Postmortem thickness and morphology studies on a degraded membrane electrode assembly ͑MEA͒ caused by carbon corrosion under a local H 2 starvation operation in a proton exchange membrane ͑PEM͒ fuel cell were carried out using optical, scanning, and transmission electron microscopy. Samples used for the postmortem studies were selected and indexed with the aid of a limiting current density distribution map that was premeasured from the degraded MEA using an electrochemical diagnostic technique. An explicit correlation was found between the postmortem studies and the diagnostics: where the electrode structure damage ͑i.e., thickness reduction and porosity collapse͒ is significant, the limiting current density is low. The structure damage and current density drop were found to be in the H 2 -starved region where the carbon corrosion is severe. The results presented here are of significance in understanding the fundamentals of carbon corrosion mechanism and related structural origin of fuel cell performance degradation.

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A technique is described for determining the source and degree of electrodes degradation in membrane electrode assemblies (MEAs) from proton exchange membrane fuel cells. This technique is nondestructive and provides spatial resolution across the MEA's active area. The degradation modes that are considered are the oxygen reduction activity loss through either electrochemically active area or mass activity loss, increased gas transport resistance from corrosion of the catalyst's carbon support, and the increased protonic transport loss through chemical degradation of the electrode layer's ion‐conducting polymer. A current distribution tool is used with cyclic voltammetry and polarization curves to isolate each of the primary sources of voltage degradation. Results of new MEAs are presented first to demonstrate the approximate resolution of the test method. Then results are presented for MEAs that were aged in a model test to cause carbon corrosion in the cathode layer via localized anode starvation. These include follow‐up materials characterization, where it is shown that the results of this electrochemical diagnostic correlate well with postmortem materials characterization. Finally, results are shown for a part aged in a model start‐up/shutdown aging test and compared with modeling results to explain the spatial characteristics of the observed degradation.

A non-destructive, diagnostic technique for evaluating the extent of degradation in electrodes on membrane-electrode assemblies (MEAs) has been developed that can be applied to parts from application-scale proton exchange membrane fuel cells. The modes of electrode degradation that are examined include: catalyst activity loss, catalyst area loss, and electrode support structure damage through carbon corrosion. The technique incorporates a current distribution tool to enable spatially resolved analysis at a length scale of approximately 1 cm. The MEA parts are evaluated through a combination of cyclic voltammetry and polarization curves performed at conditions designed to expose degradation in one of the modes described above.