Ternary core-shell PdM@Pt (M = Mn and Fe) nanoparticle electrocatalysts with enhanced ORR catalytic properties

In this work, we introduce composition-tunable core-shell-like PdM@Pt (M = Mn and Fe) nanoparticles (NPs) on carbon support (PdM@Pt/C) synthesized by one-pot sonochemical reactions using high-intensity ultrasonic probe (150 W, 20 kHz, with 13 mm solid probe) and investigate their electrocatalytic performance for oxygen reduction reaction (ORR). The core-shell-like structure of the NPs are evidenced by the elemental distribution maps obtained by energy dispersive X-ray spectroscopy equipped on scanning transmission electron microscopy. Based on the characterization data, PdM@Pt NPs were synthesized with variable elemental compositions (Pd₄₉Fe₂₁@Pt₃₀, Pd₁₇Fe₃₁@Pt₅₂, Pd₄₆Mn₆@Pt₄₈ and Pd₁₅Mn₅@Pt₈₀). All PdM@Pt samples are composed of large (~10 nm) and small (~3 nm) NPs, the large ones appear to be aggregates of the smaller ones, and the proportion of the larger NPs increases with the Pd content, which can be explained with the known mechanisms of sonochemical reactions of related systems. Electrochemical analyses on samples show that the ORR mass activity of PdM@Pt/C is 3-fold (normalized by Pt) and 1.7-fold (normalized by platinum group metal (PGM)) higher than those of Pt/C (commercial). All PdM@Pt/C sample show superior durability with the electrochemical surface area (ECSA) change of -4.4-+12.0% and half-wave potential change (ΔE_1/2) of 8-14 mV after 10 k cycles accelerated stress test (AST) to Pt/C with ECSA change of -25.6% and ΔE_1/2 of 19 mV.