A Neutral‐pH Aqueous Redox Flow Battery Based on Sustainable Organic Electrolytes

Abstract

Aqueous organic redox flow batteries (AORFBs) have gained increasing attention for large-scale storage due to the advantages of decoupled energy and power, safe and sustainable chemistry, and tunability of the redox-active species. Here, we report the development of a neutral-pH AORFB assembled with a highly water-soluble ferrocene 1,1-disulfonic disodium salt (DSÀ Fc) and two viologen derivatives, 1,1'-bis(3-sulfonatopropyl)-viologen (BSPÀ Vi) and Bis(3-trimethylammonium)propyl viologen tetrachloride (BTMAPÀ Vi). Synthesized electrolytes showed excellent redox potential, good diffusion coefficient, and a good transfer rate constant. In particular, BSPÀ Vi has a more negative redox potential (-0.4 V) than BTMAPÀ Vi (À 0.3 V) and faster kinetics; therefore, it was selected to be assembled in an AORFB as anolyte, coupled with DSÀ Fc as catholyte.The resulting AORFB based on BTMAPÀ Vi/DSÀ Fc and BSPÀ Vi/DSÀ Fc redox couple had a high cell voltage (1.2 V and 1.3 V, respectively) and theoretical energy density (13 WhL À 1 and 14 WhL À 1 respectively) and was able to sustain 70 chargedischarge cycles with energy efficiency as high as 97 %.

Viologen-based aqueous organic redox flow batteries: materials synthesis, properties, and cell performance

“…BTMAP-Vi showed a permeability of 3.5 × 10 −6 cm 2 s −1 through a Nafion cation exchange membrane (CEM), much higher than that with an AEM. 65 Interestingly, negatively charged substituted viologens seem compatible with CEMs also as a result of charge repulsion. Sulfonate or phosphate based viologens exhibited low permeability across commercial CEMs ( e.g.…”

“…BTMAP-Vi showed a permeability of 3.5 × 10 −6 cm 2 s −1 through a Naon cation exchange membrane (CEM), much higher than that with an AEM. 65 Interestingly, negatively charged substituted viologens seem compatible with CEMs also as a result of charge repulsion. Sulfonate or phosphate based viologens exhibited low permeability across commercial CEMs (e.g., Naon, Fumasep E-620K), ranging from 2.20 × 10 −13 to 8.00 × 10 −9 cm 2 s −1 , and the E-620K membrane is more effective than the Naon membrane during the measurement of permeability of (SPr) 2 V. On the other hand, increasing the size of viologen molecules is also able to reduce the crossover through the membrane.…”

Development and Optimization of Air-Electrodes for Rechargeable Zn–Air Batteries

“…The dependence on fossil fuels for energy consumption should be minimized to limit further emissions of CO 2 in the atmosphere, and the fraction of electricity produced via renewables must be increased considerably [1,2], which today is limited by the absence of cheap battery technologies [3]. In this context, lithium-ion batteries are considered the most promising technology for energy storage applications and find widespread applicability in all portable electronics, electric and hybrid electric vehicles, and grid-scale energy storage systems [4,5]. Nevertheless, large-scale production of lithium-ion batteries for grid application needs to be improved for several reasons, including limited lithium availability, high cost, and poor safety [6][7][8].…”