Superhydrophilic/Superaerophobic Hierarchical NiP2@MoO2/Co(Ni)MoO4 Core–Shell Array Electrocatalysts for Efficient Hydrogen Production at Large Current Densities

Rationally constructing low-cost, high-efficiency, and durable electrocatalysts toward the hydrogen evolution reaction at large current densities is imperative for water splitting, especially for large-scale industrial applications. Herein, a hierarchical core-shell NiP₂@MoO₂/Co(Ni)MoO₄ cuboid array electrode with superhydrophilic/superaerophobic properties is successfully fabricated and the formation mechanism of the core-shell structure is systematically investigated. Through an in situ partially converted gas-solid reaction during the phosphating process, Ni and Co elements are leached and rearranged to form NiP₂ particles and amorphous CoO as the shell layer and the inner undecomposed Co(Ni)MoO₄ crystals serve as the core layer. Because of its seamless core-shell structure and superhydrophilicity/superaerophobicity of hierarchical cuboid arrays, NiP₂@MoO₂/Co(Ni)MoO₄ exhibits superior HER activity in 1 M KOH with only an overpotential of 297 mV to deliver 1000 mA cm^-2 and can work steadily for 650 h at 200 mA cm^-2. Remarkably, when coupled with NiFe LDH for overall water splitting, it can drive an AA battery with an ultralow cell voltage of 1.49 V to deliver 10 mA cm^-2. This work sheds new light on designing large-current-density efficient HER electrocatalysts for large-scale industrial applications.