382601 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.