The effects of power ultrasound (24 kHz) on the electrochemical reduction of CO2 on polycrystalline copper electrodes

Md Hujjatul Islam; Hamed Mehrabi; Robert H Coridan; Odne S Burheim; Jean-Yves Hihn; Bruno G Pollet

doi:10.1016/j.ultsonch.2020.105401

The effects of power ultrasound (24 kHz) on the electrochemical reduction of CO₂ on polycrystalline copper electrodes

Ultrason Sonochem. 2021 Apr:72:105401. doi: 10.1016/j.ultsonch.2020.105401. Epub 2020 Dec 3.

Authors

Md Hujjatul Islam¹, Hamed Mehrabi², Robert H Coridan³, Odne S Burheim⁴, Jean-Yves Hihn⁵, Bruno G Pollet⁴

Affiliations

¹ Hydrogen Energy and Sonochemistry Research Group, Department of Energy and Process Engineering, Norwegian University of Science and Technology (NTNU), Trondheim, Norway. Electronic address: md.h.islam@ntnu.no.
² Microelectronics-Photonics Program, University of Arkansas, Fayetteville, AR, USA.
³ Microelectronics-Photonics Program, University of Arkansas, Fayetteville, AR, USA; Department of Chemistry and Biochemistry, University of Arkansas, Fayetteville AR, USA.
⁴ Hydrogen Energy and Sonochemistry Research Group, Department of Energy and Process Engineering, Norwegian University of Science and Technology (NTNU), Trondheim, Norway.
⁵ Hydrogen Energy and Sonochemistry Research Group, Department of Energy and Process Engineering, Norwegian University of Science and Technology (NTNU), Trondheim, Norway; UTINAM UMR 6213 CNRS, Université Bourgogne Franche-Comté, Besançon, France.

Abstract

The electrochemical CO₂ reduction reaction (CO2RR) on polycrystalline copper (Cu) electrode was performed in a CO₂-saturated 0.10 M Na₂CO₃ aqueous solution at 278 K in the absence and presence of low-frequency high-power ultrasound (f = 24 kHz, P_T ~ 1.23 kW/dm³) in a specially and well-characterized sonoelectrochemical reactor. It was found that in the presence of ultrasound, the cathodic current (I_c) for CO₂ reduction increased significantly when compared to that in the absence of ultrasound (silent conditions). It was observed that ultrasound increased the faradaic efficiency of carbon monoxide (CO), methane (CH₄) and ethylene (C₂H₄) formation and decreased the faradaic efficiency of molecular hydrogen (H₂). Under ultrasonication, a ca. 40% increase in faradaic efficiency was obtained for methane formation through the CO2RR. In addition, and interestingly, water-soluble CO₂ reduction products such as formic acid and ethanol were found under ultrasonic conditions whereas under silent conditions, these expected electrochemical CO2RR products were absent. It was also found that power ultrasound increases the formation of smaller hydrocarbons through the CO2RR and may initiate new chemical reaction pathways through the sonolytic di-hydrogen splitting yielding other products, and simultaneously reducing the overall molecular hydrogen gas formation.

Keywords: CO(2) electrochemical reduction (CO2RR); Ethanol; Formic acid; Methane; Sonoelectrochemistry; hydrogen evolution reaction (HER).