A reduced imidazolium cation layer serves as the active site for electrochemical carbon dioxide reduction

• Published in: Applied catalysis. B, Environmental Vol. 264; p. 118495
• Main Authors: Wang, Yuanqing, Hayashi, Toru, He, Daoping, Li, Yamei, Jin, Fangming, Nakamura, Ryuhei
• Format: Journal Article
• Language: English
• Published: Amsterdam Elsevier B.V 05.05.2020; Elsevier BV
• Subjects: Carbon dioxide; Cations; Chemical reduction; DFT calculation; Electrochemical carbon dioxide reduction; Electrochemistry; Electrodes; Hydrogen evolution; Ionic liquid; Ionic liquids; Ions; Mass spectrometry; Mass spectroscopy; Raman spectroscopy; Reduced imidazolium cation; Selectivity; DFT calculation; Electrochemical carbon dioxide reduction; Reduced imidazolium cation; Ionic liquid
• ISSN: 0926-3373; 1873-3883
• DOI: 10.1016/j.apcatb.2019.118495

[Display omitted] •A suppression of HER after the first cycle of CV was found in the presence of EMIM-BF4 on a copper electrode.•A reduced EMIM+ cation layer can prohibit HER and may initiate CO2 reduction.•DFT calculation showed that the reduction from aqueous EMIM+ cation to adsorbed EMIM radical on Cu(111) occurs at −0.7 V.•Interaction of organic molecule with electrode material is vital for CO2 activation. Since Rosen et al. in 2011 found that imidazolium ionic liquid significantly increases the activity and selectivity of the electrochemical reduction of CO2 to CO, the catalytic role of imidazolium ionic liquid in CO2 reduction has been intensively investigated. To date, however, the molecular mechanism behind this activity and selectivity remains to be elucidated. Here, we report the role of a reduced imidazolium cation layer in facilitating CO2 reduction on a Cu electrode surface while simultaneously suppressing hydrogen evolution. The results of cyclic voltammetry and on-line differential electrochemical mass spectrometry, coupled with in-situ surface-enhanced Raman spectroscopy, indicated that the Cu surface is partially covered by the reduced imidazolium cations at potentials around −0.8 V vs SHE. This potential is consistent well with the observed onset potential for the electroreduction of CO2, as well as the calculated one-electron reduction potential of imidazolium cations to form imidazolium radicals on Cu electrodes demonstrating that the reduced imidazolium species serves as the active site for CO2 reduction.