Enhanced Electrocatalytic Oxidation of Small Organic Molecules on Platinum-Gold Nanowires: Influence of the Surface Structure and Pt-Pt/Pt-Au Pair Site Density.

The electrochemical oxidation of small organic molecules (SOMs) such as methanol and glucose is a critical process and has relevant applications in fuel cells and sensors. A key challenge in SOM oxidation is the poisoning of the surface by carbon monoxide (CO) and other partially oxidized intermediates, which is attributed to the presence of Pt-Pt pair sites. A promising pathway for overcoming this challenge is to develop catalysts that selectively oxidize SOMs via "direct" pathways that do not form CO as a primary intermediate. In this report, we utilize an ambient, template-based approach to prepare PtAu alloy nanowires with tunable compositions. X-ray photoelectron spectroscopy measurements reveal that the surface composition matches that of the bulk composition after synthesis. Monte Carlo method simulations of the surface structure of PtAu alloys with varying coverage of oxygen adsorbates and varying degrees of oxygen adsorption strength reveal that oxygen adsorption under electrochemical conditions enriches the surface with Pt and a large fraction of Pt-Pt sites remain on the surface even with the Au content of up to 50%. Electrochemical properties and the catalytic performance measurements of the PtAu nanowires for the oxidation of methanol and glucose reveal that the mechanistic pathways that produce CO are suppressed by the addition of relatively small quantities of Au (∼10%), and CO formation can be completely suppressed by 50% Au. The suppression of CO formation with small quantities of Au suggests that the presence of Pt-Au pair sites may be more important in determining the mechanism of SOM oxidation rather than Pt-Pt pair site density.

Sol-Gel Synthesis of Ruthenium Oxide Nanowires To Enhance Methanol Oxidation in Supported Platinum Nanoparticle Catalysts.

A template-directed, sol-gel synthesis is utilized to produce crystalline RuO2 nanowires. Crystalline nanowires with a diameter of 128 ± 15 nm were synthesized after treating the nanowires at 600 °C in air. Analysis of these nanowires by X-ray powder diffraction revealed the major crystalline phase to be tetragonal RuO2 with a small quantity of metallic ruthenium present. Further analysis of the nanowire structures by high-resolution transmission electron microscopy reveals that they are polycrystalline and are composed of interconnected, highly crystalline, nanoparticles having an average size of ∼25 nm. Uniform 3 nm Pt nanoparticles were dispersed on the surface of RuO2 nanowires using an ambient, solution-based technique yielding a hybrid catalyst for methanol oxidation. Linear sweep voltammograms (LSVs) and chronoamperometry performed in the presence of methanol in an acidic electrolyte revealed a significant enhancement in the onset potential, mass activity, and long-term stability compared with analogous Pt nanoparticles supported on commercially available Vulcan XC-72R carbon nanoparticles. Formic acid oxidation LSVs and CO stripping voltammetry revealed that the RuO2-supported Pt nanoparticles exhibit significantly higher CO tolerance, which leads to higher catalytic stability over a period of several hours. X-ray photoelectron spectroscopy results suggest that crystalline RuO2 leads to less-significant oxidation of the Pt surface relative to more widely studied hydrous RuO2 supports, thereby increasing catalytic performance.