Synthesis of Pt@TiO2 nanocomposite electrocatalysts for enhanced methanol oxidation by hydrophobic nanoreactor templating

Abstract

In this work Pt@TiO₂ nanocomposite electrocatalysts for methanol oxidation were synthesized using a one-pot process by hydrophobic nanoreactor templating. TiO₂ was used as a support material for the platinum nanoparticles, thereby providing strong metal–support interactions. The Pt@TiO₂ electrocatalyst consists of a monolayer of spherical superstructures comprising finely dispersed platinum nanoparticles in a crystalline TiO₂ matrix as revealed by high resolution (scanning) transmission electron microscopy (HR-TEM and HR-STEM) combined with energy dispersive X-ray spectroscopy (EDX), electron diffraction and X-ray photoelectron spectroscopy (XPS). The Pt@TiO₂ electrocatalyst showed high methanol oxidation activity, exceeding the activity of a commercial Pt/C catalyst by a factor of 2.5, as well as a cathodically shifted methanol oxidation peak. The increased methanol oxidation activity of Pt@TiO₂ was attributed to its enhanced CO oxidation ability, an undesired intermediate, which is formed during methanol oxidation and poisons the Pt-surface. Indeed, CO stripping experiments confirmed that CO oxidation takes place at lower potentials in the case of Pt@TiO₂, leading to a cathodic shift of the CO oxidation peak by 100 mV compared to a commercial Pt/C reference catalyst. Insights into the mechanism of methanol oxidation on Pt@TiO₂ were found by comparison of methanol oxidation in different electrolytes. It was found that methanol oxidation via the CO-route is more pronounced on Pt@TiO₂ than on Pt/C. The improved activity for CO oxidation resulted thereby in a better catalyst performance, especially at low potentials, and an increased stability, as demonstrated by chronoamperometry. The long-term stability of the catalyst was further addressed by accelerated stress tests (AST), which showed that the superior catalytic activity is retained even after 30 000 potential cycles.