Complex causality behind low-Pt-loading cathode degradation in proton exchange membrane fuel cells

Substantial progress has been made towards lowering the cathodic Pt loading in proton exchange membrane fuel cells (PEMFCs). Nevertheless, the poor understanding of the degradation mechanisms of PEMFCs with low cathodic Pt loadings has been limiting the design of high-durability low-Pt catalyst layers (CLs). In this study, we investigated these degradation mechanisms under simulated dynamic automotive conditions using both in situ and physical characterisation techniques. Notably, the cell with the low-Pt-loading experienced significant Ostwald ripening, but Pt deposition on the membrane was negligible. Experimental data and model calculations confirmed that Pt dissolution was enhanced in the cell with the low-Pt-loading, where few dissolved Pt ions were deposited in the membrane, whereas the redeposition of Pt ions remaining in the CL on larger Pt particles exacerbated Ostwald ripening. Thus, the prolonged operation of PEMFCs with low-Pt-loading would require limiting the extent of Ostwald ripening in the CL. Pt dissolution and Ostwald ripening in cells with low-Pt-loading were found to be effectively mitigated by increasing the lower potential limit to within the range of 0.67–0.7 V. These new insights into degradation mechanisms and mitigation strategies are expected to inspire the development of new guidelines for the design of low-Pt electrodes.