Medium entropy phosphide promotes reaction kinetics for efficient and stable water oxidation at large-current-density

Developing noble-metal-free oxygen evolution reaction (OER) electrocatalysts with stable performance at large working current is an imperative and yet formidable challenge for practical large scale water splitting. In this study, by inheriting hierarchical nanostructure and elemental homogeneity of Prussian blue analogues, a series of medium entropy transition metal phosphides (METMP) OER catalysts with high cost-effectivity, efficiency and stability were precisely prepared. Specifically, the METMP-based ((FeCoNi)P/Ni₂P-NF) catalyst demonstrates exceptional performance with an overpotential of only 232 mV at 50 mA cm^-2 and a Tafel slope of 52.7 mV dec^-1, significantly superior to its less entropy counterparts and commercial RuO₂. Moreover, it even maintains stability at the industrial standard current density of 500 mA cm^-2 for over 200 hours. Density functional theory (DFT) calculations indicates that the synergistic effect of Fe, Co, Ni modulates electronic structure of METMPs, which effectively reduces the energy barrier for the rate-determining HOO* formation step, thereby considerably enhancing catalytic activity. This work not only contributes to the fundamental understanding of the role of medium/high entropy in catalysis but also paves the way for the development of next-generation electrocatalysts for energy-related applications.