Five‐Membered‐Heterocycle Bridged Viologen with High Voltage and Superior Stability for Flow Battery

Abstract

Viologen and its derivatives have been widely investigated as the electroactive materials in aqueous flow batteries (AFBs). The high redox potential of viologen poses a challenge to the AFB's energy density when used as the negative electrolyte. A molecular engineering strategy is developed by inserting an electron‐rich π‐bridge unit (viz. thiophene, furan) between the two pyridiniums to lower the redox potential. The resultant 1,1′‐bis[3‐(trimethylamonium)propyl]‐4,4′‐(2,5‐thiophenediyl)bispyridinium tetrachloride ((ATBPy)Cl4) and 1,1′‐bis[3‐(trimethylamonium)propyl]‐4,4′‐(2,5‐furandiyl)bispyridinium tetrachloride ((AFBPy)Cl4) are investigated by a variety of physiochemical methods to track the structure of the molecule and its evolution during the electrochemical reaction. A flow battery is assembled to verify the applicability of (ATBPy)Cl4 with 1‐(1‐oxyl‐2,2,6,6‐tetramethylpiperidin‐4‐yl)‐1′‐(3‐(trimethylammonio)propyl)‐4,4′‐bipyridinium trichloride as the positive electrolyte. Run at the concentration of 1.0 m, the battery achieves a standard cell voltage of 1.51 V, capacity of 23.6 Ah L–1, energy efficiency of 85.7% at 60 mA cm–2, and a record peak power density of 302 mW cm–2, which outperform the reported viologen‐AFBs in literature. This work provides an effective strategy to develop electrochemically active compounds with tunable redox potential and superior chemical stability by molecule engineering.

Synthesis and Properties of Electron‐Deficient and Electron‐Rich Redox‐Active Ionic π‐Systems

“…Liang and his group used viologens such as V5 and V6 (Figure 2) as the negative electrolyte in aqueous organic flow batteries (AOFBs). [61] They have demonstrated the flow battery successfully by operating with a high concentration of 1.0 M. They have reported a battery of high capacity of 23.6 Ah L À 1 , the energy efficiency of 85.7 % at 60 mA cm À 2 with a standard cell voltage of 1.51 V. A peak power density of 302 mW cm À 2 and excellent cycling stability with a capacity decay rate of 0.008 % per cycle was achieved. Similarly, viologen V4 exhibits high cell voltage (1.57 V) and long cycling life (over 1000 cycles) in AOFBs.…”

“…synthesized 1,1‐bis[3‐(trimethylamonium)propyl]‐4,4‐(2,5‐furandiyl)bispyridinium tetrachloride V5 and 1,1′‐bis[3‐(trimethylammonium) propyl]‐4,4′‐(2,5‐thiophenediyl) bispyridinium tetrachloride V6 applying Suzuki coupling reactions (Scheme 2). [61] Thus, π‐bridging unit (viz. furan/thiophene) were inserted between the two pyridinium units.…”

“…Redox‐active heterocyclic compounds such as viologens are of particular interest due to their applications in redox‐flow batteries (RFBs). Liang and his group used viologens such as V5 and V6 (Figure 2) as the negative electrolyte in aqueous organic flow batteries (AOFBs) [61] . They have demonstrated the flow battery successfully by operating with a high concentration of 1.0 M. They have reported a battery of high capacity of 23.6 Ah L −1 , the energy efficiency of 85.7 % at 60 mA cm −2 with a standard cell voltage of 1.51 V. A peak power density of 302 mW cm −2 and excellent cycling stability with a capacity decay rate of 0.008 % per cycle was achieved.…”

Corannulene Extended Viologen-Based Ambipolar Polymers for Transparent-to-Color Electrochromic Supercapacitors

“…Viologens and extended viologens have been widely applied to redox-flow batteries and electrochromic devices as n-type materials because of their stable redox activity at negative potential. − The linear disubstituted viologens and extended viologens with high solubility in polar solvent were the most commonly used as redox-active additives in the electrolyte for supercapacitors and electrochromic smart windows. ,− However, the mixtures of viologens (or extended viologen) and electrolyte as bulk materials suffered from a slow electrochemical process due to the diffusion-controlled mechanism . The viologen substituted with a phosphonic acid end group absorbed on the surface of nanostructured anatase titanium dioxide displayed a short switching time of less than 5 s for an electrochromic device, solving the issue of achieving a high-efficiency device .…”

A high-capacity 1,2:3,4-dibenzophenazine anode integrated into carbon felt for an aqueous organic flow battery in alkaline media

“…At present, widely studied aqueous flow batteries (AFBs) utilize inorganic redox-active species, such as vanadium, 8 chromium 9 and bromine, 10 as well as organic ones ( e.g. , viologen, 11 phenazine, 12 anthraquinone, 13 nitroxyl radical 14 etc . ), to store electrical energy.…”