Physical Properties of the Catalyst Layer in Proton Exchange Membrane Fuel Cell

The catalyst layer (CL) in proton exchange membrane fuel cells (PEMFC) is a composite material comprised of carbon-supported Pt bonded with proton-conductive ionomer. Resistances associated with processes in the CL, e.g. proton conduction through the ionomer percolation within CL, contribute to the voltage loss during the fuel cell operation. In this study, we attempt to characterize CLs from several aspects ^[1].

A DSC study was carried out to investigate the possible component interactions in the CL. As shown in Fig.1, in a nitrogen environment, an endothermic peak appeared around 100ºC for a dried Pt/Vulcan and Nafion mixed catalyst ink and at 135ºC for a Pt/Nafion mixture. However, this peak was not observed in a Carbon/Nafion mixture implying distinct interactions between each component. TEM was also adopted to further investigate the microstructure of CLs.

Moreover, the proton conductivity of CL using Nafion and BPSH as ionomer were measured respectively via the method proposed by Liu et al^[2]. The effects of ionomer/carbon ratio relative humidity and ionomer equivalent weight on CL proton conductivity, will be discussed.

Reference:

[1]H. Iden, A. Ohma, and K. Shinohara, “Analysis of Proton Transport in Pseudo Catalyst Layers,” Journal of The Electrochemical Society, vol. 156, no. 9, p. B1078, 2009.

[2] Y. Liu et al., “Proton Conduction and Oxygen Reduction Kinetics in PEM Fuel Cell Cathodes: Effects of Ionomer-to-Carbon Ratio and Relative Humidity,” Journal of The Electrochemical Society, vol. 156, no. 8, p. B970, 2009.