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When interdigitated gas distributors are used in a PEM

An along-the-channel model is developed for evaluating the effects of various design and operating parameters on the performance of a proton exchange membrane (PEM) fuel cell. The model, which is based on a previous one, has been extended to include the convective water transport across the membrane by a pressure gradient, temperature distribution in the solid phase along the flow channel, and heat removal by natural convection and coflow and counterflow heat exchangers. Results from the model show that the performance of a PEM fuel cell could be improved by anode humidification and positive differential pressure between the cathode and anode to increase the back transport rate of water across the roembrane. Results also show that effective heat removal is necessary for preventing excessive temperature which could lead to local membrane dehydration. For heat removal and distribution, the counterflow heat exchanger is most effective.

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Proper water management is vital to ensuring successful performance of proton exchange membrane fuel cells. The effectiveness of the direct liquid water injection scheme and the interdigitated flow field design towards providing adequate gas humidification to maintain membrane optimal hydration and alleviating the mass transport limitations of the reactants and electrode flooding is investigated. It is found that the direct liquid water injection used in conjunction with the interdigitated flow fields as a humidification technique is an extremely effective method of water management. The forced flow-through-the-electrode characteristic of the interdigitated flow field 1) provides higher transport rates of reactant and products to and from the inner catalyst layers, 2) increases the hydration state and conductivity of the membrane by bringing its anode/membrane interface in direct contact with liquid water, and 3) increases the cell tolerance limits for excess injected liquid water, which could be used to provide simultaneous evaporative cooling. Experimental results show substantial improvements in performance as a result of these improvements.