Effect of Pt and Ionomer Distribution on Polymer Electrolyte Fuel Cell Performance and Durability

Abstract

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.

Recent Advancements in the Synthesis and Application of Carbon-Based Catalysts in the ORR

“…This finding indicates that the catalyst should have most of the active sites on the external surface to maintain good high current density performance, with a small fraction inside the pores for protection from the ionomer poisoning for high mass activity [106]. Further, Kaobayshi et al [95] determined that catalysts with large nanopore capacities can utilize Pt in pores at an intermediate current density. There is a reduction in Pt poisoning because the number of Pt NPs not in contact with the ionomer increases.…”

“…Another factor in electrocatalytic performance is the pore size of the material. Pore sizes are classified as macropores (>50 nm in diameter), mesopores (2-50 nm in diameter), and micropores (<2 nm in diameter) as shown in Figure 7 [95]. Mesopores are considered the most advantageous pore size because the ionomer cannot interact with the Pt particle inside micropores, essentially making them unavailable [95].…”

“…Pore sizes are classified as macropores (>50 nm in diameter), mesopores (2-50 nm in diameter), and micropores (<2 nm in diameter) as shown in Figure 7 [95]. Mesopores are considered the most advantageous pore size because the ionomer cannot interact with the Pt particle inside micropores, essentially making them unavailable [95]. However, ORR kinetic activity can be poisoned by sulfate and phosphate anions, which are contained in the ionomer, meaning the ionomer must be in close proximity to the Pt without directly touching.…”

“…the most advantageous pore size because the ionomer cannot interact with the Pt particle inside micropores, essentially making them unavailable [95]. However, ORR kinetic activity can be poisoned by sulfate and phosphate anions, which are contained in the ionomer, meaning the ionomer must be in close proximity to the Pt without directly touching.…”

Effect of Pore Size of Carbon Support on Electrode Reaction Activity of Catalyst Layer in Polymer Electrolyte Fuel Cell: Reactive Molecular Dynamics Simulations

“…Moreover, the kb support with accessible pores was found to show higher electrode reaction activity than that with curved pores. kobayashi et al reported that in the case of the KB support with large pores at the cathode, the Pt nanoparticles in the large pores showed a higher effective surface area and a higher electrode reaction activity than those on other sites [2].…”