\Dependence of the selectivity of the methanol and ethanol electrooxidation reaction on Pt/C and PtRh/C nanoparticles\

Author(s)

Kleber Bergamaski

• Document type: Doctoral Thesis
• Press: São Carlos.
• Institution: Universidade de São Paulo (USP). Instituto de Química de São Carlos (IQSC/BT)
• Defense date: 2005-12-22

Examining board members

Francisco Carlos Nart; Romeu Cardozo Rocha Filho; Lucia Helena Mascaro Sales; Estevam Vitorio Spinacé; Teresa Benita Iwasita de Vielstich

• Advisor: Francisco Carlos Nart

Abstract

The methanol and ethanol electrooxidation is a subject of intense studies in electrocatalysis. The aim of such attention concerning this alcohol electrooxidation activity is due to development of new energy converter systems more efficient and less pollutant. The electrocatalysis research has been also directed to nanoparticle systems. Metallic particles in nanometric size offer interesting aspects for structural effects studies in supported electrocatalysts. The particle size decrease could promote efficient catalyst use, once the ratio number of superficial atoms/total atoms raises. In this work, the electrochemical oxidation of methanol and ethanol on Pt/C and PtRh/C catalysts through differential electrochemical mass spectrometry (DEMS) was investigated. The atomic composition effect in the alcohol oxidation was studied on PtRh/C catalysts. The particle size effect on methanol oxidation reaction was studied on Pt/C E-Tek catalysts. It has been observed in this bimetallic catalysts that the higher rhodium content, the lower faradaic current. On the other hand, the efficiency for complete methanol electrooxidation to CO2 increased with rhodium addition in the platinum catalyst. To these results were assigned that electronic effect plays a key role in the mechanism of alcohol oxidation on bimetallic catalysts. For Pt/C E-Tek catalysts ones, the particle size effect in the methanol oxidation reaction was more evident. Methanol electrooxidation measurements have shown a high efficiency for complete alcohol oxidation to CO2 on the 30 and 40 % wt. Pt/C catalysts. It was inferred, in this case, that must be consider not only the particle morphology but also the coupling between different size particles via soluble products in order to improve a better understanding of global reaction mechanism. It was suggested that there is an optimum particle size range for efficient methanol electrooxidation to CO2, that is, 3 to 10 nm range. The loss of efficiency could be due to very small particles or very great particles resulting in methanol partial oxidation mainly to formaldehyde. (AU)