Trade-off between redox potential and strength of electrochemical CO2 capture in quinones

Abstract

Electrochemical carbon dioxide capture has recently emerged as a promising alternative approach to conven- tional energy-intensive carbon capture methods. The most common electrochemical capture approach is to employ redox-active molecules such as quinones. Upon electrochemical reduction, quinones become activated for the chemical capture of CO2. The main disadvantage of this method is the possibility of side-reactions with oxygen, which is present in almost all gas mixtures of interest for carbon capture. This issue can potentially be mitigated by fine-tuning redox potentials through the introduction of electron-withdrawing groups on the quinone ring. In this article, we investigate the thermodynamics of the electron transfer and chemical steps of CO2 capture in different anthraquinone derivatives with a range of substituents. By combining density functional theory calculations and cyclic voltammetry experiments, we discover a trade-off between redox potentials and the strength of CO2 capture. We show that redox potentials can readily be tuned to more positive values to impart stability to oxygen, but as a consequence, significant decreases in CO2 binding free energies are observed. This trade-off must be taken into consideration for the design of improved redox active molecules for electrochemical CO2 capture.