Viologen/Bromide Dual-Redox Electrochemical Capacitor with Two-Electron Reduction of Viologen

Abstract

In this work, we report a novel dual-redox electrochemical capacitor (EC) using a modified viologen (V) as anolyte and bromide (Br) as catholyte. In general, modified viologens are dications. When they are used as anolyte in aqueous dual-redox ECs, only one-electron reduction reaction can occur, because most divalent and monovalent viologens are soluble but zerovalent viologens are insoluble. The insoluble and nonconductive zerovalent viologens will block the surface of the activated carbon electrode from subsequent reactions. The energy densities of the dual-redox ECs using viologens are expected to be greatly improved if those viologens can carry out multiple electron reduction reactions. In this work, 1,1′-bis[3-(trimethylammonio)propyl]-4,4′bipyridinium (NV 4+ ), a tetra-cationic viologen, has been used as anolyte for dual-redox EC. NV 2+ produced by two-electron reduction of NV 4+ is highly soluble in aqueous solution, so that two consecutive one-electron reductions of viologen can be utilized in dual-redox ECs. To further solve the cross-diffusion issue of the charging products, Br 3 − and NV cations, of the positive and the negative electrodes, we have used tetrapropyl ammonium cation (TPA + ) to complex Br 3 − , and quaternized styrene ethylene butylene styrene (SEBS-QA) anion exchange membrane (M) to block the cross-diffusion of NV cation. The obtained NV/TPA/Br-M (NV 4+ /TPA + /Br − electrolyte with SEBS-QA membrane) dual-redox EC exhibits an average Coulombic efficiency over 99%. It also provides a high specific energy of 87 Wh/kg dry at 1 A/g dry and a peak power density of 4.8 kW/kg dry at 5 A/g dry . The functions of TPA + and SEBS-QA membrane were characterized and are discussed in detail.

Polymeric Ion Conductors Based on Sono‐Polymerized Zwitterionic Polymers for Electrochromic Supercapacitors with Improved Shelf‐Life Stability

“…As a result, DHV +• and dmFc + return to original DHV 2+ and dmFc, by which the device is bleached and discharged. [46,48] The presence of ZI moieties in the gel delayed this self-discharging process. For example, it took ≈9000 s for the ZI gel-based ECS to be fully self-discharged, whereas the PS-r-PMMA gel-based ECS reached 0.0 V within ≈3700 s (Figure 5b).…”

Electrochemical Capacitors with Confined Redox Electrolytes and Porous Electrodes

“…Similar as those conducted for inorganic redox electrolytes, multiple organic redox additives (e.g., HQ + PPD [ 37a ] ) and organic species with multiple redox centers have been added in aqueous solutions for the R‐EC construction. The latter redox species include 1,1′‐bis[3‐(trimethylammonio)‐propyl]‐4,4′‐bipyridinium tetrabromide (NVBr 4 ), [ 56 ] ethyl viologen dibromide (EVBr 2 ), [ 43v ] methyl viologen dibromide (MVBr 2 ), [ 31 ] heptyl viologen dibromide (HVBr 2 ), [ 31 ] pentyl viologen dibromide, [ 43y ] etc. For instance, EVBr 2 possesses redox‐active bipyridinium cation and bromide anion, its redox reactions can thus occur at the negative and positive electrodes, respectively.…”

Recent progress in electrochromic energy storage materials and devices: a minireview

“…To resolve this issue, the 1,1 0 -bis [3-(trimethylammonio)propyl]-4,4 0 -bipyridinium (NV 4+ ) molecule, which transforms into an NV 2+ redox state by accepting two electrons and shows high solubility in an aqueous solution, is used. 97 The redox property is due to the presence of electrolyte viologen (NV 4+ /NV 2+ ; act as an anolyte) and bromide (Br; act as a catholyte) ions. To solve the cross-diffusion issues of these species, the tetrapropyl ammonium cation (TPA + ) and the quaternized styrene ethylene butylene styrene membrane (SEBS-QA) are used to make a complex with the Br 3À anion and the NV cation, respectively.…”