Structurally Ordered Low-Pt Intermetallic Electrocatalysts toward Durably High Oxygen Reduction Reaction Activity

Carbon-supported low-Pt ordered intermetallic nanoparticulate catalysts (PtM3, M = Fe, Co, and Ni) are explored in order to enhance the oxygen reduction reaction (ORR) activity while achieving a high stability compared to previously reported Pt-richer ordered intermetallics (Pt3M and PtM) and low-Pt disordered alloy catalysts. Upon high-temperature thermal annealing, ordered PtCo3 intermetallic nanoparticles are successfully prepared with minimum particle sintering. In contrast, the PtFe3 catalyst, despite the formation of ordered structure, suffers from obvious particle sintering and detrimental metal-support interaction, while the PtNi3 catalyst shows no structural ordering transition at all but significant particle sintering. The ordered PtCo3 catalyst exhibits durably thin Pt shells with a uniform thickness below 0.6 nm (corresponding to 2-3 Pt atomic layers) and a high Co content inside the nanoparticles after 10 000 potential cycling, leading to a durably compressive Pt surface and thereby both high activity (fivefold vs a commercial Pt catalyst and 1.7-fold vs an ordered PtCo intermetallic catalyst) and high durability (5 mV loss in half-wave potential and 9% drop in mass activity). These results provide a new strategy toward highly active and durable ORR electrocatalysts by rational development of low-Pt ordered intermetallics.