Aplicação da teoria ac de eletrodos porosos na investigação da cinética de dispositivos eletrocatalíticos / Application of ac theory for porous electrode in the investigation in the kinetics of electrocatalytic devises

AUTOR(ES)
DATA DE PUBLICAÇÃO

2008

RESUMO

This work consists in using Electrochemical Impedance Spectroscopy (EIS) in the research of various electrocatalytic materials. The porous electrode model is a very promising approach to treat the frequency responses of Dimensionally Stable Anodes (DSA®). Once the application of the model is established, it is possible to obtain important kinetic information while various factors occurring in the system are analyzed. This allows confirmation results obtained by other techniques. Electrodes of the DSA® type with composition Ti/Ru 0,3Ti(0,7-x)SnxO2 (x=0; 0,3 e 0,7) were investigated. In order to compare the results obtained for DSA® Ti/Ru 0,3Ti0,7O2 electrodes by EIS (ac) with the kinetic studies by Tafel (dc) polarization curves performed in acid environment. Additionally, an investigation of the anodes, applicable to Direct Oxidation of Ethanol Fuel Cells (DEFCs), with composition Ti/Pt, Ti/Pt:Ru (80:20), Ti/Pt:Sn (80:20) and Ti/Pt:Ru:Sn (80:10:10) in acid environment and also in ethanol was carried out, using EIS as a diagnosis element for the activity of the anode composition. The EIS results confirmed that increasing concentration of SnO2 in the DSA® composition enhances oxygen formation, as reported in the literature, for other electrochemical techniques. The EIS technique revealed that the transmission line of one canal provided satisfactory data for its elements, in agreement with literature data. Pt addition to the DSA® Ti/Ru 0,3Ti0,7O2 improved the material efficiency, giving smaller resistance values for charge transfer. The resistance of the charge transfer (Rtc) lowered with increasing potential, in the direction of RDO. Analysing the potential values as a function of the Tafel polarization curves and EIS, it is possible to conclude that there is a relationship between the ac and dc behaviors of the system. In the studies of materials applicable to DEFCs it was confirmed that Sn improves the activity for ethanol oxidation. The composition Ti/Pt:Sn (80:20) led to the best results in EIS tests, revealing lower resistance values in the charge transfer, in agreement with results obtained in the study of fuel cells.

ASSUNTO(S)

impedance eletrocatalysis eletrocatálise ethanol etanol impedância

ACESSO AO ARTIGO

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