Review of different methods for developing nanoelectrocatalysts for the oxidation of organic compounds

Comparative study of ethanol oxidation at Pt: Based nanoalloys and UPD modified Pt nanoparticles

The activity of two alloys, Pt3Sn/C and Pt3Ru2/C, was compared with the activity of Pt/C modified with corresponding amounts of SnUPD (?25 %) and RuUPD (?40 %) in oxidation of ethanol. Pt3Sn/C, Pt3Ru2/C and Pt/C catalysts were characterized by XRD. To establish the activity and stability of the catalysts, potentiodynamic, quasi steady-state and chronoamperometric measurements were performed. Both alloys are more active than SnUPD or RuUPD modified Pt/C catalysts. Electronic effect determining dominantly the activity of Pt3Sn/C is the main reason for its higher activity compared to Pt3Ru2/C. Since SnUPD and RuUPD do not provoke any significant modification of electronic environment, both modified Pt/C catalysts are less active than corresponding alloys. More pronounced difference in activity between Pt3Sn/C and SnUPD modified Pt/C than between Pt3Ru2/C and RuUPD modified Pt/C is caused by electronic effect in Pt3Sn/C. High activity of Pt3Sn/C modified with small amount of SnUPD (?10%) can be explained by combining the electronic effect, causing less strongly bonded adsorbate on Pt sites and easier mobility of SnUPD, with enhanced amount of oxygen-containing species on Sn sites resulting finally in reinforcement of bifunctional mechanism.

Improvement of the platinum nanoparticles-carbon substrate interaction by insertion of a thiophenol molecular bridge

The effect of thiophenol layer grafted on carbon for platinum catalyst stabilization was studied. The grafted layer was prepared by reduction of 4-thiophenoldiazonium ions in the presence of Vulcan XC72 substrate. The grafted layer was characterized by elemental analysis, thermogravimetric analysis coupled with mass spectrometry, and X-ray photoelectron spectroscopy. Platinum nanoparticles prepared by the "water in oil" microemulsion method were then deposited on modified substrates and bare Vulcan XC72. The platinum stability improvement was characterized by in situ X-ray diffraction and electrochemical aging. These experiments enabled to evidence a lower crystallite growth during heat treatment under hydrogen atmosphere and a lower active surface area loss for platinum particles deposited on modified substrates compared to those deposited on bare Vulcan XC72. This stability improvement can be attributed to a better interaction between platinum particles and carbon substrate due to the thiophenol molecular bridge.

Effect of reduction temperature on the preparation and characterization of Pt-Ru nanoparticles on multiwalled carbon nanotubes

Carbon nanotubes (CNT) supported platinum-ruthenium (Pt-Ru) catalysts were prepared by impregnation-reduction using an ethanolic solution of H2PtCl6 and RuCl3. The effect of reduction temperatures on particle size, surface area and their relationship to the electrocatalytic activity for methanol oxidation were investigated. Thermogravimetric analysis, scanning electron microscopy, transmission electron microscopy, X-ray diffraction (XRD) as well as X-ray photoelectron spectroscopy (XPS) were used for the catalyst characterization. XRD analysis showed that the PtRu/ CNT catalysts possibly consist of separate Pt and Ru phases. XPS analysis showed that the catalysts contain hydrous ruthenium oxide in addition to Pt and Ru metal and oxide species. The electrocatalytic activities of the catalysts were investigated in half-cell experiments using cyclic voltammetry, CO stripping voltammetry, chronoamperometry, and impedance spectroscopy. The results showed that the catalyst reduced at a temperature of 350 degrees C had the largest electrochemical surface area, lowest charge transfer resistance and the highest electrocatalytic activity for methanol oxidation. The superior catalytic activity is discussed based on the presence of appropriate amount of hydrated Ru oxide.