Abstract

The performance of single-PEM fuel cells at sub-freezing temperatures has been characterized. Fully humidified fuel cells that were subjected to multiple freeze/thaw cycles down to -40 oC showed degradation in performance associated with mass transport problems at the gas diffusion layer. The performance loss was negligible for cloth GDLs and slow cooling rates while fast cooling rates and paper GDLs showed significant degradation. When a single-fuel cell was operated at -10 oC at a constant voltage, the current first increased to a maximum value, then started decaying due to ice formation. This ice formation was monitored using neutron radiography and was found to be concentrated near the inlets, outlets and cell edges resulting in a significant increase in mass transport resistance as revealed by AC impedance spectroscopy. Cyclic voltammograms at -10 oC show no change in catalyst electrochemical surface area associated with this decreased performance. Finally the cell did not exhibit any degradation in performance at 80 oC even after 5 separate operations at -10 oC, where the cell was allowed to completely clog with ice each time until no further current was produced.

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