Gradient Engineered Microporous Layers for Enhanced Oxygen Transport in PEM Water Electrolysis

Abstract Microporous layers (MPLs) improve catalyst utilization in proton exchange membrane water electrolysis (PEMWE), but must accommodate rapid oxygen removal at high current densities. Dense or poorly oriented MPLs can convert an interfacial benefit into a gas-transport penalty. Here, we introduce a gradient engineered MPL (G-MPL) where porosity and pore size increase from the catalyst side toward the porous transport layer (PTL). This architecture reduces voltage to 2.161 V at 5 A cm–2, outperforming uniform and reverse-gradient MPLs. Electrochemical analysis indicates the gain arises from reduced ohmic and transport-related losses, rather than from interfacial contact alone. Digital twin analyses show the pore gradient promotes oxygen evacuation and limits gas-filled regions restricting water access. Under limited water supply, the G-MPL retains stable operation at high current density. These results establish directional pore grading as an MPL design strategy for maintaining catalyst layer/PTL contact while managing oxygen-water transport in high current density PEMWE.