Small fuel cells water management

It is favorable for fuel cell operation when reduced methanol transport across the membrane is accompanied by proper water management. In particular, a low water crossover from the anode to the cathode is necessary to avoid flooding of the cathode. The dependence of water permeation on the membrane thickness is weak. Only a small decrease in water permeation is observed for the commercial Nafion membranes, whereas the thickness of the recast membranes has no significant influence on the water transport rate. In contrast, the effect of temperature on water permeation is strong. At 65°C, the rates are higher by a factor of 5 compared to those at 25°C. 

The thermal management requirements for small PEM fuel cells (and other PEM fuel cells as well) are intimately associated with water management. As discussed above, the level of hydration of the electrolyte membrane must be maintained in order to prevent dryout and thus loss of proton conduction in the membrane. The temperatures within the stack must accordingly be restricted. Cooling of the individual cells of the stack is carried out to assure that temperatures are moderate and rather uniform throughout the stack. 

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