1D+1D model of a DMFC: localized solutions and mixedpotential

Our 1D + 1D model of DMFC reveals a new effect. At infinitely small total current in the cell, near the channel inlet forms a "bridge", a narrow region with finite local current density. The bridge short-circuits the electrodes, thus reducing cell open-circuit voltage. In our previous work the effect is described for the case of equal methanol lambda(a) and oxygen lambda(c) stoichiometries. In this Letter, we analyze the general case of arbitrary lambda(a) and lambda(c). In the case of lambda(a) > lambda(c) current may occupy finite domain of the cell surface. Asymptotic solution for the case of lambda(a) much greater than lambda(c) shows, that the size of this domain is proportional to oxygen stoichiometry. In the opposite limit of lambda(a) much greater than lambda(c) local current exponentially decreases with the distance along the channel. Asymptotic solutions suggest that the bridge forms regardless of the relationship between lambda(a) and lambda(c). In all cases local current density in the bridge increases with the rate of methanol crossover and decreases with the growth of the "rate-determining" stoichiometry. The expression for voltage loss at open-circuit is derived. (C) 2004 Elsevier B.V. All rights reserved.