Engineering Iridium-Based Oxygen Evolution Reaction Electrocatalysts for Proton Exchange Membrane Water Electrolyzers

The electrocatalytic water splitting technology, especiallyprotonexchange membrane water electrolyzers (PEMWEs), is one of the corehydrogen production technologies to achieve carbon-free energy cycling.However, high acid corrosion and anodic potential operating conditionspose serious challenges for the development of PEMWEs. It is urgentto explore highly active, durable, and compatible anodic catalystsfor the complex oxygen evolution reaction (OER). Hitherto, iridium(Ir)-based electrocatalysts (IBCs) with trade-off catalytic activityand stability are the primary candidates for the OER. Yet, the continuedhuge consumption of expensive and scarce Ir species severely hindersthe widespread deployment of PEMWEs. It is necessary to systematicallyunderstand the latest research progress in IBCs to guide the controllableconstruction of catalysts with low-Ir loading to meet industrial demands.In this review, the conventional OER catalytic mechanism and Ir species-relatedfailure modes are introduced. Subsequently, four common classes ofIBCs, including Ir-based metals, oxides, perovskites, and pyrochlores,as well as attempts to correlate structural features of catalystswith their performance are reviewed. Within this scenario, the actualperformances of bright representative IBCs applied in practical PEMWEsare also discussed. At the end of this review, unresolved issues andchallenges in the field are proposed with a view to formulating effectivestrategies to break the bottleneck of commercial deployment of PEMWEs.