Recent progress of advanced manganese oxide-based materials for acidic oxygen evolution reaction: Fundamentals, performance optimization, and prospects

The oxygen evolution reaction (OER) is the basis of various sustainable energy conversion and storage techniques, especially hydrogen production by water electrolysis. To realize the practical application of hydrogen energy and mass-scale hydrogen production via water electrolysis, several obstacles, such as the multi-electron transfer OER process with sluggish kinetics and overall high reaction barrier, should be overcome. Manganese oxide-based (MnOx) materials, especially MnO2, have emerged as promising non-noble electrocatalysts for water electro-oxidation under acidic conditions due to their well-balanced properties between catalytic activity and stability. This review introduces the fundamental understanding of the catalytic OER process on MnOx-based materials, including the conventional adsorbate evolution mechanism (AEM) and emerging lattice oxygen oxidation mechanism (LOM). The rational screening and prediction of MnOx-based catalysts that can stably catalyze OER in acid are summarized based on Pourbaix diagram analysis and thermodynamic density functional theory (DFT) calculations. Then, the up-to-date progress of upgrading the OER catalytic performance of MnOx-based catalysts by composite construction is reviewed. Afterward, feasible strategies to improve the electrocatalytic activity and lifetime of MnOx-based catalysts are systemically discussed in terms of crystal structure control, reasonable setting of working potential and electrolyte environment, optimal selection of acid-stable conductive supports, and self-healing engineering. Finally, future scientific challenges and research directions are outlined to guide the construction of advanced MnOx-based electrocatalysts for OER in acid.