Crystal Facet Regulation and Ru Incorporation of CoO 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. CoO 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 CoO have not been thoroughly studied. In this study, we systematically investigated the OER performance and crystal facet dependency of CoO. The results demonstrate that CoO with mixed {111} and {110} facets exhibits better OER activity and stability than CoO with {111} or {100} facets. The surface Co species are responsible for the high OER activity, but its transformation to CoO 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 Co contents by nanostructure engineering. To further improve the performance, Ru is introduced to the best-performing CoO. The resulting CoO/RuO heterostructure exhibits an overpotential of 257 mV at 10 mA cm and can stably catalyze the OER for 100 h.