Gold/Platinum nanosponges for electrocatalytic oxidation of methanol

Abstract

We have prepared Au_n/Pt nanosponges that are highly electroactive for the oxidation of MeOH, from Pt nanosponges and AuCl₄⁻ ions through galvanic reactions at ambient temperature and pressure. At AuCl₄⁻ concentrations of 0, 0.1, 0.3, 0.5, 1.0, and 2.0 mM and a constant content of Pt nanosponges, we obtained Au_n/Pt nanosponges having values of n of 0, 0.1, 0.2, 0.3, 0.5, and 0.8, respectively. The average size of the Au nanoparticles deposited on the surfaces of the Pt nanosponges increased upon increasing the AuCl₄⁻ concentration (at a constant Pt nanosponge content). We used UV–Vis absorption spectroscopy, energy dispersive X-ray spectroscopy, X-ray diffraction, inductively coupled plasma mass spectrometry, and transmission electron microscopy to characterize the as-prepared Au_n/Pt nanosponges. These techniques revealed that the Au_n/Pt nanosponges comprised spherical Au nanoparticles (diameter: 6–17 nm) and assemblies of Pt nanorods (width: 3 nm; length: 17 nm). Cyclic voltammetry indicated that the electrocatalytic oxidation of MeOH was dependent on the content of Au nanoparticles on the surfaces of the Pt nanosponges. The Au_0.5/Pt nanosponges provided the highest electrocatalytic efficiency—indeed, it was superior to those of commercial Pt nanoparticles and other previously reported Pt nanosponges. The Au_0.5/Pt nanosponges exhibited a mass activity of 231 mA mg⁻¹ and a forward-to-reverse anodic peak current ratio of 2.2—i.e., excellent electrocatalytic activity for the oxidation of MeOH.