The effect of residual water content in the MEA on performance degradation caused by repeated startup of a frozen cell at -30°C was investigated. The results indicated that in case the residual water content in the MEA was low, a condition occurred in which both diffusive and electrochemical activation capability of the ionomer in the catalyst layer of the cathode significantly declined and performance degradation increased compared with the high residual water content. Significant functional decay of the polymer electrolyte membrane was not measured. Presumably, dry operation of the cell during startup from a frozen state caused the decline in ionomer performance, resulting in degraded cell performance.
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