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

The electrocatalytic water splitting technology, especially proton exchange membrane water electrolyzers (PEMWEs), is one of the core hydrogen production technologies to achieve carbon-free energy cycling. However, high acid corrosion and anodic potential operating conditions pose serious challenges for the development of PEMWEs. It is urgent to explore highly active, durable, and compatible anodic catalysts for the complex oxygen evolution reaction (OER). Hitherto, iridium (Ir)-based electrocatalysts (IBCs) with trade-off catalytic activity and stability are the primary candidates for the OER. Yet, the continued huge consumption of expensive and scarce Ir species severely hinders the widespread deployment of PEMWEs. It is necessary to systematically understand the latest research progress in IBCs to guide the controllable construction of catalysts with low-Ir loading to meet industrial demands. In this review, the conventional OER catalytic mechanism and Ir species-related failure modes are introduced. Subsequently, four common classes of IBCs, including Ir-based metals, oxides, perovskites, and pyrochlores, as well as attempts to correlate structural features of catalysts with their performance are reviewed. Within this scenario, the actual performances of bright representative IBCs applied in practical PEMWEs are also discussed. At the end of this review, unresolved issues and challenges in the field are proposed with a view to formulating effective strategies to break the bottleneck of commercial deployment of PEMWEs.