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Carbon black (CB), which has been widely used as a catalyst support, has been treated by various activation processes in order to increase the surface area. High-surface-area CB has a high pore volume in the primary particles. The degree of ionomer impregnation in the nanosized pores is able to be evaluated by the hysteresis volume, which is calculated from N2-adsorption analysis. We investigated the effect of distributions of both Pt and ionomer on the surface of CB support nanopores on the cell performance and durability of cathode catalyst layers with catalysts using CB with various nanopore volumes for polymer electrolyte fuel cells. The optimum ionomer content is affected by the nanopore volume, and the excess ionomer was found to block the entrances of the nanopores. For maximizing the cell performance and durability, we found that a high-surface-area CB was beneficial for achieving decreased Pt particle size, and the ionomer content was optimized to prevent the blocking of the nanopores. Improvement of the transport of oxygen and protons to Pt in the nanopores and increase in the interparticle distance led to both increase in the electrochemical surface area and suppression of Ostwald ripening and coarsening.
Kobayashi et al. (Thu,) studied this question.