Effects of electrolytes on the electrochemical reduction of CO2 to C2H4: a mechanistic point of view

The most attractive strategy to mitigate energy shortages and environmental pollution caused by fossil fuel consumption and CO2 emissions is to utilize renewable clean energy and convert CO2 into high value-added chemical products. However, it has been proven that activation and reduction of CO2 is a great challenge because of their thermodynamic stability and kinetic inertness. Recently, electrochemical conversion has emerged as one of the most flourishing means of converting CO2 into chemicals, ranging from common C-1 products (i.e. CO and formate) to C2+ products (i.e. ethylene, ethanol, and oxalic acid). The product distribution, i.e. the ratio of C-1 to C2+, is primarily determined by the electrode potential, cathode catalyst and electrolyte. Among them, the electrolyte plays a significant role in the total reaction efficiency and product selectivity. Here, we give a mini-review of the recently reported effects of various electrolytes on the selectivity to C2+ products (especially ethylene) in the electroreduction of CO2 and propose the mechanism of C-C coupling and possible reaction pathways, aiming to better understand the role of electrolytes in the electroreduction of CO2 to C2+ products and to provide insights into the field of process optimization for the electrochemical conversion of CO2 to high value-added chemicals and fuels. In recent years, ionic liquids have received widespread attention due to their high solubility for CO2 and the designability of their structures. They are generally considered as a green and efficient medium for homogeneous and heterogeneous catalytic reactions under ambient conditions. Here, we also briefly introduce some studies on ionic liquids used in the electrochemical reduction of CO2.