Influence of dynamic operating cycles on the performance and degradation of PEM electrolyzers: a combined electrical, electrochemical, and morphological analysis

Proton exchange membrane water electrolysis (PEMWE) is a key technology for renewable hydrogen production, but large-scale implementation remains limited by durability issues under real operating conditions. This work presents a systematic evaluation of three representative dynamic operating modes: On/Off, On/Standby and Continuous. The assessment combines electrical, electrochemical and morphological characterization of the membrane, cathode and anode. After 365 cycles, differentiated degradation pathways were observed. The On/Standby mode exhibited the most severe deterioration, with a total resistance of TR = 8300.9 mΩ, sulfur-enriched zones in the membrane and a compacted anodic surface with particle coalescence and partial collapse of the porous structure. The Continuous mode showed intermediate degradation, with TR = 2310.0 mΩ, sulfur-enriched membrane regions and partial densification of the anodic catalyst layer. In contrast, the On/Off mode largely preserved electrochemical and structural integrity, recording the lowest resistance increase (TR = 1902.6 mΩ) and no significant morphological changes in the components. Consistent with these trends, the additional input power required to sustain the same current density increases sharply in the On/Standby mode, whereas the On/Off and Continuous modes require much smaller increases than in the On/Standby mode, although still higher than in the reference cell, reflecting different degrees of resistive degradation. These findings confirm that degradation in PEM electrolyzers is mainly governed by anode and membrane processes, with comparatively resilient cathodes. Joint analysis of impedance-derived resistances, input power and post-mortem microstructure establishes a degradation hierarchy (On/Standby > Continuous > On/Off) that guides selection of operating strategies balancing performance and durability.