Effect of Annealing Treatment on Electrocatalytic Properties of Copper Electrodes toward Enhanced CO2 Reduction

Author(s)

Lopes, Osmando F. ^[1] ; Varela, Hamilton ^[1]

Affiliation

^[1] Univ Sao Paulo, Inst Chem Sao Carlos, POB 780, BR-13560970 Sao Carlos, SP - Brazil

• Document type: Journal article
• Source: CHEMISTRYSELECT; v. 3, n. 31, p. 9046-9055, AUG 23 2018.
• Web of Science Citations: 2

Abstract

CO2 reduction (CO2RR) into added-value chemicals is a key contribution to solve energetic and environmental issues. The performance of Cu-based electrodes towards CO2RR is strongly affected by pretreatments and presence of impurities, such as copper oxides. We evaluated the effect of different treatments, electropolishing (Cu-p), and annealing treatments under oxidizing (Cu-Air) and reducing (Cu-H-2) conditions, on the performance of Cu electrodes designed for CO2RR. Characterizations revealed the presence of Cu2O and CuO layers on the surface of the Cu-Air electrode. All electrodes formed only HCOO- ions as liquid-phase products, with yield of 480 mg L-1 of HCOO- and Faradaic efficiency (FE) of 30% for the Cu-Air electrode and 25 mg L-1 with FE of 16%, and 26 mg L-1 with FE of 10% for the Cu-p and Cu-H-2 electrodes, respectively. Overall, the HCOO- concentration increased with an increasing KHCO3 concentration, while the FE increased up to 46%, due to insertion of CO2 into the electrical double layer, generating an intermediate specie prior to the electrochemical CO2RR. CO2RR tests performed on the Cu-Air and Cu-p electrodes under galvanostatic conditions showed HCOO- FE of 32% and 16%, respectively. Therefore, the increasing local pH mechanism does not play a key role in the liquid-phase products of CO2RR. The activity of the Cu-Air electrode for CO2RR remained stable over 64 hours. It was proposed that Cu1+ was the active site responsible for CO2RR. CO, C2H4, C2H6 and H-2 were formed by gas-phase electrochemical CO2RR using the Cu-Air electrode, with total FE higher than 65%. We have uncovered the role played by the type of pre-treatment in the performance of Cu-based electrodes on CO2RR and the reason for the increased electrocatalytic activity of oxidized Cu electrodes. (AU)

• FAPESP's process: 16/09746-3 - Electro-/Photoelectrocatalysis Reduction of CO2: Efficiency, Selectivity and Oscillatory Kinetics
• Grantee: Osmando Ferreira Lopes
• Support Opportunities: Scholarships in Brazil - Post-Doctoral
• FAPESP's process: 13/16930-7 - Electrocatalysis V: electrocatalytic processes of chemical and electrical energy interconversion
• Grantee: Edson Antonio Ticianelli
• Support Opportunities: Research Projects - Thematic Grants