Analysis of Proton Transport in Pseudo Catalyst Layers

Analytical techniques were investigated for examining the influence of the ionomer network structure on proton transport in the catalyst layers of a polymer electrolyte fuel cell. Two samples were made with and without a pseudocatalyst layer (PCL) consisting of a carbon black support and an ionomer between two membranes. The overall resistance of the samples was evaluated with a hydrogen pump technique. The difference in resistance between them was mainly due to the proton-transport resistance of the PCL. Another technique of subtracting high frequency resistance from the overall resistance was also examined. Almost the same characteristics were obtained with both techniques. Using the former technique, the effective proton conductivity of PCLs with different carbon supports was investigated. The effective proton conductivities differed. An analysis of the difference revealed the following two possible causes. One is that the Bruggeman factor of the samples might have been affected by the state of ionomer coverage. Another is that the proton conductivities of the ionomer as bulk differed, which might have been due to a difference in water content attributable to the carbon supports.