Joshua S. Preston

Consideration of the Role of Micro-Porous Layer on Liquid Water Distribution in Polymer Electrolyte Fuel Cells

Evidence of a region of gradual property change between the micro-porous layer and the macroporous layer of bilayer diffusion media is presented, and a mathematical model describing the effects of this gradual interfacial region is developed. The model results in a continuous liquid water saturation distribution across the diffusion media compared to the sharp discontinuity in the liquid phase saturation predicted by the earlier sudden interface models. High-resolution neutron radiography is used to measure the water content profile across the diffusion media, and the results are compared with the model predictions. The effect of the geometric blur, and uncertainty in-neutron radiography, is accounted for by applying the effects of geometric blur to model results. When the blur is considered, the neutron radiography results are found to be very similar to model predictions.

Water Transport Across a Polymer Electrolyte Membrane under Thermal Gradients

A fundamental experimental and numerical study of the water transport across a perfluorosulfonic acid membrane under a temperature gradient is presented. The water transport phenomenon was experimentally investigated through water flux measurement and neutron radiography. The experimental observations found that water is transported in the direction from the high temperature side to the low temperature side, when both sides of the membrane are sufficiently humidified, and suggest that the transport mechanism is concentration gradient driven. The neutron radiography measurements detected the presence of water content gradient across the membrane and higher water content is seen at a larger thermal gradient. A numerical model was developed to investigate the experimental results. Water transport predictions agreed qualitatively but more accurate material and transport property characterizations are needed for further improvement.