Experimental and Theoretical Insights into Transition-Metal (Mo, Fe) Codoping in a Bifunctional Nickel Phosphide Microsphere Catalyst for Enhanced Overall Water Splitting

The facile synthesis of efficient non-precious-metal-based bifunctional catalysts for overall water splitting is highly desirable from both industrial and environmental perspectives. This study reports the electrodeposition and characterization of a transition-metal (Mo, Fe)-codoped nickel phosphide (Ni3P:FeMo) bifunctional catalyst for enhanced overall water splitting in an alkaline medium. The Ni3P:FeMo catalyst exhibited outstanding electrocatalytic performance for both the hydrogen evolution reaction and oxygen evolution reaction with low overpotentials of -103 and 290 mV, respectively, at a high current density of 100 mA/cm2 along with fast electrocatalytic kinetics. A full water-splitting electrolyzer consisting of a bifunctional Ni3P:FeMo catalyst required a low cell voltage of 1.48 V to attain a current density of 10 mA/cm2 with excellent stability for more than 50 h. Density functional theory calculations provided insights into the microscopic mechanism of the effective modulation of the p- and d-band centers of the P and Ni active sites by the Mo and Fe codoping of Ni3P, thereby enhancing the bifunctional catalytic activity of Ni3P.