Testing of proton exchange composite membranes “polymer film-sulfounded polystyrene” in a direct methanol fuel cell at 60°C. Methanol crossover

The coefficients of diffusion permeability of methanol through the synthesized composite membranes “polymer film-sulfonated polystyrene” and Nafion-115 membrane were measured. For several composite membranes with significantly different transport properties the diffusion flux of methanol (qdiff) through these membranes was calculated under the conditions of a direct methanol fuel cell (DMFC) at 60°C and 1–2 M concentration of the feed solution. Direct measurements of the crossover current and methanol crossover (qCVA) in DMFC based on these membranes were carried out by using the cyclic voltammetry method (CVA). It has been established that the qCVA values are on average 15% lower than the corresponding qdiff values calculated for each membrane based on its individual parameters (area, thickness, methanol permeability coefficient). The observed ratio qCVAqdiff is proposed to be explained by the experimentally uncontrolled and, probably, incomplete oxidation of methanol at the cathode. Based on the obtained data, it can be concluded that without monitoring the degree of methanol oxidation at the DMFC cathode, the experimental values of the crossover qCVA can markedly differ from the calculated qdiff and the real values of the methanol crossover in the DMFC. A comparative study of performance of DMFCs based on synthesized composite membranes with significantly different transport properties and Nafion-115 membranes was carried out.It has been established that at 60°C and 1 M concentration of the feed solution, the methanol crossover value has practically no effect on the performance of the cells.