Room-temperature synthesis of Pd cores and CO-assisted Pt monolayer growth for durable oxygen reduction reaction electrocatalysts

• Room-temperature polyol synthesis yields uniform 3–4 nm Pd nanoparticles. • Facile synthesis is scalable up to 5 g while maintaining uniform Pd dispersion. • CO-adsorption-induced deposition enables conformal Pt monolayer growth on Pd cores. • Pd@Pt/C exhibits a 2.9-fold higher ORR mass activity than commercial Pt/C. • Electrochemical tests confirm superior durability of Pd@Pt/C after AST 30 k cycles. Durable and cost-effective electrocatalysts are essential for advancing polymer electrolyte fuel cells (PEFCs) in next-generation energy systems. This study presents a facile room-temperature synthesis of uniformly dispersed Pd nanoparticles on carbon supports, followed by Pt monolayer (ML) deposition via a CO-adsorption-induced deposition (CO-AID) method to form Pd@Pt/C core–shell catalysts. Diethylene glycol (DEG) was identified as the optimal polyol solvent, enabling the direct synthesis of 3–4 nm Pd nanoparticles at room temperature, in contrast to the temperatures of over 160 °C typically required for polyol reduction. Structural characterization confirmed the successful formation of a Pt monolayer shell on Pd cores. Electrochemical measurements further revealed a mass activity of 0.649 m 2 g −1 Pt for the oxygen reduction reaction (ORR), representing a substantial improvement over the 0.226 m 2 g −1 Pt observed for commercial Pt/C. After accelerated stress test (AST) 30 k cycles, Pd@Pt/C retained its core–shell structure and exhibited only a minor mass activity loss of 6.5%, whereas Pt/C underwent severe degradation with a 41.2% loss. Single-cell evaluations further validated these findings, with Pd@Pt/C maintaining higher cell activity and superior long-term durability under PEFC operations. These results highlight the potential of Pd@Pt/C as a scalable and robust alternative to conventional Pt/C catalysts for practical PEFC applications.