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Abstract
Cost-effective anthraquinones, such as Alizarin, are promising for aqueous organic redox flow batteries (RFBs), but their low solubility limits the energy density of the electrolyte. Moreover, their degradation during cycling reduces battery lifespan. Here, we reveal molecular synergy
between Alizarin and its derivative, Alizarin Red S, which increases their combined solubility by 40%, from an expected 0.5 M (0.2 M Alizarin + 0.3 M Alizarin Red S, their practical individual solubility limits) to 0.7 M. Additionally, these interactions lead to a 40% reduction in capacity fade rate compared to a rule of mixtures prediction, demonstrating the stabilizing effects of molecular interactions in the binary electrolyte. Extending this approach to a ternary mixture with 2,6-DHAQ, we achieve a total concentration of 1 M, further demonstrating synergistic interactions. These findings highlight how mixtures of redox active molecules can unexpectedly enhance the stability and energy density of organic RFBs through molecular cooperativity.
Supplementary materials
Title
Supporting Information
Description
Experimental methods, Solubility measurement, CV comparison of Alizarin and Alizarin Red S, Binary and ternary negolyte – RFB cell performance measurements, Capacity fade rate versus concentration of Alizarin and Alizarin Red S, Electrochemical measurements and stability assessments of Alizarin Red S, Rule of Mixtures for capacity fade rate estimation, NMR analysis of binary negolyte capacity fade mechanism, Electrochemical regeneration strategy of ternary negolyte – RFB, CV measurements at oxidative potentials, COSY NMR spectroscopy, LC-MS analysis, NMR fitting equation, NMR studies of self-aggregation, Molecular interaction
investigation of ternary electrolyte.
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