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Electro-reduction of carbon dioxide (CO2) to carbon monoxide (CO) has been extensively studied on metal and alloy electrodes for many decades. However, owing to their disadvantages of low current density and high over-potential, the practical application of these electrodes has been limited. Hence, it is highly desirable to explore new and high efficient electrode for CO2 reduction to CO. Ag2S has been widely studied as electrode material in electrochemistry due to its unique properties, such as high conductivity, chemical stability, and easy to be prepared. In this work, we have fabricated an Ag2S electrode via electro-oxidation of Ag in aqueous solution. X-ray diffraction (XRD) and scanning electron microscope (SEM) confirm that Ag2S has been modified on Ag foil, which made the electrode surface roughness. And then, we have evaluated the performance of Ag2S electrode as the cathode for CO2 reduction in propylene carbonate/tetrabutylammonium perchlorate. The cathodic current density reaches to 9.85 mA/cm2, with the faradic efficiency for CO formation remaining stable at 92% during 4 h long-term electrolysis. [ABSTRACT FROM AUTHOR]

Abstract: 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.− radical through a one‐electron transfer. The generated CO2.− radical further reacts with [Bmim]+, resulting in the formation of a complex [CO2−Bmim]. Thus, the activation energy of CO2 reduction has been reduced. [ABSTRACT FROM AUTHOR]