Fe Stabilization by Intermetallic L1-FePt and Pt Catalysis Enhancement in L1-FePt/Pt Nanoparticles for Efficient Oxygen Reduction Reaction in Fuel Cells.

We report in this article a detailed study on how to stabilize a first-row transition metal (M) in an intermetallic L1-MPt alloy nanoparticle (NP) structure and how to surround the L1-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-FePt/Pt with a 5 Å Pt shell. The presence of Fe in the alloy core induces the desired compression of the thin Pt shell, especially the two atomic layers of Pt shell, further improving the ORR catalysis. This leads to much enhanced Pt catalysis for ORR in 0.1 M HClO solution (at both room temperature and 60 °C) and in the membrane electrode assembly (MEA) at 80 °C. The L1-FePt/Pt catalyst has a mass activity of 0.7 A/mg from the half-cell ORR test and shows no obvious mass activity loss after 30 000 potential cycles between 0.6 and 0.95 V at 80 °C in the MEA, meeting the DOE 2020 target (<40% loss in mass activity). We are extending the concept and preparing other L1-MPt/Pt NPs, such as L1-CoPt/Pt NPs, with reduced NP size as a highly efficient ORR catalyst for automotive fuel cell applications.