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A study of water crossover in polymer electrolyte membrane fuel cells Yau, Tak Cheung


Water crossover between anode and cathode of polymer electrolyte membrane fuel cells has been studied together with fuel cell performance at steady state. The parameters considered included temperature, pressure, inlet humidity and the presence of a cathode microporous layer. In general water crossover was found to be increasingly toward the anode side with increasing current density up to a certain point beyond which a plateau was observed. Larger cathode-to-anode inlet humidity gradient, lower temperature and higher cathode pressure enhanced water crossover to the anode, due to a higher downstream humidity at the cathode catalyst layer. The presence of a cathode microporous layer enhanced water crossover to the anode only when the cathode inlet humidity was low. It was proposed that this layer imposed a larger diffusion barrier between the cathode channel and the membrane interface whose effects diminished at high relative humidity. The zero crossover rate under zero humidity gradients with no load regardless of the presence of the cathode microporous layer suggested that capillary action was not a contributing factor for the action of the layer. In addition, the quantitative data obtained by the water crossover measurement equipment were found to be useful in model validation and parameter estimations. The data could pinpoint inadequacies in models, as well as providing estimated parameters that were more consistent with changes in the oxygen concentration and fitted better to both the current density and water crossover data given a certain voltage.

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