NiSe@Ni_1−xFe_xSe₂ Core–Shell Nanostructures as a Bifunctional Water Splitting Electrocatalyst in Alkaline Media

Herein a facile synthesis methodology is reported that results in a unique 3D NiSe@Ni_1−xFe_xSe₂ core–shell nanostructure on nickel foam substrate, where Ni_1−xFe_xSe₂ nanosheets are fabricated on NiSe nanowires through an iron-doping-induced phase transformation process under solvothermal conditions. This material demonstrates stable hydrogen and oxygen evolution activity in 1.0 m KOH with a small overpotential of 153 mV@−10 mA cm⁻² and 236 mV@100 mA cm⁻², respectively. Furthermore, an efficient and stable water electrolyzer with NiSe@Ni_1−xFe_xSe₂/nickel foam as both anode and cathode is fabricated, which requires a low overpotential of 1.60 V to deliver a current density of 10 mA cm⁻². Such ion-doping-induced phase transformation paves a new way for fabricating highly efficient electrocatalysts for energy storage and conversion.