Several postmortem analyses were conducted to investigate the change of Pt distribution in the active components in a phosphoric acid fuel cell (PAFC) during a long‐term operation. Quantitative analysis of an electron probe microanalyzer (EPMA) indicates not only the loss of Pt in a cathode but also Pt migration to an anode during operation and identifies the Pt in a matrix. It was found that the behavior of Pt during cell operation is associated with operation mode and presumably subsequent singular distribution of phosphoric acid. Observation by transmission electron microscopy (TEM) demonstrates that Pt in an electrode near a matrix grows earlier than that of the center and backing paper side of an electrode. In addition to the results of Pt dissolution, a morphological consideration through TEM gives clear evidence that particle coalescence is also involved in particle growth as sintering mechanism.

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