Design of PEM water electrolysers with low iridium loading

To enable gigawatt-scale deployment of proton exchange membrane water electrolysers (PEMWEs), drastic reductions from current iridium loadings of 2–3 mg Ir cm −2 to less than 0.4 mg Ir cm −2 must occur due to iridium's high cost and scarcity. State-of-the-art systems use these high loadings to compensate for degradation experienced over prolonged operation. Thus, to attain low loadings while meeting commercial lifetime targets, factors such as ink formulation, MEA fabrication, catalyst layer–porous transport layer (CL–PTL) contact, and catalyst durability must be optimised. This review paper discusses the fundamentals of PEMWE technology and the modifications/improvements necessary for effective low iridium-loading design. Important milestones for future research include developing durable catalyst layers at low loadings, optimising the CL–PTL interface, and improving roll-to-roll production processes.