Performance and durability trade-offs in low-iridium catalyst layers for PEM water electrolysis

To deploy proton-exchange membrane (PEM) water electrolyzers at a gigawatt scale, the iridium-specific power density must be reduced to below 0.1 mg Ir W −1 . Significant variability in reported performance and durability benchmarks makes it difficult to define clear pathways for technological improvement. Here, we report a device-level investigation combining multimodal diagnostics with long-term durability testing across four commercial catalysts at loadings from 0.1 to 0.8 mg Ir cm −2 . While all catalysts achieve the 0.1 mg Ir W −2 target, this cannot be met at lower heating value-based efficiencies above 75% through catalyst design alone. Durability testing over 500 and 1,000 h shows that degradation rates decrease with extended operation and that each catalyst exhibits distinct, loading-dependent behavior. Postmortem characterization confirms progressive catalyst crystallization as a primary contributor to kinetic degradation. These findings demonstrate that future deployment targets depend far more on reducing cell resistance and ensuring long-term durability than on advancing intrinsic catalyst activity.