Tailoring the Pt/Ionomer Interface via Self-Assembly of C₇H₈S on the Pt Surface for Superior PEMFC Performance

Reducing the Pt loading at the cathode of proton exchange membrane fuel cells (PEMFCs) increases the local oxygen transport resistance in the catalyst layer (CL), severely degrading cell performance. To address this, tailoring the interface between platinum and the ionomer is an effective strategy to mitigate local oxygen transport resistance. In this study, a thin and uniform monolayer of −C7H7S groups was self-assembled on the Pt surface to prepare a Pt–C7H7S/C catalyst. The −C7H7S groups were then removed by cyclic voltammetry (CV) electrochemical methods to construct a new Pt–ionomer interface (M-Pt/ionomer). Elemental analysis confirmed that the −C7H7S groups were successfully assembled on the Pt surface and remained stable during the preparation of the membrane electrode assembly (MEA), and they were ultimately completely removed by CV electrochemical methods. Compared with the traditional Pt/C MEA (S-MEA), the modified MEA (M-MEA) exhibited a 20.3% increase in peak power and a 102 mV increase in voltage at 3000 mA/cm² when the cathode Pt loading was only 0.075 mg/cm². Limiting current measurements revealed that the local oxygen transport resistance of M-MEA decreased from 11.09 to 5.57 s/cm compared to S-MEA. It is believed that the increased hydrophobicity of the Pt–C7H7S/C catalyst inhibited the adsorption of the sulfonate groups in the hydrophilic phase of the ionomer on the Pt surface, thereby releasing active sites. Moreover, the loose adsorption of sulfonate groups on the Pt surface also relaxed the distribution of the ionomer backbone, thus enhancing local oxygen transport capability. Compared to S-MEA, M-MEA demonstrated superior performance under low-temperature and high-humidity conditions, which further verified that the M-Pt/ionomer interface has stronger water drainage capabilities than the traditional Pt/ionomer interface (S–Pt/ionomer), thereby improving local oxygen transport capability.