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Abstract: Ni(OH)2 nanosheets are directly grown on nickel foam by a simple template-free growth process. Their microstructure and surface morphology are studied by X-ray diffraction spectroscopy and scanning electron microscopy. The XRD and SEM results show that Ni(OH)2 has a β-phase structure and covers the nickel foam skeleton with nanosheets. This β-Ni(OH)2/Ni-foam electrode exhibits a high specific electric quantity of 790.3 C g−1 approaching the theoretical value (1040.6 C g−1) and high electrochemical activity. Asymmetric supercapacitor has been fabricated successfully using β-Ni(OH)2/Ni-foam nanosheets as positive electrode and activated carbon as negative electrode in a KOH aqueous electrolyte. The electrochemical capacitances of this supercapacitor are investigated by cyclic voltammetry, galvanostatic charge/discharge and electrochemical impedance spectroscopy. An asymmetric supercapacitor AC/6 mol L−1 KOH/β-Ni(OH)2/Ni-foam could be cycled reversibly in the high-voltage region of 0–1.6 V and displays intriguing performances with a specific capacitance of 105.8 F g−1 and high energy density of 36.2 W h kg−1. Importantly, this asymmetric supercapacitor device exhibits an excellent long cycle life along with 92% specific capacitance retained after 1000 cycles. [Copyright &y& Elsevier]

Developing novel materials with rational structures and excellent electrical conductivity is vitally important for energy storage devices. Herein, hollow cobalt molybdenum selenide (Co–Mo–Se) nanosheet arrays are fabricated via a self-sacrificing template method and selenization process, where cobalt-organic framework serves as the template. Benefiting from unique hollow nanoarrays structure, the Co–Mo–Se electrode offers rich electroactive sites, large accessible regions for electrolyte, and short ions diffusion pathways. Additionally, it is observed that the Co–Mo–Se possesses a low charge transfer resistance owing to the intrinsic metallicity. As a result, the Co–Mo–Se electrode exhibits favorable energy storage properties, including high capacity (221.7 mAh g−1), good rate property, and outstanding stability (95% after 8000 cycles). More importantly, the assembled Co–Mo–Se//active carbon (AC) achieves high energy density (44.7 Wh kg−1) and remarkable durability. Notably, two hybrid devices connected in series successfully power an electronic watch for 70 min, demonstrating its practical applicability. These results indicate that the synthesized hollow Co–Mo–Se nanosheet arrays have promising applications as electrode materials for high-performance energy storage devices. • Co-MOF was employed as template to obtain hollow Co–Mo–Se nanosheet arrays. • The Co–Mo–Se delivers a specific capacity of 221.7 mAh g−1 at 1 A g−1. • The ion exchange/etching method was applied in this work. • The asymmetric supercapacitor delivers high energy and power densities. [ABSTRACT FROM AUTHOR]

NiS 2 is a promising anode material for sodium-ion batteries (SIBs) and capacitors (SICs). However, the sluggish Na+ diffusion and large volume change of bulk NiS 2 during sodiation/de-sodiation lead to poor rate capability and fast capacity decay, limiting its practical application. Herein, we design and prepare well-oriented NiS 2 nanosheets on porous carbon microtubes (denoted as NiS 2 /pCMT) as a novel anode material for SIBs/SHCs. The unique porous hollow carbon tubes and NiS 2 nanosheets can well relieve the repeated stress/strain and maintain the structural integrity of the composite anode during long-term charging/discharging. As a confirmation, a modelled SHC is constructed by using the NiS 2 /pCMT composite as anode and coupling with an activated carbon cathode, delivering a high energy density of 136 Wh kg−1 and good cycling stability. The first-principles density functional theory (DFT) calculations confirm that the NiS 2 nanosheets surface has a high chemical affinity towards Na+ ions, promising the concentration of Na+ ion on/nearby the surface for fast redox reactions during sodiation/de-sodiation of NiS 2. This work provides some new insights for the design and fabrication novel composite electrode materials for applications in beyond lithium-ion batteries/capacitors. • The carbon microtubes have unique tubular structure and good conductivity. • NiS 2 nanosheets uniformly grow on both sides of the carbon microtubes. • The layered NiS 2 nanosheets facilitate the intercalation of the Na+ ions. • The sodium-ion hybrid capacitor delivers high energy and power densities. [ABSTRACT FROM AUTHOR]