Operando DRT insights into degradation of porous transport layers under intermittent accelerated stress tests in PEM water electrolyzer

The porous transport layer (PTL) is crucial in proton exchange membrane water electrolyzers (PEMWEs), facilitating mass transport and maintaining strong PTL-catalyst layer (CL) contact. However, PTL degradation limits operational lifetime and cost-effectiveness. Previous studies often rely on ex-situ methods, lacking rapid diagnostics for degradation pathways. This study employs operando Distribution of Relaxation Times (DRT) to diagnose PTL-induced degradation by tracking estimated resistances associated with characteristic relaxation times. Three PTLs—carbon paper with microporous layer (C-MPL), uncoated Ti felt (u-Ti), and Pt-coated Ti felt (Pt–Ti)—were investigated under intermittent accelerated stress tests (ASTs) involving low- and high-load cycling (1-0 and 3-0 A/cm 2 ). SEM-EDS and interfacial contact resistance (ICR) further confirmed microstructural damage and contact losses. C-MPL showed a 15-fold rise in mass transport resistance under high-load AST, while oxidized u-Ti exhibited increased contact resistance. Operando DRT serves as a rapid diagnostic tool for PTL selection and quantifying degradation in AST protocols.