NiO@CoSe nanostructures for high-performance asymmetric supercapacitors and efficient electrocatalysts.

It is very important to design bi-functional materials for sustainable energy storage and conversion. NiO electrodes are promising candidates for supercapacitors and electrocatalysts, but the poor cycling stability limits their practical applications. To solve this issue, we prepared core-shell structured NiO@CoSe samples by a multi-step hydrothermal protocol. They exhibit a specific capacitance of 1130 C g at a current density of 1 A g. An asymmetric device was assembled using the obtained product as the cathode. It delivers an energy density of 103.8 W h kg at 2700 W kg. As an electrocatalyst for hydrogen evolution reactions, the NiO@CoSe sample presents an overpotential of 82.8 mV@10 mA cm and a Tafel slope of 72.14 mV dec, respectively.