Effect of additives in aqueous electrolytes on CO2 electroreduction

•Additives in aqueous electrolytes can enhance CO2 reduction activity and selectivity.•Additives can impact the interfacial properties such as local pH in CO2 reduction.•Selection of additives for CO2 electroreduction is complicated. Electrochemical reduction of CO2 (CO2ER) is a promising technology to mitigate the CO2 level in the atmosphere, as well as, to produce value-added chemicals and fuels. Aqueous solutions are regarded as the most common electrolytes for CO2ER. However, there are some challenges such as low CO2 solubility and the presence of parasitic hydrogen evolution reaction which cause CO2ER in aqueous electrolytes to be inefficient in terms of selectivity and activity. A number of strategies have been proposed to enhance the efficiency for CO2ER in aqueous electrolytes. Among them, introducing additives to the aqueous solutions has attracted considerable attention. Depending on the chemical and physical properties of the additives, they have been demonstrated to improve the selectivity and activity in CO2ER. Herein, we provide a review on classification, mechanism, challenges, and perspectives of the additives in the aqueous electrolytes for CO2ER.