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The Effect of Methanol Crossover on the Cathode Overpotential of DMFCs

The effects of methanol crossover on cathode overpotential of direct methanol fuel cells (DMFCs) were investigated by focusing on a mixed potential effect and surface poisoning of the catalyst. Experiments using different membranes and catalyst loadings were performed and compared with a semi‐quantitative model to discuss the main cause of the cathode overpotential. When the measured methanol crossover increased, cathode overpotential increased at particular threshold values, which were 150 mA cm–2 at 0.3 mg cm–2 of cathode platinum (Pt) loading and above 200 mA cm–2 at 1.1 mg cm–2. The modelling results also supported this tendency, and showed that Pt surface was poisoned to a great extent above the threshold methanol crossover where the cathode overpotential increased sharply, while the cathode overpotential remained low and was explained solely by the mixed potential below the threshold value. The threshold methanol crossover can be regarded as the acceptable value, below which the cathode overpotential from methanol crossover remains low, and was related with the Pt loading in the cathode. The reduction of methanol crossover through membranes below the acceptable values will contribute greatly to a decrease in the cathode overpotential and to the reduction of catalyst loadings.