Issue 24, 2023

Nonionic oligo(ethylene glycol)-substituted viologen negolytes for aqueous organic redox flow batteries

Abstract

Viologen derivatives are attractive active materials for negolytes in aqueous organic redox flow batteries (AORFBs) owing to their fast kinetics and suitable reduction potentials. However, viologens with alkyl substitutions only (e.g., methyl viologen and ethyl viologen) suffer from poor stability and the insoluble nature of the second-electron product limits their energy density. A key to enabling durable and high-capacity viologen-based AORFBs lies in the molecular engineering of viologens. Here we demonstrated a series of oligo(ethylene glycol) (OEG) substituted viologens with improved cycling stability via the steric-hindrance effect and enhanced water solubility of the second-electron product. Electrochemical and symmetric cell investigations validated the high reversibility of tri(ethylene glycol) groups modified viologen (Vi-OEG3) and its improved solubility of the second-electron products in neutral aqueous solutions. When paired with a ferrocene-based posolyte, a full flow cell with Vi-OEG3 showed a much reduced capacity decay rate of 0.00253% per day or 0.000105% per cycle compared with ethyl viologen. This work expands the molecular design of viologens and shows an attractive viologen-based AORFB for low-cost and large-scale renewable energy storage systems.

Graphical abstract: Nonionic oligo(ethylene glycol)-substituted viologen negolytes for aqueous organic redox flow batteries

Supplementary files

Article information

Article type
Paper
Submitted
25 nov 2022
Accepted
28 mar 2023
First published
30 mar 2023

J. Mater. Chem. A, 2023,11, 12984-12991

Nonionic oligo(ethylene glycol)-substituted viologen negolytes for aqueous organic redox flow batteries

Y. Yao, W. Ma, J. Lei, Z. Wang, Y. Lu and L. Liu, J. Mater. Chem. A, 2023, 11, 12984 DOI: 10.1039/D2TA09177A

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