Mn-doped NiCoP Nanopin Arrays as High-Performance Bifunctional Electrocatalysts for Sustainable Hydrogen Production via Overall Water Splitting

Active bifunctional electrocatalysts that can catalyze both hydrogen evolution reaction (HER) and oxygen evolution reaction (OER) are highly desirable for overall water splitting. One such catalyst, NiCoP, demonstrates potential due to its unique electronic and structural properties that allow for efficient charge transfer between the catalyst and reactants. However, its OER performance is often unsatisfactory compared to its high HER performance. To address this problem, we prepared Mn-doped nickel cobalt phosphide (Mn-NiCoP) with nanopins arrays by in situ growth on nickel foam (NF), which only requires the overpotentials of 148 mV for HER and 266 mV for OER at a high current density of 100 mA cm−2. Consequently, the achieved water splitting performance with Mn-NiCoP as both anode and cathode at a high current density of 100 mA cm−2 were as low as 1.69 V, and its maintenance was 94% after 240 hours. Furthermore, we demonstrate that the simultaneous improvement of both the OER and HER performances on Mn-NiCoP is due to the synergistic effect of the preferred moderate amount of Mn doping and Co alloying, through first-principles calculations of electronic structures, electrochemical stabilities, and reaction chemical potentials for different surface adsorption states. Overall, this work provides inspiration for optimizing the OER performance of traditional HER catalysts, thereby promoting overall water splitting using only one catalyst in the same solution.