Pt/C Electrocatalysts with High Pt Density: A Case Study on Oxygen Reduction Performance from Rotating Disk Electrode to Membrane Electrode Assembly

For the economical deployment of proton exchange membrane fuel cells (PEMFCs), achieving both ultralow platinum (Pt) loading and superior catalytic performance at the membrane electrode assembly (MEA) level is paramount. Despite the significant advancements over the past decade in the development of potent Pt-based catalysts for the oxygen reduction reaction (ORR), the high activities documented using rotating disk electrode (RDE) evaluations often do not manifest comparably in MEA applications. In this study, we delved into the intricate interplay between the catalyst layer (CL) fabrication and its consequent MEA performance. Using a liquid-phase reduction method, we synthesized active Pt/C catalysts at varied loadings: 20 wt % Pt/C, 40 wt % Pt/C, and 70 wt % Pt/C. Intriguingly, even at the 70 wt % threshold, transmission electron microscopy and powder X-ray diffraction characterizations revealed a consistent distribution of Pt nanoparticles across the carbon substrate, coupled with an evident crystalline nature. This dispersion, in tandem with the desirable particle size range of 2–6 nm, underscores the robustness of our methodological approach. RDE analyses suggest that our synthesized catalysts outpace commercially accessible Pt/C variants of similar Pt wt %. However, when the data were transferred to MEA settings, notable deviations from RDE findings emerged, pinpointing the escalating role of mass transfer within the ORR framework. This observation found further resonance in our subsequent COMSOL simulations, underscoring the determinant role of mass transfer in MEA efficacy. This research paves the way for a more discerning approach to CL design, holding significant promise for the enhancement of future PEMFCs.