Crystal phase engineering and surface reconstruction in Co–Mn phosphides: unraveling the mechanisms of high-performance water oxidation catalysis

Abstract

Crystalline and amorphous catalysts offer disparate advantages in reducing the overpotential of the oxygen evolution reaction (OER). Crystalline phases provide excellent electrical conductivity, while amorphous phases offer abundant unsaturated active sites. This study explores a synergistic strategy that integrates these benefits to develop high-performance OER catalysts with enhanced activity and stability. By employing controlled annealing followed by phosphating, we engineered a transition from low-crystallinity MnP–Co₃P/NF to high-crystallinity MnP–Co₃(PO₄)₂/NF, effectively tuning the balance between conductivity and active site availability. Advanced spectroscopic characterization studies (including X-ray photoelectron spectroscopy (XPS), zeta potential analysis, ultraviolet photoelectron spectroscopy (UPS) and electrochemical measurements) reveal that the high-crystallinity MnP–Co₃(PO₄)₂/NF catalyst exhibits superior hydrophilicity, an enriched concentration of phosphorus vacancies, and enhanced charge redistribution, collectively leading to significantly improved OER kinetics. The catalyst achieved low overpotentials of 281 mV at 50 mA cm⁻² and 306 mV at 100 mA cm⁻², with exceptional stability for 230 h at 100 mA cm⁻², outperforming comparable systems and commercial noble metal catalysts. In situ studies revealed faster formation of the active CoOOH phase on high-crystallinity MnP–Co₃(PO₄)₂/NF. This work provides valuable insights into designing efficient and durable OER catalysts for energy conversion applications.