On the Mechanism of Carbon Dioxide Reduction on Sn-Based Electrodes: Insights into the Role of Oxide Surfaces

Autor(es)

Damas, Giane B. ^[1] ; Miranda, Caetano R. ^[2] ; Sgarbi, Ricardo ^[3] ; Portela, James M. ^[3] ; Camilo, Mariana R. ^[3] ; Lima, Fabio H. B. ^[3] ; Araujo, C. Moyses ^[1]

Afiliação do(s) autor(es)

^[1] Uppsala Univ, Dept Phys & Astron, Mat Theory Div, S-75120 Uppsala - Sweden

^[2] Univ Sao Paulo, Inst Phys, BR-05508090 Sao Paulo - Brazil

^[3] Univ Sao Paulo, Inst Chem, BR-13560970 Sao Carlos, SP - Brazil

• Tipo de documento: Artigo Científico
• Fonte: CATALYSTS; v. 9, n. 8 AUG 2019.
• Citações Web of Science: 0

Resumo

The electrochemical reduction of carbon dioxide into carbon monoxide, hydrocarbons and formic acid has offered an interesting alternative for a sustainable energy scenario. In this context, Sn-based electrodes have attracted a great deal of attention because they present low price and toxicity, as well as high faradaic efficiency (FE) for formic acid (or formate) production at relatively low overpotentials. In this work, we investigate the role of tin oxide surfaces on Sn-based electrodes for carbon dioxide reduction into formate by means of experimental and theoretical methods. Cyclic voltammetry measurements of Sn-based electrodes, with different initial degree of oxidation, result in similar onset potentials for the CO2 reduction to formate, ca. -0.8 to -0.9 V vs. reversible hydrogen electrode (RHE), with faradaic efficiencies of about 90-92% at -1.25 V (vs. RHE). These results indicate that under in-situ conditions, the electrode surfaces might converge to very similar structures, with partially reduced or metastable Sn oxides, which serve as active sites for the CO2 reduction. The high faradaic efficiencies of the Sn electrodes brought by the etching/air exposition procedure is ascribed to the formation of a Sn oxide layer with optimized thickness, which is persistent under in situ conditions. Such oxide layer enables the CO2 ``activation{''}, also favoring the electron transfer during the CO2 reduction reaction due to its better electric conductivity. In order to elucidate the reaction mechanism, we have performed density functional theory calculations on different slab models starting from the bulk SnO and Sn6O4(OH)(4) compounds with focus on the formation of -OH groups at the water-oxide interface. We have found that the insertion of CO2 into the Sn-OH bond is thermodynamically favorable, leading to the stabilization of the tin-carbonate species, which is subsequently reduced to produce formic acid through a proton-coupled electron transfer process. The calculated potential for CO2 reduction (E = -1.09 V vs. RHE) displays good agreement with the experimental findings and, therefore, support the CO2 insertion onto Sn-oxide as a plausible mechanism for the CO2 reduction in the potential domain where metastable oxides are still present on the Sn surface. These results not only rationalize a number of literature divergent reports but also provide a guideline for the design of efficient CO2 reduction electrocatalysts. (AU)

• Processo FAPESP: 14/26699-3 - Desenvolvimento de eletrocatalisadores para a eletrorredução de CO2 e foto-eletrooxidação da água: investigação dos produtos reacionais por espectrometria de massas on-line em fluxo
• Beneficiário: Mariana Romano Camilo Casale
• Modalidade de apoio: Bolsas no Brasil - Pós-Doutorado
• Processo FAPESP: 16/13323-0 - Eletroquímica do Dióxido de Carbono e da Água: Aplicação em Estocagem e Aproveitamento de Energia
• Beneficiário: Fabio Henrique Barros de Lima
• Modalidade de apoio: Auxílio à Pesquisa - Regular
• Processo FAPESP: 13/16930-7 - Eletrocatálise V: processos eletrocatalíticos de interconversão entre as energias química e elétrica
• Beneficiário: Edson Antonio Ticianelli
• Modalidade de apoio: Auxílio à Pesquisa - Temático
• Processo FAPESP: 17/02317-2 - Interfaces em materiais: propriedades eletrônicas, magnéticas, estruturais e de transporte
• Beneficiário: Adalberto Fazzio
• Modalidade de apoio: Auxílio à Pesquisa - Temático