Effects of electrolytes on the electrochemical reduction of CO to CH: a mechanistic point of view

The most attractive strategy to mitigate energy shortages and environmental pollution caused by fossil fuel consumption and CO 2 emissions is to utilize renewable clean energy and convert CO 2 into high value-added chemical products. However, it has been proven that activation and reduction of CO 2 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 CO 2 into chemicals, ranging from common C 1 products ( i.e. CO and formate) to C 2+ products ( i.e. ethylene, ethanol, and oxalic acid). The product distribution, i.e. the ratio of C 1 to C 2+ , 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 C 2+ products (especially ethylene) in the electroreduction of CO 2 and propose the mechanism of C-C coupling and possible reaction pathways, aiming to better understand the role of electrolytes in the electroreduction of CO 2 to C 2+ products and to provide insights into the field of process optimization for the electrochemical conversion of CO 2 to high value-added chemicals and fuels. In recent years, ionic liquids have received widespread attention due to their high solubility for CO 2 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 CO 2 . Electrolyte plays an important role in the electroreduction of CO 2 . This review summarizes the mechanism of C 2 H 4 formation and the effect of pH, cations and anions of traditional electrolytes as well as ionic liquids.