Iridium-based catalysts for oxygen evolution reaction in acidic media: Mechanism, catalytic promotion effects and recent progress

Iridium (Ir)-based catalysts are highly efficient for the anodic oxygen evolution reaction (OER) due to high stability and anti-corrosion ability in the strong acid electrolyte. Recently, intensive attention has been directed to novel, efficient, and low-cost Ir-based catalysts to overcome the challenges of their application in the water electrolysis technique. To make a comprehensive understanding of the recently developed Ir-based catalysts and their catalytic properties, the mechanism and catalytic promotion principles of Ir-based catalysts were discussed for OER in the acid condition aimed for the proton exchange membrane water electrolyzer (PEMWE) in this review. The OER catalytic mechanisms of the adsorbate evolution mechanism and the lattice oxygen mechanism were first presented and discussed for easy understanding of the catalytic mechanism; a brief perspective analysis of promotion principles from the aspects of geometric effect, electronic effect, synergistic effect, defect engineering, support effect was concluded. Then, the latest progress and the practical application of Ir-based catalysts were introduced in detail, which was classified into the varied composition of Ir catalyst in terms of alloys, hetero-element doping, perovskite, pyrochlore, heterostructure, core–shell structure, and supported catalysts. Finally, the problems and challenges faced by the current Ir-based catalyst in the acidic electrolyte were put forward. It is concluded that highly efficient catalysts with low Ir loading should be developed in the future, and attention should be paid to probing the structural and performance correlation, and their application in real PEMWE devices. Hopefully, the current effort can be helpful in the catalysis mechanism understanding of Ir-based catalysts for OER, and instructive to the novel efficient catalysts design and fabrication.