Electrochemical Reduction of Carbon Dioxide to Formic Acid in Ionic Liquid [Emim][N(CN)2]/Water System

The electrochemical reduction of CO₂ to formic acid or formate is a promising technology for addressing transfer and storage issues of current intermittent renewable energy resources. One of its main challenges is that the faradaic efficiency is low in the inorganic salt aqueous system because of the hydrogen evolution reaction is much easier than CO₂ electroreduction on most metal electrodes. Previous investigations have revealed that an ionic liquid system can provide desired products with the high faradaic efficiency and eliminate the hydrogen evolution reaction. However, this previously used ionic liquid system has a major pitfall because there is a net consumption of the ionic liquid in its reaction mechanism. In this manuscript, we present an alternate route, where 1-ethyl-3-methylimidazolium dicyanamide ([Emim][N(CN)₂]) aqueous solution is used to increase the solubility of CO₂ and suppress the water electrolysis without being consumed in the reaction. Cyclic voltammetry is performed in [Emim][N(CN)₂] aqueous solution on the Sn power electrode to determine the on-set potential of CO₂ electrolysis and its electrochemical stability. In addition, CO₂ electrolysis is carried out at various fixed potentials and concentrations of electrolyte to understand their effects on the faradaic efficiency. The maximum faradaic efficiency obtained during electrolysis is 81.9% towards the formation of formate at 1.8 V vs. Ag/AgCl and 0.5 mol L^-1 of ([Emim][N(CN)₂].