Interface Engineering of Porous Transport Layer‐Catalyst Layer in Proton Exchange Membrane Water Electrolyzers: A Comprehensive Review

ABSTRACT A proton exchange membrane water electrolyzer (PEMWE) represents one of the most promising technologies for green hydrogen production. Within the membrane electrode assembly (MEA), the interface between the porous transport layer (PTL) and the catalyst layer (CL) exerts a decisive influence on overall electrolyzer performance. The PTL–CL interface governs not only electron conduction efficiency and ohmic contact resistance, but also proton transport, oxygen bubble evacuation, liquid water supply, and the utilization of catalytically active sites. This review systematically examines the functional roles and resistance sources at the PTL–CL interface, and surveys recent advances in noble metal and non‐noble metal coatings, mechanical and chemical surface treatments, assembly compression optimization, microporous layer (MPL) and gradient porous structures, wettability engineering, and CL microstructure and composition optimization. Further discussion addresses future challenges including interfacial durability under ultra‐low iridium (Ir) loading, standardization of accelerated stress test (AST) protocols, and scale‐up manufacturing and engineering integration. This review aims to provide guidance for the design of high‐performance, low‐cost PTL–CL interfaces with practical scale‐up potential in PEMWE.