High performance carbon dioxide electroreduction in ionic liquids with in situ shell-isolated nanoparticle-enhanced Raman spectroscopy

Electrochemical CO2 reduction (ECR) has received significant attention with the rising emphasis on renewable energy. However, high Faradaic efficiency (FE) and large current density are still the challenge for ECR. Selecting ionic liquids (ILs) as electrolytes for ECR has advantages of enhancing the FE and improving the current density. Herein, in situ shell-isolated nanoparticle-enhanced Raman spectroscopy (SHINERS) is employed to study the ECR process on nickel foam (NF) in imidazolium ILs. Results show that the IL 1-Butyl-3-methylimidazolium chloride (BmimCl) presents the best performance towards ECR. The FE of CO is as high as 94.6 %, with a considerable current density of 72 mA cm−2. Particularly, the FE of CO can keep around 82 % after 15 h continuous electrolysis, indicating the good stability. Structural details of the BmimCl-NF electrode interface are obtained by in situ SHINERS along with density functional theory (DFT) calculations, indicating that the adsorption configuration change of imidazolium cations of BmimCl on NF electrode is favorable for ECR. Moreover, the strong interaction between Cl anions of BmimCl and CO2 could bend and activate the CO2 molecules. The reaction intermediate CO32– confirmed by in situ SHINERS helps to determine the reaction pathway. Particularly, the DFT calculations show the priority of the ECR reaction on Ni surface for CO product. This work presents a promising method for in situ studies of the CO2 electroreduction mechanism in ionic liquids.