Electrocatalytic Water Oxidation at Neutral pH–Deciphering the Rate Constraints for an Amorphous Cobalt‐Phosphate Catalyst System

The oxygen evolution reaction (OER) is pivotal in sustainable fuel production. Neutral-pH OER reduces operational risks and enables direct coupling to electrochemical CO2 reduction, but typically hampered by low current densities. Here, the rate limitations neutral-pH are clarified. Using cobalt-based catalyst films phosphate ions as essential electrolyte bases, current–potential curves recorded simulated. Operando X-ray spectroscopy shows potential-dependent structural changes independent of concentration. Raman uncovers acidification at a micrometer distance from surface, limiting Tafel slope regime proton transport facilitated diffusion either (base pathway) or H3O+ (water pathway). water pathway not associated with an absolute limit energetically inefficient due Tafel-slope increase 60 mV dec−1, shown uncomplicated mathematical model. base specific requirement can support high densities, only accelerated buffer-base diffusion. Catalyst internal other mechanisms do A proof-of-principle experiment that densities exceeding 1 cm−2 also be achieved OER.