Study On The Effect And Mechanism Of Electrolyte Compositions On The Electroreduction Of CO₂

In order to investigate the effect of solvent and supporting electrolyte on the electroreduction of CO2, cyclic voltammetry (CV) and constant potential electrolysis (CPE) experiments were conducted on Ag electrode in a three-electrodes electrolytic cell. The results show that the Faradic efficency of CO obtained in acetonitrile is highest compared to that in other two solvents investigated (methanol and DMF). Additionally, the overpotential of CO2 reduction decreases and the partial current density of CO increases when using the strong acid as the supporting electrolyte in the anolyte. And the overall efficency for CO2 reduction is further enhenced with the ionic liquid (IL) as the supporting electrolyte in the catholyte. Through the asjustment of the composition of IL to explore its catalytic mechanism, the results show that the cationic group of IL has an important effect on the value of CDco-Based on this observation, it can be confirmed that it is imidazole cation plays the main catalytic effect rather than the anion group. Effect of the alkyl chain length on the Nl-position in imidazolium cation (MIM+) on the electroreduction of CO2 was then investigated. The onset potential for CO2 reduction shifts to the increasingly negative potential with the increase of the size of the substitute attached to the N1-position of MIM+. Density functional theory (DFT) computations suggest the shift of onset potential of CO2 reduction is related to the association degree between MIM+and electrogenerated CO2-species. More importantly, preparative scale electrolysis indicates the selectivity and output rate for the aimed product CO are also significantly affected by MIM+.With the elongation of the alkyl group in MIM+from ethyl to octyl, the Faradaic efficiency for CO (FEco) first drastically increases from 87+4% to 97+2%, but then keeps almost unchanged at high levels. However, the curve of the current density (CD) with chain length shows a convex property. Keeping other experiment conditions unchanged, if depositing a layer of thin film of nanoparticle silver on the Ag plate cathode electrode, the current density increased obviously. Therefore, the nanoparticle silver is helpful to improve the efficiency of CO2 reduction.