Biomimetic Naphthoquinone Zwitterion Derivative with Water-Solubilizing Amino Acid Side Chain for High-Stability Aqueous Redox Flow Batteries
Yuzhu Liu, Pengbo Zhang, Zuoao Wu, Guochun Ding, Xinmei Song, Jing Ma, Wei Wang, Xizhang Wang, Zhong Jin
Abstract
Aqueous organic redox flow batteries (AORFBs) have gained attention as an alternative to transition metal ion-based flow batteries. Upgrading the functional groups and modification positions is crucial to regulating the redox potential, solubility, and stability of organic species. Herein, we introduce high-performance alkaline AORFBs using 3-(2-chloro-1,4-naphthoquinon-3-ylamino)propanoic acid (3-AFNQ), a biomimetic naphthoquinone zwitterion with a water-solubilizing amino acid group at the 3-position. Similar to natural amino acids, 3-AFNQ is a zwitterion with an asymmetric charge distribution. The hydrogen bonds between the amino acid group and water molecules enhance the aqueous solubility. The rational molecular design of 3-AFNQ prevents enol–ketone tautomerization, ensuring high reversibility, good redox kinetics, and stability when it is used as a negolyte. The AORFBs based on 3-AFNQ negolyte exhibit a 0.39% capacity fade rate per day at high concentration. These results underscore the significance of rational molecular design in avoiding molecular degradation and expanding naphthoquinone derivatives’ potential applications in AORFBs.