The three-dimensional (3D) distribution and oxidation state of a Pt cathode catalyst in a practical membrane electrode assembly (MEA) were visualized in a practical polymer electrolyte fuel cell (PEFC) under fuel-cell operating conditions. Operando 3D computed-tomography imaging with X-ray absorption near edge structure (XANES) spectroscopy (CT-XANES) clearly revealed the heterogeneous migration and degradation of Pt cathode catalyst in an MEA during accelerated degradation test (ADT) of PEFC. The degradative Pt migration proceeded over the entire cathode catalyst layer and spread to MEA depth direction into the Nafion membrane.

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A dependence of structural transformation and iron exsolution on chemical environment and reducing conditions is proven for the perovskite La0.6Sr0.4FeO3−δ.

Catalyst degradation at the cathode of a membrane electrode assembly (MEA) remains a critical issue for practical polymer electrolyte fuel cell (PEFC) operation, but such wet systems impede detailed visualization of degradation events in the cell during its operation. In this work, for the first time, operando spectroimaging (X-ray absorption near-edge structure−computed tomography) was used to produce clear three-dimensional (3D) images of the morphology, Pt and Co distributions, Co/Pt atomic ratio, and Pt valence state of a Pt−Co/C cathode catalyst in a PEFC MEA before and after performing a PEFC-accelerated degradation test. The infographic approach combining the operando spectroimaging and unsupervised learning of the 3D images revealed a catalyst degradation mechanism with different degradation behaviors for Pt and Co in the bimetallic catalyst and negligible migration of the Pt catalyst in local parts of the MEA.