Impacts of Quinone Structure on Trade-Offs Between Redox Potential and CO2 Binding Strength

Quinones are well-studied and promising candidates for redox-active sorbents in electrochemical CO2 capture and storage (ECCS). Unfortunately a persisting issue in this use of quinones is their dianions’ known reactivity with O2. While attempts have been made to tune the redox-potentials of quinones to avoid this, quinones which are more tolerant to the presence of O2, are also generally less reactive towards CO2, i.e. there is an inherent trade-off. Building off of prior work on anthraquinones and fluorinated benzoquinones [Bui et al., J.Phys.Chem.C., 126, 14163-14172, 2022], this study investigates how the trade-off varies for a wider range of quinone types. No single unifying trade-off is found; instead distinct quinone families follow distinct trade-offs. A Hückel model is utilised to demonstrate how the change in aromaticity upon two-electron reduction strongly influences the redox-potential, and that given the same change in aromaticity, ortho-quinones will possess a significantly more positive redox potential than non-ortho- quinones. By varying the carbonyl placement in otherwise unfunctionalised quinones, the redox-potential may be tuned by a range of up to 0.8 V. One previously uninvestigated quinone for ECCS, 2,3-naphthoquinone, is identified as particularly promising, and NMR spectroscopy shows its dianion capable of capturing CO2 but lacks electrochemical reversibility.