Uncovering benzoquinone derivatives for redox flow batteries: DFT insights on reduction potentials and solvent effects

Quinones possess high redox potential, making them suitable for organic redox-flow batteries. Their oxidation and discharge during charging involve two reversible electron transfer reactions. This study utilized density functional theory (DFT) with the B3LYP functional and 6-31G(d) basis set to calculate the first and second reduction potentials of benzoquinones (BQ). Various BQ derivatives were created by adding electron-donating substituents (-NHCH3, -NH2, -OCH3, -NHCOCH3, -OCOCH3). The universal solvation model (SMD) assessed solvent effects, while lithium salts, solvation-free energy, and HOMO-LUMO energies influenced reduction potentials. The -OCOCH₃-substituted BQ showed the highest first and second redox potentials at 2.81 V and 2.27 V, respectively. Adding boron trifluoride (BF3) salt increased these potentials to 3.99 V and 3.84 V. The electrochemical behavior of BQ and its derivatives was examined in three solvents: carbon tetrachloride (CCl₄), acetonitrile (ACN), and water (H₂O). The average reduction potentials in these solvents followed the trend CCl₄ < ACN < H₂O, with water being the most effective due to its hydrogen bonding and polarity. These findings highlight the significant impact of solvent characteristics on electrochemical processes. KEYWORDs: Benzoquinone derivatives, DFT, Electron affinity, Reduction potential, Redox flow battery, Solvation-free energy, SMD solvation model Bull. Chem. Soc. Ethiop. 2025, 39(2), 381-396.                                                                 DOI: https://dx.doi.org/10.4314/bcse.v39i2.15