Beyond cell voltage: Workflow for evaluation of PGM-free HER catalysts in PEM water electrolysis

Proton exchange membrane water electrolysis (PEMWE) requires efficient platinum group metal (PGM)-free catalysts for green hydrogen production. Herein, we present a workflow for evaluating hydrogen evolution reaction (HER) catalysts under application relevant PEMWE conditions using pentlandites as model compounds. Among the investigated materials, Co 6 . 75 Ni 2 . 25 S 8 exhibited the best device-level performance, delivering competitive cell voltages (2.03 V at 1 A cm −2 ) and stable hydrogen production. Our post-mortem workflow using ICP-OES, SEM/EDX, PXRD and XPS revealed increased catalyst dissolution and Co/Ni migration into the membrane compared to Pt. Distribution of relaxation times (DRT) analysis identified the kinetic, transport and degradation processes governing cell operation. Continuous operation appeared beneficial compared to intermittent operation regarding degradation. The proposed workflow distinguishes electrochemical performance from structural stability via cross-validation of orthogonal methods, providing a decision framework for assessing the industrial applicability of emerging PGM-free HER catalysts and guiding protocol development and further optimization for durable PEMWE operation.