An Algebraic Model of Liquid Feed Direct Methanol Fuel Cell with Co-Current Channel Flow

概要

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Algebraic equations of a liquid feed direct methanol fuel cell (DMFC) with co-current channel flow are derived to correlate the literature experimental discharge data with the theoretically predicted polarization curve. Mass conservation of methanol and oxygen normal to the membrane electrode assembly is derived and an averaging procedure over the channel length is carried out to give the overall cell performance. The influence of methanol crossover through the membrane is described as the result of diffusion, electro-osmotic drag, and the pressure difference induced permeation between anode and cathode. The influence of permeated methanol on the cathode electrode potential is demonstrated by the mixed potential theory. That is, the parasitic methanol oxidation reaction consumes part of the oxygen reduction current in the cathode catalyst layer, forming an internal short circuit, so that the resultant cell current density is less than the case without crossover. This model is capable of predicting the concentration depletions of methanol and oxygen within the porous diffusion media of the membrane electrode assembly, and that along the respective flow channels. A nonlinear least square scheme, coupled with an algebraic model, retrieves the parameters of methanol diffusivity in the anode backing layer, exchange current density of methanol on the anode catalyst surface, and proton conductivity in the polymer electrolyte membrane.
2009-07-01