Fe Stabilization by Intermetallic L1₀-FePt and Pt Catalysis Enhancement in L1₀-FePt/Pt Nanoparticles for Efficient Oxygen Reduction Reaction in Fuel Cells

Abstract

We report in this article a detailed study on how to stabilize a first-row transition metal (M) in an intermetallic L1₀-MPt alloy nanoparticle (NP) structure and how to surround the L1₀-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 L1₀-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 HClO₄ solution (at both room temperature and 60 °C) and in the membrane electrode assembly (MEA) at 80 °C. The L1₀-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 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 L1₀-MPt/Pt NPs, such as L1₀-CoPt/Pt NPs, with reduced NP size as a highly efficient ORR catalyst for automotive fuel cell applications.