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  1. 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 ~9 nm hard-magnet core/shell L1 0-CoPt/Pt nanoparticles with 2–3 atomic layers of strained Pt shell for ORR. At 60°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 achieves mass 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°C, exceeding the DOE 2020 targets on Pt activitymore » and durability (0.44 A/mg Pt in MA and <40% loss in MA after 30,000 cycles). Lastly, 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.« less
  2. We report in this article a detailed study on how to stabilize a first-row transition metal (M) in an intermetallic L1 0-MPt alloy nanoparticle (NP) structure and how to surround the L1 0-MPt with an atomic layer of Pt to enhance the electrocatalysis of Pt for oxygen reduction reaction (ORR) in fuel cell operation conditions. Using 8 nm FePt NPs as an example, we demonstrate that Fe can be stabilized more efficiently in a core/shell structured L1 0-FePt/Pt with a 5 Å Pt shell. The presence of Fe in the alloy core induces the desired compression of the thin Ptmore » shell, especially the 2 atomic layers of Pt shell, further improving the ORR catalysis. This leads to much enhanced Pt catalysis for ORR in 0.1 M HClO 4 solution (both at room temperature and 60°C) and in the membrane electrode assembly (MEA) at 80°C. The L1 0-FePt/Pt catalyst has a mass activity of 0.7 A/mg Pt from the half-cell ORR test and shows no obvious mass activity loss after 30,000 potential cycles between 0.6 V and 0.95 V at 80°C in the MEA, meeting the DOE 2020 target (<40% loss in mass activity). Here, we are extending the concept and preparing other L1 0-MPt/Pt NPs, such as L1 0-CoPt/Pt NPs, with reduced NP size as a highly efficient ORR catalyst for automotive fuel cell applications.« less
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