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

Abstract

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 C₁ products (i.e. CO and formate) to C₂₊ products (i.e. ethylene, ethanol, and oxalic acid). The product distribution, i.e. the ratio of C₁ 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.