Composition effect of oxygen reduction reaction on PtSn nanorods: An experimental and computational study

In the development of emerging energy, proton exchange membrane fuel cells (PEMFCs) have been widely researched. Nevertheless, because of the high price and scarcity of Pt and its sluggish kinetics for oxygen reduction reaction (ORR), the preparation of highly effective cathode catalysts becomes one of the main challenges for PEMFCs in the practical application. In this study, carbon supported PtSn nanorods (NRs) with metal loading of 50 wt % and different Pt/Sn ratios of 80/20, 65/35 and 50/50 have been prepared by formic acid reduction method. The ORR performance of the catalysts can be promoted synergistically by one-dimensional (1-D) NRs and is varied with the Pt/Sn ratios. The experimental and computational efforts reveal that the Sn addition can lower the unoccupied d-band of neighboring Pt and the oxygen-containing species (OCS) on Sn can suppress their oxidation through the repulsion effect. Consequently, PtSn electrodes show the improved ORR activity; Pt₅₀Sn₅₀ with the highest Sn content results in the highest mass activity. On the other hand, the negatively charged OCS on Sn attracts the positively charged Pt and destructs the structures of PtSn NRs. Accordingly, Pt₈₀Sn₂₀ with the lowest Sn contain has the highest concentration of 1-D PtSn NRs and shows the best stability in the accelerated durability test (ADT). Our results clarify the mechanism of ORR on PtSn electrodes and suggest the importance of the precise control of atomic ratios on PtSn catalysts for the practical purpose. The findings open new perspectives about the origins of the activity and stability of the PtSn catalysts, especially for 1-D catalysts.