Optimizing ionomer distribution for constructing efficient Pt/ionomer interfaces: Research on improving the performance of low-platinum-loading hydrogen fuel cells

Reducing the platinum content within membrane electrode assemblies (MEAs) of proton exchange membrane fuel cells (PEMFCs) is a strategic approach to decrease their overall costs. Nevertheless, this approach can result in significant voltage losses which are primarily attributed to the increased impedance of oxygen through the Pt-ionomer interface. In this study, the local oxygen mass transfer resistance (R_O2-local) is effectively reduced by doping sulfur onto the carbon supports. The surface hydrophilicity of the carbon supports is enhanced after sulfur doping, which intensifies the interaction between the polar side chains of the ionomers and the carbon supports. This results in a more uniform distribution of the ionomers within catalyst layers, thus enabling oxygen diffusion to the Pt surface without passing through a dense ionomer layer. Moreover, the uniform distribution of ionomers reduces the adsorption of sulfonic acid groups on Pt, thereby mitigating their toxic effect. In low Pt-loaded MEAs, i.e., 0.03 and 0.1 mg·cm⁻² for anode and cathode, respectively, the sulfur-doped Pt/S-KB-1.0 catalyst demonstrates an effective Pt utilization of 0.098 g_Pt·kW⁻¹ on the cathode side, and a 24.8 % decrease of R_O2-local compared to the undoped sample. Additionally, it exhibits favorable low-humidity adaptability and superior durability performance.