Operando Visualization of Cathode Water Management in Proton Exchange Membrane Water Electrolyzers Using Synchrotron X-Ray Radiography.

Optimizing water management in proton exchange membrane water electrolyzers (PEMWEs) is essential for reducing the levelized cost of hydrogen and ensuring safe operation, as it influences both water vapor carryover and hydrogen crossover. In this study, we establish an operando synchrotron X-ray radiography system to visualize the liquid water distribution and dynamics within the cathode gas diffusion layer. Quantitative analysis of the time-resolved radiographic data reveals that the cathode water behavior is primarily governed by current density through its effect on electro-osmotic water supply and hydrogen-gas-driven water removal, together with cell temperature through liquid-vapor phase transitions. At lower temperatures, liquid water preferentially accumulates beneath the flow-field ribs due to localized current density and limited evaporative drying. Increasing temperature enhances evaporation, suppresses liquid water accumulation, and shifts the dominant transport mode from continuous to pulsating water transport. The results indicate that evaporation-condensation processes play a critical role in regulating cathode water dynamics. These findings provide mechanistic insight into cathode water management and its implications for water vapor carryover and hydrogen crossover in PEMWE systems.