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We present here an isothermal, one-dimensional, steady-state model for a complete polymer electrolyte fuel cell (PEFC) with a 117 Nation | membrane. In this model we employ water diffusion coefficients electro-osmotic drag coefficients, water sorption isotherms, and membrane conductivities, all measured in our laboratory as functions of membrane water content. The model pre.dicts a net-water-per-proton flux ratio of 0.2 H20/H § under typical operating conditions, which is much less than the measured electro-osmotic drag coefficient for a fully hydrated membrane. It also predicts an increase in membrane resistance with increased current density and demonstrates the great advantage of a thinner membrane in alleviating this resistance problem. Both of these predictions were verified experimentally under certain conditions.Fuel cells employing hydrated Nation or other hydrated perfluorinated ionomeric materials as the electrolyte are promising candidates for electric vehicle applications (1). The polymer electrolyte provides room temperature startup, elimination of many corrosion problems, and the potential for low resistance losses. Resistive losses within the fuel cell result, in part, from the decrease of membrane protonic conductivity following partial dehydration of the membrane. On the other hand, cathode flooding problems are caused when too much water is in the system. Clearly, water management within the fuel cell involves walking a tightrope between the two extremes.Spatial variations of water content within the polymeric electrolyte of a current~carrying fuel cell result from the electro-osmotic dragging of water with proton transport from anode to cathode, the production of water by the oxygen reduction reaction at the cathode, humidification conditions of the inlet gas streams, and "back-diffusion" of water from cathode to anode, which lessens the concentration gradient.The water distribution within a polymer electrolyte fuel cell (PEFC) has been modeled at various levels of sophistication by several groups. Verbrugge and Hill (2-4) have carried out extensive modeling of transport properties in perfluorosulfonate ionomers based on dilute solution theory. Fales et al. (5) reported an isothermal water map based on hydraulic permeability and electro-osmotic drag data. Though the model was relatively simple, some broad conclusions concerning membrane humidification conditions were reached. Fuller and Newman (6) applied concentrated solution theory and employed literature data on transport properties to produce a general description of water transport in fuel cell membranes. The last contribution emphasizes water distribution within the membrane. Boundary values were set in these cases rather arbitrarily. A different approach was taken by Bernardi (7). She considered transport through the gas diffusion electrodes, assuming the membrane to be uniformly hydrated, corresponding to an "ultrathin membrane" case.We present an isothermal, one-dimensional, steady-state model for water transport through a co...