(368b) Electrocatalysts for CO2 Electroreduction in Ionic Liquids

Carbon dioxide utilization through electroreduction to CO and/or other chemicals offers opportunities for re-harnessing some of the carbon released through combustion when paired with a carbon-neutral electricity source.  CO₂ electroreduction can lead to a wide variety of products ranging from CO to C₂ and C₃ hydrocarbons, alcohols and beyond.  Significant strides are still needed before commercialization of CO₂ electroreduction can be realized.  Aqueous-based CO₂ electroreduction suffers from parasitic H₂ production where the reduction of water is favored over that of CO₂ at the potentials required for CO₂ activity.  The non-H₂ product distribution is commonly broad making selectivity a challenge as well.

                The challenges of product distribution and H₂ generation could be addressed by replacing the aqueous system with an ionic liquid (IL) system.  ILs, ionic salts with melting points below 100°C, generally have minimal vapor pressures, are conductive, and have moderate-to-high viscosities.  Many ILs have electrochemical potential windows substantially wider than water.  This allows for CO₂ electroreduction potentials to be reached without the degradation of the solvent like what occurs in water.  The IL anion and cation can be tuned to have enhanced CO₂ solubility which increases reactant availability at the electrode surface.  Additionally, the lack of available protons in IL systems limits the products to primarily CO and oxalate, making selectivity much more controllable.

While the benefits of using ILs for CO₂ electroreduction are promising, they are not drop-in replacement solvents/electrolytes.  The ILs can be passivating towards metals, ligating effects of the ILs can block active sites and the extended double layers can inhibit mass transfer.  Electrocatalytic systems have to be designed for IL use to be successful.

                We have investigated copper catalysts for CO₂ electroreduction in ILs with high CO₂ solubilities such as 1-butyl, 3-methylimidazolium bis(trifluoromethylsulfonyl)imide ([Bmim][NTf₂]).  The impact of electrochemical conditions and morphology of the catalyst on activity, faradaic efficiency and product distribution will be reported.