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.