Fuel cell applications, membrane requirements methanol crossover

Such bimetallic alloys display higher tolerance to the presence of methanol, as shown in Fig. 11.12, where Pt-Cr/C is compared with Pt/C. However, an increase in alcohol concentration leads to a decrease in the tolerance of the catalyst [Koffi et al., 2005 Coutanceau et ah, 2006]. Low power densities are currently obtained in DMFCs working at low temperature [Hogarth and Ralph, 2002] because it is difficult to activate the oxidation reaction of the alcohol and the reduction reaction of molecular oxygen at room temperature. To counterbalance the loss of performance of the cell due to low reaction rates, the membrane thickness can be reduced in order to increase its conductance [Shen et al., 2004]. As a result, methanol crossover is strongly increased. This could be detrimental to the fuel cell s electrical performance, as methanol acts as a poison for conventional Pt-based catalysts present in fuel cell cathodes, especially in the case of mini or micro fuel cell applications, where high methanol concentrations are required (5-10 M). 

With the introduction of proton conducting membranes, interest in direct methanol fuel cells (DMFC) systems in the 1990s has been renewed with projects in North America, Japan, and Europe. Of particular significance has been the work of Los Alamos National Laboratory. If the power density required for vehicle applications is to be achieved, further improvements to anode performance are necessary. Existing membranes also allow methanol crossover, which in turn contributes to poor cell performance. hi this context, it is interesting to speculate on how high-temperature membranes such as that developed by Celanese would perform in a direct methanol fuel cell. 

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