The features of a direct methanol fuel cell cathode impedance due to methanol crossover: Modeling and experiment

We report a model for impedance of the cathode catalyst layer (CCL) of a DMFC. The model employs a non-Tafel rate of the methanol oxidation reaction (MOR) in the cathode and it takes into account diffusive transport of oxygen and methanol. Due to large MOR overpotential on the cathode side, the rate of this reaction is determined by the potential-independent methanol adsorption on the catalyst surface. According to the model, at all methanol concentrations, the presence of methanol in the CCL affects the low-frequency part of the spectrum. In addition, at high methanol concentration, a MOR-dominated domain (virtual anode) forms at the membrane interface. This domain manifests itself as a weakly pronounced second high-frequency arc. The model predictions are compared to the measured in-house and literature cathode spectra.