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| Author(s): |
Eduardo Gonçalves Ciapina
Total Authors: 1
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| Document type: | Master's Dissertation |
| Press: | São Carlos. |
| Institution: | Universidade de São Paulo (USP). Instituto de Química de São Carlos (IQSC/BT) |
| Defense date: | 2006-02-16 |
| Examining board members: |
Ernesto Rafael Gonzalez;
Assis Vicente Benedetti;
Fritz Cavalcante Huguenin
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| Advisor: | Ernesto Rafael Gonzalez |
| Abstract | |
In this work, kinetic aspects of CO electro-oxidation on Pt/C, Pt75Sn25/C and Pt65Ru35/C prepared by chemical reduction with formic acid were studied by Electrochemical Impedance Spectroscopy (EIS). The bulk composition of the asprepared PtSn/C and PtRu/C bimetallic materials, analyzed by EDX, was 77:23 and 64:36, respectively. Using high intensity XDR measurements the bulk structure and phase determinations could be established. The analysis of the XRD profiles of Pt75Sn25/C revealed partial alloy formation and the presence of a SnO2 phase. For Pt65Ru35/C, no alloy formation was verified. Potentiodynamic oxidation of CO in a CO-saturated solution compared with CO stripping voltammetry pointed out the presence of competitive adsorption between CO and oxygen containing species on the surface of Pt/C and Pt65Ru35/C while for Pt75Sn25/C no competition for surface sites was verified. Impedance measurements were conducted in two different conditions: i) in the absence of CO in solution and ii) in a CO saturated solution. Provided by an equivalent circuit the charge transfer resistance (Rct), was obtained for the studied materials. The mean double layer capacitance (Cdl) was also estimated from circuit parameters and revealed its dependence on the carbon monoxide surface coverage (_CO). Furthermore, the relation between the _CO and the charge transfer resistance for the reaction is discussed. Using EIS it was demonstrated that the Rct for the carbon monoxide electro-oxidation reaction on Pt75Sn25/C is much lower than on Pt/C and Pt65Ru35/C, which was related to the presence of oxygen-containing species already present in the SnO2 phase as well as to the faster adsorption processes on this material compared to Pt/C and Pt65Ru35/C. (AU) | |