Abstract
Redox-flow batteries (RFBs) can store large amounts of electrical energy from variable sources, such as solar and wind. Recently, redox-active organic molecules in aqueous RFBs have drawn substantial attention due to their rapid kinetics and low membrane crossover rates. Drawing inspiration from nature, here we report a high-performance aqueous RFB utilizing an organic redox compound, alloxazine, which is a tautomer of the isoalloxazine backbone of vitamin B2. It can be synthesized in high yield at room temperature by single-step coupling of inexpensive o-phenylenediamine derivatives and alloxan. The highly alkaline-soluble alloxazine 7/8-carboxylic acid produces a RFB exhibiting open-circuit voltage approaching 1.2 V and current efficiency and capacity retention exceeding 99.7% and 99.98% per cycle, respectively. Theoretical studies indicate that structural modification of alloxazine with electron-donating groups should allow further increases in battery voltage. As an aza-aromatic molecule that undergoes reversible redox cycling in aqueous electrolyte, alloxazine represents a class of radical-free redox-active organics for use in large-scale energy storage. Redox-flow batteries with organic-based electrolytes hold many advantages over conventional-flow batteries. Here the authors report a high-performance flow battery based on alloxazine, an aqueous-stable and soluble redox-active organic molecule resembling the backbone structure of vitamin B2.
Highlights
IntroductionDrawing inspiration from nature, here we report a high-performance aqueous Redox flow batteries (RFBs) utilizing an organic redox compound, alloxazine, which is a tautomer of vitamin B2’s isoalloxazine backbone
Since the invention of Redox flow batteries (RFBs) in the 1970s, the development efforts for its electrolyte materials – the core component of RFBs – have concentrated on single metal ions such as vanadium, iron and chromium, where the battery voltages are fixed by the reduction potentials of these ions, and their solubilities and stabilities are governed by the pH and composition of the supporting electrolyte.[6,7]
Besides the large shift in reduction potential moving from isoalloxazine to alloxazine, we observed a significant increase in chemical stability in alkaline conditions
Summary
Drawing inspiration from nature, here we report a high-performance aqueous RFB utilizing an organic redox compound, alloxazine, which is a tautomer of vitamin B2’s isoalloxazine backbone. Improved methods for storing electrical energy from intermittent renewable sources are needed to support the rapid deployment of photovoltaic (PV) and wind power.[1,2,3] A promising approach for safe and cost-effective stationary energy storage uses redox flow batteries (RFBs), in which the energy is stored in fluids held outside the power conversion electrochemical cell.[4,5] This permits the independent engineering of energy (electrolyte volume and/or concentration) and power (cell area) capacities and enables the attainment of the high energy-to-power ratios (i.e. long discharge durations at rated power) necessary to deliver energy from PV and wind when it is needed. Since the invention of RFBs in the 1970s, the development efforts for its electrolyte materials – the core component of RFBs – have concentrated on single metal ions such as vanadium, iron and chromium, where the battery voltages are fixed by the reduction potentials of these ions, and their solubilities and stabilities are governed by the pH and composition of the supporting electrolyte.[6,7] their development has been impeded by one or more shortcomings such as high electrolyte corrosivity, toxicity, cost, membrane crossover rate, or sluggish reaction kinetics
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