Phase Engineering Facilitates\nO–O Coupling\nvia Lattice Oxygen Mechanism for Enhanced Oxygen Evolution on Nickel–Iron\nPhosphide

Nickel–iron-based catalysts are recognized for\ntheir high\nefficiency in the oxygen evolution reaction (OER) under alkaline conditions,\nyet the underlying mechanisms that drive their superior performance\nremain unclear. Herein, we revealed the molecular OER mechanism and\nthe structure-intermediate-performance relationship of OER on a phosphorus-doped\nnickel–iron nanocatalyst (NiFeP). NiFeP exhibited exceptional\nactivity and stability with an overpotential of only 210 mV at 10\nmA cm<sup>–2</sup> in 1 M KOH and a cell voltage of 1.68 V\nat 1 A cm<sup>–2</sup> in anion exchange membrane water electrolyzers.\nThe evolution of active sites and intermediates during OER on NiFeP\nwas in situ probed and correlated using shell-isolated nanoparticle-enhanced\nRaman spectroscopy, complemented by differential electrochemical mass\nspectrometry and density functional theory. These results provide\ndirect evidence that OER proceeds via the lattice oxygen-mediated\nmechanism. Remarkably, phosphorus doping plays a critical role in\nstabilizing the active β-Ni(Fe)OOH phase, which facilitates\nthe *OH deprotonation and the subsequent O–O coupling to form\n*OO intermediates. Our findings offer a deeper understanding of the\nOER mechanism, providing a clear pathway for designing next-generation\nOER catalysts with improved efficiency and durability.