Influence of the Pt/ionomer/water interface on the oxygen reduction reaction: insights into the micro-three-phase interface

Understanding the Pt/ionomer/water interface structure and its impact on the oxygen reduction reaction (ORR) activity is essential for enhancing catalyst utilization and performance of fuel cells. This study aimed to investigate the influence of sulfonic acid groups on the Pt/ionomer/water interface and the ORR mechanism. By using a combination of DFT, AIMD, and microkinetic simulations, the results showed that when the sulfonic acid group is located at the edge of the Helmholtz plane, it creates an optimal three-phase interface, providing more available active sites, a stronger interfacial electric field, and a more continuous H-bond network. This configuration results in the *OOH dissociation becoming the rate-determining step, demonstrating significantly higher intrinsic ORR activity with a much lower theoretical overpotential of 0.11 V. Conversely, when the sulfonic acid group is in contact with the Pt surface, it causes the Pt surface's d-band center to shift down, weakens the interfacial electric field, and disrupts the H-bond network, resulting in a blocking effect on the ORR with an overpotential of 0.23 V. These insights shed light on the role of solid-solid-liquid interfaces in the ORR performance and provide valuable information for the rational design of catalyst interfaces.