Do the Lattice Oxygen and Oxide Path Mechanisms Operate in the Oxygen Evolution Reaction under Working Conditions?

The mechanistic origin of oxygen evolution reaction (OER) activity remains under debate. The lattice oxygen mechanism (LOM) and oxide path mechanism (OPM) have been widely invoked to rationalize OER activities that appear to surpass the scaling-relation limit of the conventional adsorbate evolution mechanism (AEM). Here, using coverage-resolved density functional theory calculations, we reassess OER pathways on two prototypical catalysts, LaCuO 3 and Ru-doped α-MnO 2 . Surface Pourbaix analysis reveals stable surface terminations under operating conditions that differ markedly from those assumed in previous studies. By resolving each elementary step on these working surfaces, we find that neither the LOM nor the OPM is thermodynamically more favorable than the AEM. Both non-AEM pathways further contain potential-independent chemical steps that impose intrinsic thermodynamic bottlenecks, inconsistent with the experimentally observed increase in OER activity with applied potential. These results highlight the need to establish the operando surface state and evaluate the full elementary-step pathway before assigning OER mechanisms.