Methanol crossover effect for direct methanol fuel cells: Applicability of methanol activity in polymer electrolyte membrane

We developed a cell voltage model as a function of the current density response of the direct methanol fuel cell (DMFC). The impact on cell performance by methanol crossover, which lowers the cell performance, is discussed. We employ a srmethanol activity term to take into account the methanol crossover effect. A methanol activity equation is derived from the Helmholtz energy of mixing. In this study, we use a simplified expression of the Helmholtz energy of mixing and correct the mathematical approximation defect using the fractional form. To take the specific interaction into account, a secondary lattice concept, perturbation to a fixed reference system, is introduced. A cell voltage equation with reasonable boundary conditions, including a methanol crossover effect that plays a major role in determining the cell voltage of DMFC, is developed. It can also be found that the methanol crossover increases with an increase in membrane chain length. (c) 2007 The Electrochemical Society.