Nano-scale structures of catalyst and catalyst layer in PEFC are especially the important factors governing their ORR activity and efficiency because the formation of effective reaction sites and the mass transfer of both reactants and products are finally tuned via the nano-scale structure inside catalyst layer. However, the pore structure in the catalyst layers is still constructed by the inter-particle structure of catalyst supports, such as Vulcan, during preparation of the general membrane electrode assembly, and these are very complicated processes. As a result, precise control of both the pore structure and pore size in the nano/meso-scale becomes very difficult. We have reported the effects of the nano-structure in catalysts on the ORR activity by measuring the reaction kinetics in the electrode constructed with model catalysts.In this report, to clarify the correlation between the ORR activity and Nafion distribution within the pores in a catalyst layer, a model catalyst layer was constructed. For this purpose, self-standing mesoporous carbon membranes were developed. The nano-structured model catalyst layer was prepared using the membranes, and Nafion diluted by various solvents was directly cast onto the membrane. Nafion distribution was measured using XPS-depth profiling method. From F1s signal in the XP spectra, the penetration of Nafion toward mesopores was confirmed, and the spatial distribution of Nafion was dependent on the kind of dispersant. Further, the kinetic ORR current at these model catalysts was also influenced by the kind of dispersant for Nafion. In the presentation, details about the pore size effect of catalyst layer on a Nafion distribution and ORR activity will be discussed. Furthermore, based on a comparison with kinetic limited current of an electrode prepared with and without Nafion, ORR activity of platinum particles depending on their locations will be discussed.

Analysis of correlation between catalyst nano-structures and their ORR activity: Synthesis of a model catalyst layer with novel mesoporous carbon membrane

243rd National Meeting (2012)

The official archive and repository for all ACS Meetings & Expositions abstracts and select posters or presentations.