It is commonly agreed upon that the transport properties of PEMs have a great effect on fuel cell performance. These include proton conductivity, ion mobility, reactive and inert gas solubility and diffusivity, water transport due to concentration and pressure gradients, and electroosmotic drag. Despite this there are widely different methods used to obtain these properties, and even greater differences in reported numbers.

Much of the difficulty in reaching agreement on transport numbers lies in the difficulty of defining the polymers themselves. Small changes in temperature or relative humidity can lead to large changes in transport properties, especially conductivity and water transport. The membranes water content is also a strong function of these conditions, and therefore the dimension of the polymer is also changing. Compounding difficulties is the fact that the thermal and hygral history greatly affect structure on the nano scale, and also have a strong impact on these properties.

This talk looks at the different transport phenomena in PEMs, there relative influence on fuel cell performance, methods that have been used to measure them, and common errors that are made. It also focuses on some unsolved questions, or areas of open debate in the fuel cell community, such as does diffusivity differ when a membrane is hydrating and expanding, compared to when it is dehydrating or contracting? Can the electroosmotic drag coefficient decrease below unity? Is transport greatly affected by ionomer thickness?