Regulating sulfonic acid group adsorption for enhanced oxygen reduction reaction activity at Pt(111)-Nafion

To elucidate the structure–performance relationship of membrane electrode assemblies in proton exchange membrane fuel cells, we construct well-defined Pt(111)-Nafion model interfaces and systematically investigate the effects of preparation parameters (processing temperature and film thickness) and solution pH on the interfacial structure and oxygen reduction reaction (ORR) activity. Our findings reveal a distinct linear correlation between ORR activity and both the adsorption potential and the quantity of terminal sulfonic acid groups in Nafion. Specifically, a higher adsorption potential and a lower adsorption quantity of sulfonic acid groups correspond to enhanced ORR activity. These results underscore the crucial role of the shielding effect induced by sulfonic acid group adsorption, which is significantly influenced by solution pH and preparation conditions. Lowering the processing temperature, reducing the film thickness, or decreasing the solution pH effectively improves ORR performance. Furthermore, we introduce a poison control strategy by incorporating trace amounts of Br⁻ into the solution. This approach weakens the shielding effect of adsorbed sulfonic acid groups without significantly poisoning the interface, thereby further enhancing ORR activity. Our study provides valuable insights for the rational design and optimization of electrocatalytic systems for energy conversion and storage applications.