A Quantitative Analysis of Electrochemical CO₂ Reduction on Copper in Organic Amide and Nitrile-Based Electrolytes

Aqueous electrolytes used in CO2 electroreductiontypicallyhave a CO2 solubility of around 34 mM under ambient conditions,contributing to mass transfer limitations in the system. Non-aqueouselectrolytes exhibit higher CO2 solubility (by 5-8-fold)and also provide possibilities to suppress the undesired hydrogenevolution reaction (HER). On the other hand, a proton donor is neededto produce many of the products commonly obtained with aqueous electrolytes.This work investigates the electrochemical CO2 reductionperformance of copper in non-aqueous electrolytes based on dimethylformamide(DMF), n-methyl-2-pyrrolidone (NMP), and acetonitrile(ACN). The main objective is to analyze whether non-aqueous electrolytesare a viable alternative to aqueous electrolytes for hydrocarbon production.Additionally, the effects of aqueous/non-aqueous anolytes, membrane,and the selection of a potential window on the electrochemical CO2 reduction performance are addressed in this study. Experimentswith pure DMF and NMP mainly produced oxalate with a faradaic efficiency(FE) reaching >80%; however, pure ACN mainly produced hydrogenandformate due to the presence of more residual water in the system.Addition of 5% (v/v) water to the non-aqueous electrolytes resultedin increased HER and formate production with negligible hydrocarbonproduction. Hence, we conclude that aqueous electrolytes remain abetter choice for the production of hydrocarbons and alcohols on acopper electrode, while organic electrolytes based on DMF and NMPcan be used to obtain a high selectivity toward oxalate and formate.