Sonochemical gram-scale synthesis of core–shell PdCo@Pt nanoparticle and investigation of post heat-treatment effect for various gas atmospheres

Abstract For the commercialization of polymer electrolyte fuel cells (PEFCs), the development of highly active and durable electrocatalysts is essential to improve the sluggish oxygen reduction reaction (ORR) and reduce the usage of precious group metals (Pt and Pd) in the catalyst layer of the membrane electrode assembly (MEA). Core–shell structured nanoparticles (NPs) have garnered significant attention because their unique structure enables the maximization of Pt utilization and catalytic performance. Moreover, ternary Pt-based core–shell electrocatalysts are being actively investigated for securing additional activity and durability in ORR. Herein, we report the sonochemical preparation of ternary PdCo@Pt NPs up to 10.0 g per batch and post-heat treatment effects based on the gas atmosphere. Based on the difference in reactivity of metal β-ketonate precursors under ultrasound irradiation, a core–shell structure with a Pt skin layer is formed and the as-prepared PdCo@Pt sample is post heat-treated under various gas atmospheres (N2, H2/N2, and NH3/N2) to compare the catalytic activity and durability of ORR. The structural characterization of the heat-treated PdCo@Pt samples reveals that the gas atmosphere during heat treatment controlls the particle size, the degree of alloying and the Pt shell thickness. In addition, electrochemical studies show that heat-treated PdCo@Pt samples under a reducing atmosphere (H2/N2, NH3/N2) exhibit higher ORR activity and better durability than those heat-treated under an inert atmosphere (N2). We demonstrated that the use of ultrasound enables mass production of core-shell NPs, and gas induced segregation under post heat-treatment help to control the structure of appropriate electrocatalyst for PEFCs.