Lowering Pt loading in the cathode catalyst layer (CCL) is essential for the large-scale market penetration of proton exchange membrane fuel cells (PEMFCs). However, previous studies seemingly have suggested substantial decrease of catalytic capability in low-Pt electrodes due to the increased local oxygen transport resistance (Rlocal). Considering the benefits of shortened transport paths of gas, proton, and water, lowering the Pt loading would be double-edged for the output performance. Aiming at understanding the effects of Pt loading on the transport kinetics and catalyst effectiveness in CCL, the electrochemical behaviors of variously Pt-loaded PEMFC electrodes are investigated via detailed experimental characterizations, model analysis and numerical simulations. The results show that the Rlocal values corresponding to per mass of Pt actually decrease at low-Pt electrodes due to enhanced contribution of CCL|PEM interface to electrochemical surface area, which, together with the reduced transport paths of gas, proton, and water in thickness direction, result in much enhanced Pt effectiveness. The results also indicate that the molecular diffusion resistances in the macropores of CCL in low-Pt electrodes are negligibly smaller than that in the gas diffusion layer and Rlocal. These new insights into the loading effects would inspire new guidelines for low-Pt electrode design.

https://doi.org/10.1016/j.jpowsour.2023.232966