Hard-Magnet L10-CoPt Nanoparticles Advance Fuel Cell Catalysis

Stabilizing transition metals (M) in MPt alloy under acidic conditions is challenging, yet crucial to boost Pt catalysis toward oxygen reduction reaction (ORR). We synthesized similar to 9 nm hard-magnet core/shell L1(0)-CoPt/Pt nanoparticles with 2-3 atomic layers of strained Pt shell for ORR. At 60 degrees C in acid, the hard-magnet L1(0)-CoPt better stabilizes Co (5% loss after 24 hr) than soft-magnet A1-CoPt (34% loss in 7 hr). L1(0)-CoPt/Pt achievesmass activities (MA) of 0.56 A/mg(Pt) initially and 0.45 A/mg(Pt) after 30,000 voltage cycles in the membrane electrode assembly at 80 degrees C, exceeding the DOE 2020 targets on Pt activity and durability (0.44 A/mg(Pt) in MA and < 40% loss in MA after 30,000 cycles). Density functional theory calculations suggest that the ligand effect of Co and the biaxial strain (-4.50%/-4.25%) of the Pt shell weaken the binding of oxygenated species, leading to enhanced ORR performance in fuel cells.