Operando Visualisation of Cathode Water Management in Proton Exchange Membrane Water Electrolysers Using Synchrotron X-ray Radiography

Optimising water management in proton exchange membrane water electrolysers (PEMWEs) is essential for reducing the levelised cost of hydrogen and ensuring safe operation, as it influences both water vapour carryover and hydrogen crossover. In this study, we established an operando synchrotron X-ray radiography system to visualise the liquid water distribution and dynamics within the cathode gas diffusion layer. Quantitative analysis of the time-resolved radiographic data revealed that the cathode water behaviour 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-vapour phase transitions. At lower temperatures, liquid water preferentially accumulates beneath the flow-field ribs owing to localised current density and limited evaporative drying. Increasing temperature enhanced evaporation, suppressed liquid water accumulation, and shifted 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 vapour carryover and hydrogen crossover in PEMWE systems.