Effect of Platinum Shell Thickening on Dealloying of PtCu Octahedral Nanoparticles for Electrocatalytic Oxygen Reduction Reaction

Controlling the structural evolution of Pt-based bimetallic nanoparticles (NPs) is critical for enhancing their activity and durability as oxygen reduction reaction (ORR) electrocatalysts. In this study, we systematically investigated the influence of solvothermal synthesis duration on the morphology, composition, and performance of carbon-supported PtCu octahedral NPs. By varying the reaction time from 3 to 72 h, we observe time-dependent changes in particle shape, surface composition, and electrochemical behavior. Catalysts synthesized at 24 and 48 h exhibited the most favorable combination of morphology and surface composition, with well-defined octahedral shapes and Pt-rich shells. The 24 h sample reached a specific activity of 1.16 mA/cm2Pt and a mass activity of 1.17 A/mgPt (2.18 mA/cm2Pt, 1.00 A/mgPt after 10,000 accelerated degradation cycles), while the 48 h sample achieved 1.38 mA/cm2Pt and 1.15 A/mgPt, rising to 2.18 mA/cm2Pt and 1.23 A/mgPt after 10,000 cycles. Structural and spectroscopic characterizations, including X-ray absorption spectroscopy (XAS) and X-ray photoelectron spectroscopy (XPS), confirm the formation of a Pt-enriched surface and charge transfer from Cu to Pt; both effects contribute to improved stability and catalytic activity. These findings demonstrate that time-controlled solvothermal synthesis is a strategy for tuning the structure and electronic properties of the ORR electrocatalysts.