supported sheets-on-wire CuO@Ni(OH)2/Zn(OH)2 (CuO@NiZn) composite nanowire arrays were successfully grown on copper foam. The CuO nanowire backbone provided enhanced structural stability and a highly efficient electron-conducting pathway from the active hydroxide nanosheets to the current collector. The resulting CuO@NiZn as the battery-type electrode for supercapacitor application delivered a high capacity of 306.2 mAh g−1 at a current density of 0.8 A g−1 and a very stable capacity of 195.1 mAh g−1 at 4 A g−1 for 10,000 charge–discharge cycles. Furthermore, a quasi-solid-state hybrid supercapacitor (qss HSC) was assembled with active carbon, exhibiting 125.3 mAh g−1 at 0.8 A g−1 and a capacity of 41.6 mAh g−1 at 4 A g−1 for 5000 charge–discharge cycles. Furthermore, the qss HSC was able to deliver a high energy density of about 116.0 Wh kg−1. Even at the highest power density of 7.8 kW kg−1, an energy density of 20.5 Wh kg−1 could still be obtained. Finally, 14 red light-emitting diodes were lit up by a single qss HSC at different bending states, showing good potential for flexible energy storage applications.

Hierarchical bimetallic hydroxide/chalcogenide core-sheath microarrays for freestanding ultrahigh rate supercapacitors

Transition metal compounds (TMCs) either crystalline or amorphous exhibit specific advantages in electrochemical energy storage. To integrate their merits into one electrode, we have herein developed hierarchical bimetallic hydroxide/chalcogenide core-sheath microarrays on nickel foam (NF) for freestanding high-efficiency supercapacitors, wherein interior crystalline metal chalcogenides serve as highly conductive pivots and exterior amorphous bimetallic hydroxides provide rich ion diffusion channels. With the synergic effect of the unique structure and bimetallic composition, the as-prepared Ni(OH)₂-Co(OH)₂/NiSe-Ni₃S₂/NF electrode displays an ultrahigh areal specific capacitance of 19.01 F cm^-2 at 15 mA cm^-2, which can be retained as 6.01 F cm^-2 even at 125 mA cm^-2. To the best of our knowledge, such excellent tolerance of ultrafast ion insertion/extraction at high current density is rare among NF-based free-standing electrodes. The asymmetric supercapacitor by assembling with activated carbon as the negative electrode delivers a volumetric capacitance of 3.93 F cm^-3 at 30 mA cm^-2, corresponding to an energy density of 13.9 mW h cm^-3 at a power density of 200 mW cm^-3. A capacitance retention of 82.5% was observed after 4000 cycles, together with an average 97% coulombic efficiency. This work may provide a facile strategy to construct hierarchical microarrays for efficient energy storage devices.