Stabilizing Cobalt in the Delafossite Lattice for the Acidic Oxygen Evolution Reaction

We investigate how lattice structure influences cobalt oxide stability under acidic oxygen evolution reaction (OER) conditions by comparing Co3O4 spinel and HCoO2 delafossite catalysts. Although Co3O4 exhibits an earlier OER onset, it undergoes rapid activity loss during cyclic voltammetry in 0.1 M HClO4. Inductively coupled plasma mass spectrometry dissolution analysis reveals that HCoO2 dissolves significantly less than Co3O4 under galvanostatic and potentiodynamic operation, despite similar open-circuit dissolution, indicating that its enhanced stability emerges under high oxidizing potentials. O 1s XPS further shows that Co3O4 experiences irreversible redistribution of surface oxygen species after aging, whereas HCoO2 largely retains its initial surface chemistry. When implemented in a proton exchange membrane water electrolyzer, HCoO2 also demonstrates improved performance retention and avoids the pronounced voltage losses observed for Co3O4 following extended operation. Across both materials, increases in the Co2+/3+ oxidation potential correlate with declining OER activity, suggesting a link between deactivation and progressive surface electronic evolution. These results suggest that the delafossite lattice stabilizes cobalt more effectively during acidic OER and could provide a structural platform for further catalyst design.