Shell-Thickness-Controlled Synthesis of Core-Shell Pd@Pt Nanocubes and Tuning of Their Oxygen Reduction Activities

Abstract

An approach to control Pt shell thickness in the synthesis of Pd@Pt core-shell nanocubes (NCs) has been successfully developed. Tuning the Pt and Pd precursor concentration ratio (Pt4+/Pd2+) in the reaction mixture allowed precise control over the Pt shell thickness in the range of 0.3–4.9 nm. At low Pt4+/Pd2+ ratios (≤1/4), the deposition of Pt occurred via a layer-by-layer mode, whereas layer-by-layer deposition followed by Pt island growth was possible at higher Pt4+/Pd2+ ratios (1/3, 1/2, and 1). Additionally, rotating ring-disk electrode experiments determined the shell-thickness-dependent specific activities (SAs) and mass activities (MAs) of these Pd@Pt NCs, which acted as oxygen reduction catalysts in NaOH solution. Among these core-shell catalysts, the Pd1@Pt1/6 NCs (0.3 nm Pt shell) displayed the highest SA (0.4398 mA cm–2) and MA (2.915 mA μg–1) values, which were 3.38 and 2.53 times higher than the corresponding values for Pt nanoparticles (SA = 0.13 mA cm–2, MA = 1.15 mA μg–1). These results, supported by X ray photoelectron spectroscopy observations, indicate that the high activity of Pd1@Pt1/6 NCs is due to the modified electronic properties of the Pt shell influenced by the Pd NC core.