Recent progress of manganese dioxide based electrocatalysts for the oxygen evolution reaction

The oxygen evolution reaction (OER) represents an anodic reaction for a variety of sustainable energy conversion and storage technologies, such as hydrogen production, CO₂ reduction, etc. To realize the large-scale implementation of these technologies, the sluggish kinetics of the OER resulting from multi-step proton/electron transfer and occurring at the gas–liquid–solid triple-phase boundary needs to be accelerated. Manganese oxide-based (MnO_x) materials, especially MnO₂, have become promising non-precious metal electrocatalysts for the OER under acidic conditions due to the good trade-off between catalytic activity and stability. This paper reviews the recent progress of MnO₂-based materials to catalyze the OER through either the traditional adsorbent formation mechanism (AEM) or the emerging lattice-oxygen-mediated mechanism (LOM). Pure manganese dioxide OER catalysts with different crystalline structures and morphologies are summarized, while MnO₂-based composite structures are also discussed, and the application of MnO₂-based catalysts in PEMWEs is summarized. Critical challenges and future research directions are presented to hopefully help future research.