Cobalt oxide-based catalysts for acidic oxygen evolution reactions

Proton exchange membrane water electrolysis (PEMWE) is a cornerstone technology for green hydrogen production, yet the sluggish oxygen evolution reaction (OER) in acidic media remains a major bottleneck. Noble metal oxides such as IrO2 and RuO2 are effective but suffer from high cost and scarcity. As a non-precious alternative, spinel cobalt oxide (Co3O4) has attracted attention due to its promising performance results from its mixed-valence structure, tunable electronic properties and catalytic potential. However, its practical application is challenged by poor conductivity, moderate activity and instability under acidic conditions due to proton attack and lattice degradation. This review summarises recent advances in Co3O4-based electrocatalysts for acidic OER. We first introduce three key OER pathways: adsorbate evolution mechanism (AEM), lattice oxygen mechanism (LOM) and oxide path mechanism (OPM) and their relevance to Co3O4 performance. Then, we introduce the structural and electronic characteristics of Co3O4 that influence its catalytic behaviour. Next, we review a range of engineering strategies, including element doping, heterostructure construction, surface modification and defect engineering, all aimed at enhancing the activity and durability of Co3O4. Finally, we highlight critical challenges and offer perspectives for advancing Co3O4 as a viable acidic OER catalyst.