Crystal Facet Regulation and Ru Incorporation of Co3O4 for Acidic Oxygen Evolution Reaction Electrocatalysis

Acidic oxygen evolution reaction (OER) has long been the bottleneck of proton exchange membrane water electrolysis. Ru- and Ir-based oxides are currently state-of-the-art electrocatalysts for acidic OER, but their high cost limits their widespread application. Co₃O₄ is a promising alternative, yet the performance requires further improvement. Crystal facet engineering can effectively regulate the kinetics of surface electrochemistry and thus enhance the OER performance. However, the facet-dependent OER activity and corrosion behavior of Co₃O₄ have not been thoroughly studied. In this study, we systematically investigated the OER performance and crystal facet dependency of Co₃O₄. The results demonstrate that Co₃O₄ with mixed {111} and {110} facets exhibits better OER activity and stability than Co₃O₄ with {111} or {100} facets. The surface Co³⁺ species are responsible for the high OER activity, but its transformation to CoO₂ is also the root cause of the dissolution, leading to an activity–stability trade-off effect. The possible approach to addressing this issue would be to increase the Co³⁺ contents by nanostructure engineering. To further improve the performance, Ru is introduced to the best-performing Co₃O₄. The resulting Co₃O₄/RuO₂ heterostructure exhibits an overpotential of 257 mV at 10 mA cm^–2 and can stably catalyze the OER for 100 h.