Rhombohedral Ordered Intermetallic Nanocatalyst Boosts\nthe Oxygen Reduction Reaction

Abstract

Low\nplatinum-group-metal (PGM) ordered intermetallic catalysts\nhave been considered one of the most promising candidates for catalyzing\nthe oxygen reduction reaction (ORR) in fuel cells, but achieving the\ndesired performances in terms of activity, durability, and cost is\nstill a grand challenge for the fuel cell research field. While the\ncubic- and tetragonal-ordered (L1₂ and L1₀ phases)\nlow-PGM nanocatalysts have been investigated extensively and have\nshown considerably improved durability and activity toward the ORR,\nso far, little is known about rhombohedral ordered L1₁ catalysts.\nWe report the synthesis of an L1₁-ordered PtCu catalyst\nfor the ORR. We demonstrate that by applying nitrogen (N) doping through\na thermal treatment in an NH₃ gas, the activity and stability\nof the N-doped, rhombohedral ordered PtCu catalyst can be further\nenhanced, and the ORR mass and specific activities achieve nearly\n5-fold and 4-fold enhancement in acidic media, respectively, relative\nto those of commercial Pt/C. <i>In situ</i> synchrotron\nX-ray absorption and pair-distribution-function measurements reveal\nthat both the formation of the ordered intermetallic structure and\nN-doping synergistically improve the corrosion resistance of the PtCu\ncatalyst by lowering the Cu diffusivity and introduce a compressive\nstrain effect regulating the adsorption of oxygenated species on the\nPt surface, thus accounting for the improved ORR kinetics.