(Invited) Using Ionic Liquid and Organic Salt Additives to Modify CO2 Electroreduction Selectivity on Copper

Abstract

Copper is the only metal that can be used as an electrocatalyst to produce hydrocarbons and alcohols in CO2 electroreduction. Controlling selectivity to specific products is very challenging, limiting the viability of CO2 electroreduction on copper to synthesize fuels or chemicals. To obtain products that contain hydrogen, aqueous electrolytes are generally necessary, which also leads to competition with hydrogen evolution reaction (HER). By using ionic additives such as organic salts and ionic liquids, the water and CO2 concentrations at the interface during CO2 electroreduction can be modified. By changing the species at the electrode interface, the product selectivity can be modified. We have found when using dilute concentrations of additives that the anion has more influence on product selectivity. For example, when 10 mM of 1-butyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide [BMIM][NTF2] or 10 mM of Na[NTf2] is used in 0.1M KHO3, the product selectivities are very similar, promoting formate formation. When 1-butyl-3-methylimidazolium dicyanamide [BMIM][DCA] or 10 mM of Na[DCA] is used in 0.1M KHO3, CO2 electroreduction is substantially suppressed and HER is promoted. The hydrophobic and CO2-phillic [NTf2] likely limits the water available at the surface while increasing the concentration of CO2. The hydrophilic and CO2-phobic [DCA] likely increases the water available at the surface and diminishes the concentration of CO2 available for reaction.