Theoretical insights on the hydration of quinones as catholytes in aqueous redox flow batteries

Abstract

Abstract Quinones have been widely studied as a potential catholyte in water-based redox flow batteries (RFBs) due to their ability to carry both electrons and protons in aqueous solutions. The wide variety of quinones and derivatives offers exciting opportunities to optimize the device performance while poses theoretical challenges to quantify their electrochemical behavior as required for molecular design. Computational screening of target quinones with high performance is far from satisfactory. While solvation of quinones affects their potential application in RFBs in terms of both electrochemical windows, stability, and charge transport, experimental data for the solvation structure and solvation free energies are rarely available if not incomplete. Besides, conventional thermodynamic models are mostly unreliable to estimate the properties of direct interest for electrochemical applications. Here, we analyze the hydration free energies of more than 1,400 quinones by combining the first-principles calculations and the classical density functional theory. In order to attain chemical insights and possible trends, special attention is placed on the effects of “backbones” and functional groups on the solvation behavior. The theoretical results provide a thermodynamic basis for the design, synthesis, and screening of high-performance catholytes for electrical energy storage.