Structural Insights into Proton Exchange Membrane Water Electrolyzers after Long-Term Operation Using Advanced 3D Focused Ion Beam–Scanning Electron Microscopy Tomography

Abstract Proton exchange membrane water electrolyzers (PEMWEs) are key to sustainable hydrogen production, but their long-term performance is limited by degradation, particularly in the membrane electrode assembly (MEA), which remains a barrier to commercial viability. Moreover, the need for corrosion-resistant materials and the intricate fabrication of bipolar plates and porous transport layers (PTLs) further impede large-scale deployment and account for a major share of the stack cost. Because lifetime and replacement costs are strongly influenced by the local microstructure and contact conditions, especially at the anode/PTL interface, a multiscale characterization approach combining 3D focused ion beam–scanning electron microscopy (FIB–SEM) with time-of-flight mass spectrometry is used to investigate degradation in an MEA after several thousand hours of operation under industrially relevant conditions. The 3D reconstruction and ppm-level chemical mapping show that local contact heterogeneities at welds in an expanded-metal mesh PTL act as degradation hotspots. At these sites, intensified catalyst utilization accelerates iridium dissolution, driving iridium migration and deposition as extended filaments into the membrane. Concurrently, membrane voids are formed beneath these sites, accompanied by iron contamination detected at both contact types. In contrast, general contact regions mainly show a thin redeposition layer without voids or filaments. These findings provide a mechanistic framework that links local contact conditions and microstructural heterogeneities to coupled catalyst and membrane degradation, supporting design rules for improved PEMWE durability.