| dc.description.abstract | The direct alcohol fuel cells have been studied extensively because of their stationary, mobile and portable applications. Ethanol is an attractive alternative fuel, because it is less toxic than methanol and can be produced in large quantities from agricultural products or biomass. However, the application of ethanol as fuels also exists some challenges, for example, ethanol is more difficult to be oxidized to CO2 and H2O than methanol owing to the difficulties in C–C bond breaking and the formation of CO-intermediates poison the Pt active sites. Therefore, in order to promote the electroactivity of the Pt-based catalysts toward ethanol oxidation reaction (EOR), the addition of some modifiers and the formation of the oxygen containing species have been elucidated as practical methods.
In this study, PtRu/SnxC (x = 0 - 20 wt %) electrocatalysts are prepared by the deposition-precipitation (DP) method using H2 as the reducing agent and Sn as the modifier for the EOR. Besides, the oxidation treatment is applied to generate the oxygen-containing species of the catalysts. The composition, structure, and surface-activity relationship of the Sn modified PtRu/C catalysts can be investigated systematically by the thermal gravimetric analysis (TGA), inductively coupled plasma-atomic emission spectrometer (ICP-AES), energy dispersive spectrometer (EDS), X-ray diffraction (XRD), high resolution transmission electron microscope (HRTEM), temperature-programmed reduction (TPR), X-ray photoelectron spectroscopy (XPS) measurements, and cyclic voltammetry (CV) measurements, respectively. For the as-reduced PtSn/C or PtRu/SnxC catalysts, it is observed that, some Sn exist as the metallic state and alloy with Pt to form Pt-Sn phase, and excess Sn exist as the amorphous SnO or crystalline SnO2. Those amorphous SnO instead of the crystalline SnO2 and the surface Ru on the Snx samples are beneficial for the EOR. During the O2-treatment, Ru and/or Sn diffuse out from the Pt-based alloy phase and exist as RuO2, SnO2 and/or Pt3Sn, respectively. These species can not only promote dissociative adsorption of ethanol on Pt surface but remove CO and carboxyl groups adsorbed on the adjacent Pt active sites. However, the excess oxides may block the active sites on the electrocatalyst surface and deteriorate the EOR or CO-oxidation reaction. Consequently, the surface composing of amorphous SnO and appreciate Ru species are significant condition of PtRn/SnxC toward EOR and CO-oxidation, thus the as-reduced PtRu/Sn10C electrocatalyst has the best EOR activity and CO-oxidation reaction among all samples. In terms of oxidized catalysts, PtRu/C containing RuO2 phase displays high EOR activity.
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