Investigation of Alkyl Amine Substituted Quinone Derivatives for the Redox Flow Battery Applications in Acidic Medium

Abstract

2,5-bis((dimethylamino)methyl)benzene-1,4-diol (H2QDMA), a redox-active molecule and its derivatives are synthesised by a one-step chemical method using Mannich reaction has been explored as catholyte with vanadium (V2+/V3+) anolyte for aqueous redox flow battery applications. The solubility of H2QDMA was ∼ 0.75 M in 3 M H2SO4. H2QDMA showed one sharp redox peak at the formal potential 0.6 V ± vs Ag/AgCl, and it was stable for 100 continuous CV cycles without any appreciable change in colour. The battery delivered a discharge capacity of ∼ 2 Ah L−1, which faded with cycles. We have carried out a post cycle analysis of catholyte and anolyte to understand the origin of the capacity fading. Towards this, the oxidized form of H2QDMA, i.e., QDMA, was synthesized. The stability of QDMA in acidic solution was low, and the colour of the solution changed to intense brown with time. The UV–Visible spectrum and CV curves of the QDMA reflects the same behaviour as observed with the catholyte solution obtained post galvanostatic charge-discharge analysis. This study concluded that the QDMA undergoes faster chemical transformation, presumably through the Michael addition reaction process, compared to its participation in the desired electrochemical process.