Designing and Engineering Efficient and Durable Low-Ir Catalysts at Multiple Scales for Water Electrolysis: Atomic Structures, Nanoscale Morphologies, and Macroscopic Electrode Configurations

Proton exchange membrane water electrolyzers (PEMWEs) stand out as a promising technology for green hydrogen production due to their numerous advantages over other water electrolysis technologies, including high efficiencies, reliability, rapid dynamic response, and the feasibility of operating at high pressures. Unfortunately, only extremely scarce and expensive Ir-based anode catalysts are viable for PEMWEs due to their intrinsic catalytic activity and stability under challenging oxidative potentials and acidic environments. Currently, a high Ir loading (2 mg cm⁻²) in the membrane electrode assembly (MEA) is required to achieve reasonable performance and durability. Practical applications of PEMWEs at the gigawatt scale urgently require efficient ultra-low Ir catalysts (less than 0.1 mg cm⁻²) in the anode with adequate performance and long-term durability through exploring innovative and effective strategies for catalyst design and engineering at multiple scales. This review aims to provide a comprehensive understanding and perspective on the development of advanced ultra-low Ir-based electrocatalysts in terms of their intrinsic activity and stability associated with the atomic structures, Ir utilization and mass/charge transports at the nanoscale, and favorable interfaces with other critical components at the macroscale configuration, such as porous transport layers and membranes, in MEAs.