Guarding active sites and electron transfer engineering of core-shell nanosheet as robust bifunctional applications for overall water splitting and capacitors

It is urgent to design low-cost and high-performance multifunctional materials for energy storage and conversion system due to the depletion of energy resources and environmental pollution. Here, we construct three-dimensional (3D) core-shell structure (NiCo₂O₄@NiS) with good energy storage and conversion performance towards electrocatalytic water splitting and capacitors. Experimental results demonstrate that the excellent electrochemical performance are attributed to the hierarchical structure in favor of substance diffusion, the interaction effect which enhances abundant active sites, and direct growing on Ni foam conductive to electron transfer. As for overall water splitting, using the as-prepared materials as the anode and the cathode, the system affords a current density of 10 mA/cm² with a low voltage of 1.65 V along with a robust stability. Furthermore, the hybrid hierarchical electrode exhibits a specific capacitance of 3833 F/g, which is considerably superior to the previous reported results. The capacitor retains above 97.7% of initial capacitance after 3000 cycles, indicating its excellent cycling stability. The present study provides guiding significance for other multifunctional applications in the aspect of energy storage and conversion.