Fundamental study of the ethanol electro-oxidation reaction on platinum single-crystal electrodes

Author(s)

Amaury Franklin Benvindo Barbosa

• Document type: Doctoral Thesis
• Press: São Carlos.
• Institution: Universidade de São Paulo (USP). Instituto de Química de São Carlos (IQSC/BT)
• Defense date: 2022-08-17

Examining board members

Germano Tremiliosi Filho; Flávio Colmati Junior; Pablo Sebastián Fernández; Janaina de Souza Garcia; Ana Maria Gomez Marin

• Advisor: Germano Tremiliosi Filho

Abstract

Direct ethanol fuel cells present some limitations due to the difficulty of achieving the complete oxidation of ethanol to carbon dioxide. To control the selectivity of this reaction, it is of crucial importance to understand how the electrocatalyst affects the various pathways on a molecular level. This thesis presents important insights of how the mechanism of the ethanol electro-oxidation reaction is influenced by the atomic superficial arrangement of a series of platinum single crystal electrodes and by the Sn ad-atoms deposited over such surface. Initially, the ethanol electro-oxidation was investigated in acid media on a series of well-ordered and disordered Pt(111) single crystal electrodes. Electrochemical results showed that the ethanol electro-oxidation is strongly affected by the -defect sites electrogenerated on Pt(111) electrodes. It was found that as the density of -defect sites increases, the ethanol electro-oxidation reaction is catalyzed better. In situ FTIR results demonstrated that the main products of the ethanol oxidation are CO2, acetaldehyde and acetic acid for all surfaces investigated. Additionally, adsorbed COlinear is observed. Next, the ethanol electro-oxidation was investigated in acid media on a series of Sn-modified and disordered Pt(111) single crystal electrodes. Voltammetric results of the ethanol electro-oxidation demonstrate that the partial decoration of -defect sites by Sn ad-atoms leads to a considerable increase in the catalytic activity towards ethanol electrooxidation reaction, when compared to the well-ordered Pt(111) surface and disordered Pt(111) surface without Sn. In situ FTIR results demonstrate that the main products of the ethanol oxidation are CO2, acetaldehyde and acetic acid for all surfaces investigated and the main effect of Sn is reflected in the increased production of acetic acid. Finally, acetaldehyde oxidation, an important intermediate of the ethanol oxidation, it was investigated on well-ordered Pt(111) and disordered Pt(111) surfaces, both modified by deposited Sn ad-atoms. Well-ordered Pt(111) is more active than stepped Pt(554) or disordered Pt(111) surfaces for acetaldehyde oxidation. However, the results were significantly improved and pointed out an outstanding performance when Pt(111) and disordered Pt(111) surfaces were modified by Sn. For both modified surfaces, there is an extraordinary displacement of the onset potential for more negative potentials, indicating oxidation of adsorbed species such as CO and CHx, already formed at low potentials. These results provide fundamental information on the ethanol oxidation reaction, which contributes to the atomic-level understanding of real catalysts. (AU)

• FAPESP's process: 16/13100-1 - Studies of ethanol and glycerol electro-oxidation reactions on surface modified platinum and gold single crystals
• Grantee: Amaury Franklin Benvindo Barbosa
• Support Opportunities: Scholarships in Brazil - Doctorate