Selection of Low-Cost Ionic Liquid Electrocatalyst for CO2 Reduction in Propylene Carbonate/Tetrabutylammonium Perchlorate

Electrochemical reduction of carbon dioxide (CO2) to carbon monoxide (CO) has attracted increasing attention, because this method provides a new route for CO2 recycling utilization. As CO2 is chemically inert, this reaction requires a high over-potential. Therefore, it is highly desirable to develop an electrocatalyst to accelerate this reaction. In the present work, we have investigated numerous imidazolium ionic liquids (ILs) with the aim of looking for a low-cost homogeneous catalyst with high efficiency. By comparison, 1-butyl-3-methylimidazolium chloride ([Bmim][Cl]) has been selected as the most cost-effective. To further reduce the cost of [Bmim][Cl], we added [Bmim][Cl] into propylene carbonate(PC)/tetrabutylammonium perchlorate (Bu4NClO4), and used it as the electrocatalyst. Our experimental results show that [Bmim][Cl] has a high catalytic effect for CO2 reduction. The catalytic mechanism of [Bmim][Cl] has been discussed based on electrochemical impedance spectroscopy. It is explained as follows: CO2 was first reduced to the high-energy CO2 center dot(-) radical through a one-electron transfer. The generated CO2 center dot- radical further reacts with [Bmim](+), resulting in the formation of a complex [CO2-Bmim]. Thus, the activation energy of CO2 reduction has been reduced.