Optimizing Ionomer Coverage in Solid Carbon-Supported Catalyst toward High Performance for Proton Exchange Membrane Fuel Cells

The three-phase interface comprising the carbon support, ionomer, and Pt nanoparticles was the main place where the cathode oxygen reduction reaction (ORR) occurred, determining the performance of the proton exchange membrane fuel cell (PEMFC). However, the unresolved transport issues taking place in the three-phase interface always bring about a much lower PEMFC performance and result in a lower utilization rate of Pt particles. In this study, we fabricated three different oxygen (O), nitrogen (N), and sulfur (S) surface-functionalized solid carbon catalysts (Pt/X–C, X = S, O, N) and investigated the ionomer distribution around the catalyst on the proton transfer resistances. Rotating disk electrode results demonstrated that the intrinsic activity of the surface-functionalization catalysts for the ORR was similar. However, as assembled as a membrane electrode assembly, the voltage of Pt/N–C was 0.522 V at 2000 mA cm–2 and 20% relative humidity (RH), which significantly outperformed those of Pt/C, Pt/S–C, and Pt/O–C, as 0.410, 0.467, and 0.479 V. Theoretical calculations and the dry proton accessibility results revealed that the N-functionalization catalyst can effectively improve the distribution of the ionomer on the catalyst surface and the utilization rate of the catalyst. Finally, the durability of the as-prepared catalysts was further evaluated via an accelerated durability test, and the voltage loss of Pt/N–C was only 21.7 mV at 2000 mA cm–2.