Membrane transport phenomena in a Polymer-Electrolyte-Fuel-Cell

The developement of Polymer-Electrolyte-Fuel-Cells (PEFC) is a promising approach to meet the increasing energy requirement of the growing world population. This kind of fuel cells is especially suited for application in electric vehicles. An essential part of a PEFC is the proton conducting ion exchange membrane in between the gas diffusion electrodes. Important for the performance of the fuel cell is a high conductivity of the membrane. In addition to the proton transfer there is also a water flux across the membrane. This flux results from coupling of proton and water transport and from a gradient in the water content of the membrane. In this work a model for the transport of protons and water in a solid polymer electrolyte is presented. It is based on concentrated solution theory and takes into account the interrelationship between water and proton transport. In combination with the equations of change for the membrane phase, drying of the membrane and the resulting decrease in conductivity can be simulated. The membrane model was implemented in MODUSIM [1] a tool for modular simulation. Thus it was easy to combine the membrane module with appropriate modules for electrode reactions and transport in the gas diffusers to describe the dynamic behaviour of an electrode-membrane-electrode unit, i.e. current-voltage characteristics, water balance and heat transfer.