A model for mixed potential in direct methanol fuel cell cathode

We report a model for performance of the cathode catalyst layer (CCL) in a DMFC. Analytical solutions for the CCL polarization voltage and for the specific voltage loss due to methanol crossover (mixed potential) are obtained. The methanol–oxygen reaction in the CCL decreases the local oxygen concentration in the electrode, thereby raising the local overpotential and increasing the oxygen flux in the CCL. For typical parameters, the mixed potential peak of 150–200 mV is reached at the current density of 10–50 mA cm−2. A key parameter of crossover, which determines the value of mixed potential can be measured using the half-cell impedance spectroscopy.

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► Poor oxygen transport in the CCL of DMFC increases the activation polarization ηmixed.
► Analytical equation for ηmixed is derived.
► ηmixed has a peak of 100–150 mV at the cell current of 20–50 mA cm−2.
► Impedance spectroscopy can be used to measure the key crossover parameter.