Analysis of PEMFC freeze degradation at −20 °C after gas purging

Proton exchange membrane fuel cell (PEMFC) freeze degradation was investigated using 20 freeze/thaw cycles of two cells with gases purged immediately after operation. The cell purged by gas with an RH 58.0% at 25 °C was found to have no performance loss after the 20 freeze/thaw cycles. From the cell resistances and the electrochemical impedance spectra (EIS), the electrolyte conductivity and interfacial charge transfer resistance were unchanged. The electrochemical active surface area (ECSA) from the cyclic voltammetry (CV) measurements indicated that the amount of water in the catalyst layer of the cell was reduced to an extent that the damage in the freeze/thaw cycles was avoided. Another cell was purged by RH 64.9% gas in the first cycle, and then was purged with RH 45.0% gas in 19 freeze/thaw cycles. Although the cell easily became flooded at high current densities after the first cycle, no further performance loss was found. The pore size distribution data from mercury intrusion porosimetry measurements suggested that the gas diffusion layer was changed by the first freeze cycles. The micrographs (SEM) further proved no membrane electrode assembly (MEA) delamination. These results shed some light on the relationship of the water amount in the cell to subzero temperature exposure.