Nanosurface-induced construction of NiCoP–CoP heterostructure nanobristle electrodes for highly efficient alkaline hydrogen evolution reaction

Abstract

Developing highly efficient hydrogen evolution reaction (HER) catalysts is substantially important for high-performance water electrolyzers for “green hydrogen” production. Transition metal phosphides are promising HER catalyst candidates because of their intrinsically excellent conductivity and acid/alkali stability. In order to enhance their HER activity, one approach is to increase the density of active sites on the electrode surface through the design of the catalyst's micro- or nano-structures. However, the in situ formed catalysts on a nano-sized substrate are accompanied by the “nano-effect” of the substrate that may influence their phase/composition, thereby altering the catalytic activity, which has rarely been studied. In this work, we revealed that the phase composition of the Ni_xCoP–CoP nanobristles can be modulated by controlling the solid-state nickel element diffusion from the nickel nanowire arrays (NNA). Density Functional Theory (DFT) calculation confirmed that the obtained NiCoP–CoP heterostructure has a lower energy barrier for water dissociation than NiCoP and CoP. The NiCoP–CoP@NNA electrode delivers an ultra-low overpotential of 20 mV at 10 mA cm⁻² with a Tafel slope of 28 mV dec⁻¹, and is one of the best alkaline HER phosphide catalysts reported so far. This discovery broadens the knowledge of materials synthesis and provides insights into regulating the phase and composition of materials.