Br-induced P-poor defective nickel phosphide for highly efficient overall water splitting

Development of efficient electrocatalysts requires construction of catalytic surfaces with moderate H adsorption energy. Here, we address this challenge by Br-induced formation of P-poor defective nickel phosphide and show that the H adsorption energy can be optimized by regulating the vacancy concentration. We show that when such defective Ni12P5−xBrx nanoparticles are distributed on the surface of Ni2P nanosheets (Ni12P5−xBrx/Ni2P NS), excellent catalytic activity for water splitting is obtained in alkaline media. Density functional theory computations revealed that Br doping induce the formation of a P-poor nickel phosphide with vacancies, leading to an optimal H adsorption strength with a volcano-type relationship. This is the best reported for a non-precious metal phosphide at present: the overpotential for HER is 18 mV at 10 mA cm−2 and 155 mV for OER. This leads to an exceptionally low cell voltage requirement of only 1.44 V to drive overall water splitting in an alkaline electrolyzer.