Quantitative analysis of cathode polarization in a direct methanol fuel cell employing a methanol-tolerant Fe-N-C-type catalyst

Direct methanol fuel cells (DMFCs) employing platinum-group-metal-free cathode catalysts can mitigate mixed-potential losses caused by methanol crossover. In this study, a PGM-free Fe-N-C-type catalyst, denoted CA, with high oxygen reduction reaction activity and negligible methanol oxidation activity was applied to a DMFC cathode. Rotating-disk-electrode measurements demonstrated high methanol tolerance and electrolyte-dependent non-Tafel polarization. DMFCs with the CA cathode maintained high cell voltages at methanol concentrations up to 10 M. A semi-empirical model, E c = E 0 − a i b ln( i/i *)[1 + ( i/c ) d ], was developed to describe cathode polarization over the full current-density range. For a representative condition, the proposed model reduced the root-mean-square error (RMSE) to 5.59 mV, compared with 33.10 mV for the i b -only model and 11.10 mV for a generalized conventional limiting-current model. The proposed model also yielded the lowest corrected Akaike information criterion (AICc) in 31 of the 35 datasets examined. Systematic variations in catalyst loading and operating conditions indicated that a and b primarily characterize baseline polarization, whereas c and d describe additional high-current polarization. The strong dependence on catalyst-layer thickness and oxygen availability indicates an important contribution of oxygen transport. Bootstrap analysis revealed parameter covariance, supporting the interpretation of the parameters as coupled, condition-dependent descriptors.