Quinone Reduction in Ionic Liquids for Electrochemical CO2 Separation

• Published in: ACS sustainable chemistry & engineering
• Main Authors: Gurkan, Burcu, Simeon, Fritz, Hatton, T. Alan
• Format: Journal Article
• Language: English
• Published: American Chemical Society 06.07.2015
• Subjects: Electrochemical separation; Quinone; Electrochemistry; Solvachromatism; Polarity; CO2 capture; Ionic liquid; Tricyanomethanide
• ISSN: 2168-0485; 2168-0485
• DOI: 10.1021/acssuschemeng.5b00116

We report the redox activity of quinone materials, in the presence of ionic liquids, with the ability to bind reversibly to CO2. The reduction potential at which 1,4-naphthoquinone transforms to the quinone dianion depends on the strength of the hydrogen-bonding characteristics of the ionic liquid solvent; under CO2, this transformation occurs at much lower potentials than in a CO2-inert environment. In the absence of CO2, two consecutive reduction steps are required to form first the radical anion and then the dianion, but with the quinones considered here, a single two-electron wave reduction with simultaneous binding of CO2 occurs. In particular, the 1,4-napthoquinone and 1-ethyl-3-methylimidazolium tricyanomethanide, [emim]­[tcm], system reported here shows a higher quinone solubility (0.6 and 1.9 mol·L–1 at 22 and 60 °C, respectively) compared to other ionic liquids and most common solvents. The high polarity determined through the Kamlet–Taft parameters for [emim]­[tcm] explains the measured solubility of quinone. The achieved high quinone solubility enables effective CO2 separation from the dilute gas mixture that is contact with the cathode by overcoming back-diffusive transport of CO2 from the anodic side.