Robust iron-doped nickel phosphides in membrane-electrode assembly for industrial water electrolysis

Water electrolysis, a pivotal process for the production of green hydrogen, is a crucial step toward realizing the hydrogen economy. To advance its industrialization, it is essential to develop a highly efficient and economical catalyst along with a low-resistance electrolyzers. In pursuit of this goal, we synthesize a cost-effective iron-doped nickel phosphide electrocatalyst through a hydrothermal synthesis followed by post-phosphorization process. This catalyst exhibits exceptional performance, with an overpotential at 10 mA cm-2 (η10) of 216 mV for oxygen evolution reaction, the rate-determining step for water electrolysis. It overperforms the that of pristine nickel phosphide (NiPx, η10 = 284 mV). Operando X-ray absorption spectroscopy reveals the robust nature of the iron-doped nickel phosphide catalyst during water electrolysis, in stark contrast to the pristine nickel phosphide, which undergoes oxidation, thereby impacting overall catalytic activity. When integrated into a membrane-electrode assembly (MEA) system, our iron-doped nickel phosphide displays voltages of 1.51 V at 10 mA cm-2 (EE = 81.5%) and 1.66 V at 100 mA cm-2 (EE = 76.4%) without iR-correction. Moreover, it achieves a current density of 345 mA cm-2 at an applied voltage of 2 V without iR-correction, meeting industrial criteria. These findings underscore the superior catalytic activity of the robust phosphide phase for water electrolysis.