S/V co-doped Ni2P microflowers enable efficient and stable saline water electrolysis through local microenvironment engineering

Abstract

Transition metal phosphides (TMPs) are ideal catalyst alternatives to precious metals for water electrolysis. However, their sluggish reaction kinetics hamper practical widespread application. Herein, an S,V-co-doped Ni₂P electrocatalyst with a microflower-like spherical structure was successfully constructed via a facile elemental co-doping strategy for overall water splitting. Combined experimental characterization studies, in situ electrochemical measurements, and density functional theory (DFT) calculations demonstrate that S and V co-doping can effectively modulate the local microenvironment of Ni active sites, tune the adsorption energy of reaction intermediates, and reduce the energy barrier of the rate-determining step (RDS), thereby endowing the catalyst with outstanding electrocatalytic activity. Specifically, the catalyst exhibits ultra-low overpotentials of only 208 mV (for the OER) and 185 mV (for the HER) at a current density of 100 mA cm⁻², along with a long-term stability of 200 h for both half-reactions. For overall water splitting, a cell voltage of merely 1.42 V is required to achieve 10 mA cm⁻². Furthermore, the in situ formed SO_x⁻ and PO_x⁻ protective layers, derived from the oxidation of surface S and P species, can effectively mitigate Cl⁻ induced corrosion and oxidation. As a result, S,V-Ni₂P/NF exhibits excellent OWS performance in saline electrolyte, requiring a cell potential of only 1.48 V to reach 10 mA cm⁻². This work provides a facile and efficient approach for enhancing the reaction kinetics of transition metal phosphide catalysts via an anion–cation co-doping strategy.