SSCU M. S. Thesis Colloquium
Name: Mr. Sandeep Kumar Sahoo
Research Supervisor: Prof. Satish Patil
Title: High-Voltage Organic Redox Electrolytes for Non-Aqueous Flow Batteries: Navigating Interdependent Performance Metrics
Date &Time: Monday, 30th March 2026 at 11:00 a.m.
Venue: ANZ Lecture Hall, Chemical Sciences Building
Abstract:
Non-aqueous organic redox flow batteries (NORFBs) represent a compelling architecture for large-scale renewable energy storage.1,2 However, the practical implementation of these systems is fundamentally constrained by a complex interplay of interdependent metrics: redox potential, chemical stability, reactivity of intermediates, and solubility.3 Generally, widening the electrochemical window accelerates molecular degradation, while structural modifications to enhance stability, such as extended π-conjugation, frequently compromise solubility.4 This work systematically addresses these challenges through two progressive molecular design strategies: rational design of asymmetric redox pairs and the development of amphoteric (bipolar) electrolytes.
Initially, we investigated an asymmetric redox pair consisting of acenaphthylene (Ac)-derived anolytes and cyano-functionalized dimethoxybenzene (DBBCN) catholytes. Electrochemical characterization reveals that this structural modification shifts the reduction potential 0.12 V more negative (–1.62 V vs. Ag+/Ag) while significantly enhancing durability. AcNI-TFSI retained 25.7% of its capacity after 50 cycles, nearly doubling the performance of its unprotected counterpart. Complementing this, the cyano-substitution of the dimethoxybenzene framework increased the oxidation potential by +0.20 V without sacrificing cycling stability. When integrated into an asymmetric flow cell, the AcNI-TFSI/DBBCN couple achieved Coulombic and energy efficiencies of 90% and 80%, respectively. While the cell remained susceptible to capacity fade from crossover and parasitic reactions, the results validate the efficacy of electronic tuning and steric protection in balancing voltage and stability.5
To further mitigate crossover-induced degradation, we explored the design of bipolar redox electrolytes capable of functioning as both anolyte and catholyte. We report the synthesis of 1,4-dihydropyrrolo[3,2-b]pyrrole (DHPP) derivatives, which demonstrate amphoteric characteristics and exceptional solubility (up to 1.0 M) in acetonitrile. Electrochemical studies confirmed that DHPP derivatives possess diffusion coefficients(4×10-5cm2s-1) and rate constants(1×10-2cm.s-1) well-suited for flow cell applications. Symmetric flow cells utilizing DHPP delivered a high open-circuit voltage of 2.54 V with excellent bipolar reversibility and moderate cycling stability. Overall, this work provides a rational framework for navigating the trade-offs in organic electrolyte design, offering a systematic path toward stable, high-voltage, and highly soluble NORFBs for grid-scale energy storage.
References:
(1) Alotto, P. et al. Renewable and Sustainable Energy Reviews 2014, 29, 325–335.
(2) Sánchez-Díez, E. et al. J. Power Sources 2021, 481, 228804.
(3) Luo, J. et al. ACS Energy Lett. 2019, 4 (9), 2220–2240.
(4) Ahn, S. et al. Chem. Soc. Rev. 2025, 54 (2), 742–789.
(5) Sandeep K.S., et al. Chem. Mat. 2026, Manuscript ID: cm-2025-02775u (Under Revision)
