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The influence of hot-pressing temperature on catalytic activity and the performance of proton exchange membrane fuel cells (PEMFCs) was investigated using current-voltage (I-V) polarization, electrochemical impedance spectroscopy (EIS) and cyclic voltammetry (CV). EIS provided detailed information on the contribution, from high to low frequencies, of internal impedance (R s ), interfacial impedance (R if ) and reaction impedance (R rxn ). The ohmic resistance of the cell (R X ) was estimated from the I-V diagram for comparison with the R s and R if impedances. The R if is useful for diagnosing catalytic activity and interpreting PEMFC performance. A cell was hot-pressed at 125°C (near the transition temperature of Nafion), an optimum temperature for lowest ohmic resistance and total impedance in response to a maximal catalyst-specific activity.

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