Mitigation of H2 crossover in PEM water electrolyzers via cathode catalyst layer engineering: Effects of pore former type, loading, and operating pressure

H 2 crossover through the membrane is a critical safety and efficiency concern in proton exchange membrane water electrolyzers (PEMWEs), particularly under pressurized operation. This study develops a cathode catalyst layer (CL) pore-engineering strategy using PEG as a pore-forming agent to regulate gas transport within the CL. The molecular weight of PEG governs its dispersion behavior in the catalyst ink and the architecture of the resulting pore network. An intermediate molecular weight additive generates a uniform and interconnected pore framework that facilitates rapid H 2 removal from the cathode CL. As a result, H 2 permeation through the membrane is suppressed while maintaining comparable electrochemical kinetics. Optimization of PEG loading identifies 60 wt% as the optimal condition, delivering reduced H 2 crossover, improved high-current-density performance, and enhanced durability. The engineered CL also maintains lower crossover levels under pressurized operation, highlighting pore-structure control as a strategy for improving the safety and stability of PEMWEs.