Theory for water management in membranes for polymer electrolyte fuel cells Part 1. The effect of impurity ions at the anode side on the membrane performances

摘要

Water management was discussed theoretically for membranes in polymer electrolyte fuel cells in which the polymer electrolyte membranes were contaminated with foreign impurity cations. Water transport in a contaminated two-cation system membrane was considered by assuming an 'infected zone' of finite thickness, a hypothetical layer of mixed cations, H~+ and the contaminant ions Q~(n+), stretching from the catalyst layer|membrane interface into the membrane. Solving the flux equation of water with some boundary conditions, the water concentration profile across the membrane was derived in analytical form. Some characteristic variables such as water content, the net water flux and the membrane resistance overvoltage were calculated systematically as functions of several relevant parameters in fuel cell operations. It was discovered theoretically that both the current density and the membrane thickness are vital parameters in the management of water in fuel cell membranes, and this tendency becomes larger when the membrane is contaminated by impurity ions, especially when such ions are localized at the anode|membrane interface. It is noted from the point of view of water management that special caution should be directed in order to protect the membrane from contamination.