Identical‐Location SEM Tracking of Pt/C Gas Diffusion Electrode Degradation at Fuel‐Cell‐Relevant Current Densities

Understanding Pt/C catalyst degradation under relevant proton‐exchange membrane fuel cell (PEMFC) conditions remains challenging because most identical‐location studies are conducted under nonrepresentative conditions (rotating disk electrode), configurations at low current densities. In this work, we combine a gas diffusion electrode platform with identical‐location scanning electron microscopy (IL‐SEM) to track morphological changes in Pt/C catalysts during accelerated stress testing while evaluating oxygen reduction reaction (ORR) performance at fuel‐cell‐relevant current densities (up to ∼1 A cm −2 ). Reliable relocation of identical sites is achieved using unique crack patterns in the gas diffusion electrode (GDE) catalyst layer as intrinsic markers. IL‐SEM imaging before and after electrochemical treatment reveals Pt nanoparticle restructuring after 10,000 accelerated stress test (AST) cycles, whereas no detectable morphological changes are observed after the initial break‐in procedure. Higher resolution IL‐SEM shows environment‐dependent degradation pathways, with isolated particles predominantly undergoing dissolution/redeposition and particle‐rich regions more frequently exhibiting detachment/agglomeration. Within the resolution and depth sensitivity of SEM, no clear morphological changes are detected in the carbon support. Complementary transmission electron microscopy (TEM) particle‐size analysis shows depletion of the smallest Pt particles after AST, consistent with their dissolution and subsequent redeposition onto larger particles. These results demonstrate that the combined IL‐SEM/GDE approach provides a route for directly identifying nanoscale degradation mechanisms under electrochemical conditions substantially closer to real fuel‐cell operation.