Role of Potassium in Electrocatalytic Water Oxidation Investigated in a Volume‐Active Cobalt Material at Neutral pH

The oxygen evolution reaction (OER) is crucial in systems for sustainable production of hydrogen and other fuels. Catalytic OER materials often undergo potential-induced redox transitions localized at metal sites. For volume-active catalyst-materials, these are necessarily coupled to charge-compensating relocation ions entering or leaving the material, which insufficiently understood. binding mode mechanistic role redox-inert a cobalt-based oxyhydroxide material (CoCat) when operated neutral pH potassium-phosphate (KPi) electrolyte investigated by i) determination K:Co P:Co stoichiometries various KPi-concentrations electrode potentials, ii) operando X-ray spectroscopy potassium cobalt K-edges, iii) novel time-resolved experiments facilitating comparison K-release Co-oxidation kinetics. Potassium likely binds non-specifically within water layers interfacing Co-oxyhydoxide fragments involving potassium–phosphate ion pairs. potassium-release kinetics potential-independent with fast-phase time-constant about 5 s thus clearly slower than Co oxidation 300 ms. It concluded that flow realized neither nor phosphate ions, but protons. results reported here relevant also broader class catalyst amorphized near-surface regions microcrystalline materials.