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Degradation is one of the critical issues of direct methanol fuel cells. The experimental investigations found in the literature show that degradation has both permanent and temporary contributions. The latter can be recovered after operation interruption, but its origins are not fully understood. This work aims to investigate the anodic degradation by measuring the anode overpotential setting the cathode as a dynamic hydrogen electrode. Experimental degradation tests are performed in cycling operation, which consists in cycles of 20 min of continuous operation at constant current and a variable number of minutes at OCV. Experimental results show that the anode overpotential decreases after OCV period, demonstrating the existence of anode temporary degradation. Moreover the temporary contribution is strongly affected by the duration of OCV period: long operation interruption lowers temporary degradation. From the interpretation of impedance spectra, it is reasonable to attribute the anode temporary degradation mainly to the dehydration of the anode electrode and the reduction of methanol concentration due to CO2 accumulation that determines a gas diffusion layer and electrode saturation reduction. Instead hydrogen crossover from cathode to anode has a negligible effect. Finally, a physical model of anode impedance is used to support the proposed origins of anode temporary degradation.

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