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). However, a major issue in the use of quinones for ECCS is reactivity with O2 in the reduced state. Unfortunately, quinones are also known to suffer from a trade-off between their redox-potential and strength of binding to CO2, such that in general, quinones which do not react with O2 do not react strongly enough with CO2 to be of use. In this work, computational methods are used to explore how the carbonyl positioning, as well as the ring structure, of quinones affects the associated trade-offs. Using a model based on Hückel theory we show that the redox-potential of quinones strongly depends on the change in aromaticity upon reduction. It is then shown that by changing the quinone ring structure, it is possible to tune the redox potential by approximately 0.8 V. Finally, one new type of quinone, 2,3-naphthoquinone, is predicted to be a particularly promising candidate for ECCS, and NMR spectroscopy is utilised to demonstrate it capturing CO2 in the dianion state. Although 2,3-naphthoquinone lacks electrochemical reversibility, our study guides the design of redox-active molecules for future ECCS systems.