CO₂ Reduction Promoted by Imidazole Supported on a Phosphonium-Type Ionic-Liquid-Modified Au Electrode at a Low Overpotential

Abstract

The catalytic conversion of CO 2 to useful compounds is of great importance from the viewpoint of global warming and development of alternatives to fossil fuels. Electrochemical reduction of CO 2 using aromatic Nheterocylic molecules is a promising research area. We describe a high performance electrochemical system for reducing CO 2 to formate, methanol, and CO using imidazole incorporated into a phosphonium-type ionic liquid-modified Au electrode, imidazole@IL/Au, at a low onset-potential of −0.32 V versus Ag/AgCl. This represents a significant improvement relative to the onset-potential obtained using a conventional Au electrode (−0.56 V). In the reduction carried out at −0.4 V, formate is mainly generated and methanol and CO are also generated with high efficiency at −0.6 ∼ −0.8 V. The generation of methanol is confirmed by experiments using 13 CO 2 to generate 13 CH 3 OH. To understand the reaction behavior of CO 2 reduction, we characterized the reactions by conducting potential-and time-dependent in situ attenuated total reflection surface-enhanced infrared absorption spectroscopy (SEIRAS) measurements in D 2 O. During electrochemical CO 2 reduction at −0.8 V, the C−O stretching band for CDOD (or COD) increases and the CO stretching band for COOD increases at −0.4 V. These findings indicate that CO 2 reduction intermediates, CDOD (or COD) and COOD, are formed, depending on the reduction potential, to convert CO 2 to methanol and formate, respectively.

Electrochemical Reduction of CO2 over Heterogeneous Catalysts in Aqueous Solution: Recent Progress and Perspectives

“…The *CHO species in this pathway is an inevitable intermediate for further reduction into methanol, ethanol, ethylene and propanol . This also explains the coexistence of formate and methanol produced on some electrodes …”

Structure‐Sensitivity and Electrolyte Effects in CO2 Electroreduction: From Model Studies to Applications

“…They observed that, under the presence of the RTIL, the overpotential for the production of CO was around 0.170 V, lower than in Au substrates in aqueous solution, obtaining a 96 % of faradic efficiency of CO. The lower CO evolution overpotential was attributed to the stabilisation of the anion radical (CO 2 − ) by complexation with the cation in the RTIL medium, i. e., RTILs act as co‐catalyst of the CO 2 RR (Figure ) . However, the co‐catalytic property of RTILs is still poorly understood, and may involve a change of the catalytic properties of the modified electrified interface apart from complex intermediate stabilisation …”

“…The lower CO evolution overpotential was attributed to the stabilisation of the anion radical (CO 2 À ) by complexation with the cation in the RTIL medium, i. e., RTILs act as co-catalyst of the CO 2 RR (Figure 9). [153,154] However, the cocatalytic property of RTILs is still poorly understood, and may involve a change of the catalytic properties of the modified electrified interface apart from complex intermediate stabilisation. [148] Double layer effects and restructuration could also influence the CO 2 RR.…”

Efficient Electrocatalytic CO2Reduction Driven by Ionic Liquid Buffer‐Like Solutions

“…In 2011, it was shown that the CO 2 ‐reduction overpotential in aqueous electrolytes could be lowered drastically by adding the IL [EMIM][BF 4 ] (1‐ethyl‐3‐methylimidazolium tetrafluoroborate) to the electrolyte, a phenomenon that was attributed to complexation of the reduced “CO 2 .− ” by the IL . Since that initial report, a number of authors have demonstrated that ILs can promote CO 2 electroreduction at low overpotentials and at different electrode materials . However, the mechanism by which ILs lower reduction overpotentials has not yet been fully elucidated.…”

“…[13] Since that initial report, an umber of authors have demonstrated that ILs can promote CO 2 electroreduction at low overpotentials and at different electrode materials. [13][14][15][16][17][18][19][20][21] However,t he mechanism by which ILs lower reduction overpotentials has not yet been fully elucidated. It was proposed that lowering of the pH upon hydrolysis of [BF 4 ] À increases the conversion of CO 2 to CO, whereas adsorptiono f[ EMIM] + cations onto the electrode hinders protona dsorption and competitive H 2 evolution.…”