Unraveling Structure-Performance Trade-Offs in Porous Transport Layers for PEM Water Electrolysis.

Scalable hydrogen production using proton exchange membrane water electrolyzers (PEMWEs) depends on overcoming efficiency losses arising from coupled multiphase, multicomponent transport, and interfacial phenomena across the membrane electrode assembly. Here, we demonstrate a multiscale computational framework that combines pore network modeling with finite-element-based reactive transport simulations to accurately and efficiently resolve structure-performance trade-offs in porous transport layers (PTLs). We perform experiments for both commercial single-layer PTLs and microporous layer (MPL)-integrated configurations to benchmark the electrochemical model, achieving excellent agreement between modeling and measurements. We show that in single-layer PTLs, open porous networks facilitate mass transport but incur large voltage penalties from the PTL-anode catalyst layer (ACL) contact resistance. Bilayer architectures with thin and moderately dense MPLs reduce these losses by simultaneously improving transport and contact. Finally, in stratified multilayer stacks, combining fine pores near the ACL with highly porous backing layers delivers an enhanced performance at high current densities. Altogether, these results establish mechanistic guidelines for porosity-informed PTL design that minimize interfacial resistance and enable high-efficiency PEMWE operation.