Experimental and simulation study of H₂ crossover in PEM water electrolysis for high-pressure hydrogen production up to 20 MPa

High-pressure proton exchange membrane (PEM) water electrolysis offers considerable advantages, particularly in enabling direct integration with hydrogen storage and transportation systems while eliminating the need for external mechanical compressors. However, H₂ crossover is a bottleneck that induces high H₂-in-O₂ content and low overall efficiency during high-pressure PEM water electrolysis. This study investigates H₂ crossover in PEM water electrolysis by combining in situ measurements and numerical simulations over a differential pressure range of 0–20 MPa. A linear correlation was observed between hydrogen crossover and current density within the range of 0–1 A cm⁻². The cathodic hydrogen mass transfer coefficient was determined to range from 1.6 to 3.2 mm s⁻¹, and the hydrogen solubility was estimated as 1.1 × 10⁻³ mmol m⁻³ Pa⁻¹. The results highlight the importance of optimizing mass transfer and reducing hydrogen solubility within the cathode catalyst layer to mitigate H₂ crossover during high-pressure PEM water electrolysis.