Efficient Electrochemical Reduction of CO2 to CO in Ionic Liquid/Propylene Carbonate Electrolyte on Ag Electrode

Fengyang Ju,Jinjin Zhang,Weiwei Lu

doi:10.3390/catal10101102

Abstract

The electrochemical reduction of CO2 is a promising way to recycle it to produce value-added chemicals and fuels. However, the requirement of high overpotential and the low solubility of CO2 in water severely limit their efficient conversion. To overcome these problems, in this work, a new type of electrolyte solution constituted by ionic liquids and propylene carbonate was used as the cathodic solution, to study the conversion of CO2 on an Ag electrode. The linear sweep voltammetry (LSV), Tafel characterization and electrochemical impedance spectroscopy (EIS) were used to study the catalytic effect and the mechanism of ionic liquids in electrochemical reduction of CO2. The LSV and Tafel characterization indicated that the chain length of 1-alkyl-3-methyl imidazolium cation had strong influences on the catalytic performance for CO2 conversion. The EIS analysis showed that the imidazolium cation that absorbed on the Ag electrode surface could stabilize the anion radical (CO2•−), leading to the enhanced efficiency of CO2 conversion. At last, the catalytic performance was also evaluated, and the results showed that Faradaic efficiency for CO as high as 98.5% and current density of 8.2 mA/cm2 could be achieved at −1.9 V (vs. Fc/Fc+).

Highlights

The unprecedented increase of CO2 concentration in the atmosphere has led to many concerns about global warming, and even predictable environmental disasters, which make us feel urged to limit the CO2 emission and effectively utilize them [1,2,3,4]
It has been reported that the main hurdle in CO2 electroreduction lay in the first-step one-electron reduction of CO2 to form an anion radical (CO2 − ), because this activation step requires a much high
The investigation on the alkyl length of imidazole-based ionic liquids (ILs) indicates that the IL of [Bmim]BF4 gives the lower onset potential and Tafel slope, as well as higher exchange current density, compared to other studied ILs and the traditional

Summary

Introduction

The unprecedented increase of CO2 concentration in the atmosphere has led to many concerns about global warming, and even predictable environmental disasters, which make us feel urged to limit the CO2 emission and effectively utilize them [1,2,3,4]. The electrochemical reduction of CO2 is regarded as the most prospective way, because it allows one to combine with carbon capture and storage technology, and to utilize renewable energy (such as solar energy and wind energy), as inputting energy and water as a reductant to reduce CO2 into various carbon-based fuels and chemicals (e.g., CO, HCOOH, CH4 , C2 H4, and CH3 OH) in a modular electrochemical reactor under ambient temperature and pressure [7,8,9,10,11]. The linear CO2 molecule is thermodynamically stable and kinetically inert to be reduced, due to its low electron affinity and large energy gap between its highest occupied molecular orbital (HOMO) and lowest unoccupied molecular orbital (LUMO) [23].

Methods

Results

Conclusion