RESUMO
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.
RESUMO
Highly selective electrooxidation catalysts were synthesized by functionalizing a commercially available reference electrooxidation catalyst (Pt/Vulcan XC 72R) with a coating of the highly hydrophobic porous zeolitic imidazolate framework ZIF-8, an adsorbent with high affinity for the extraction of aliphatic alcohols from water. According to cyclovoltammetric studies in alkaline media at 25 °C, the ZIF-8 functionalized catalyst shows a high selectivity for the electrooxidation of small alcohols such as ethanol and methanol over more hydrophobic alcohols ( n-butanol, n-propanol). In contrast, the noncoated reference catalyst (Pt/Vulcan XC 72R) oxidizes all investigated alcohols with comparable current densities. Tafel curves confirm these observations and indicate a limited conversion of long chain alcohols, especially n-butanol, caused by the high affinity of the ZIF-8 for this molecule resulting in significant diffusion limitations.
RESUMO
In the present paper, we demonstrate a versatile approach for the one-pot synthesis of metal oxide yolk@shell nanostructures filled with bimetallic nanocores. This novel approach is based on the principles of hydrophobic nanoreactor soft-templating and is exemplified for the synthesis of various AgAuNP@tin-rich ITO (AgAu@ITOTR) yolk@shell nanomaterials. Hydrophobic nanoreactor soft-templating thereby takes advantage of polystyrene-block-poly(4-vinylpiridine) inverse micelles as two-compartment nanoreactor template, in which the core and the shell of the micelles serve as metal and metal oxide precursor reservoir, respectively. The composition, size and number of AuAg bimetallic nanoparticles incorporated within the ITOTR yolk@shell can easily be tuned. The conductivity of the ITOTR shell and the bimetallic composition of the AuAg nanoparticles, the as-synthesized AuAgNP@ITOTR yolk@shell materials could be used as efficient electrocatalysts for electrochemical glucose oxidation with improved onset potential when compared to their gold counterpart.