In Situ Investigations of Bromine‐Storing Complex Formation in a Zinc‐Flow Battery at Gold Electrodes

Abstract

One of the most promising candidates for affordable energy storage systems for electric vehicles is the zinc/bromine battery. The reversible cell voltage of 1.82 V, a theoretical specific energy of 430 Wh kg Ϫ1 , robustness, high cycle life, unlimited standby periods in the charged or discharged state, low self-discharge rates, and operation at ambient temperature explain the scientific and industrial interest in this system. [1][2][3][4] Zinc is deposited at the negative electrode and elemental bromine is formed at the positive electrode during charging of the zinc/ bromine battery Zn 2ϩ ϩ 2e Ϫ r Zn [1] 2Br Ϫ r Br 2 ϩ 2e Ϫ [2]

Battery Technologies for Large-Scale Stationary Energy Storage

“…An aqueous solution of zinc bromide, which is the battery discharge product, is circulated through the two compartments of the cell from two separate tanks. Bromine is stored adsorbed on porous media or in the form of a complex with quaternary ammonium cations that is in equilibrium with an aqueous bromine-containing phase (97). The reaction chemistry is:…”

Systematic Study of Quaternary Ammonium Cations for Bromine Sequestering Application in High Energy Density Electrolytes for Hydrogen Bromine Redox Flow Batteries

“…Stabilization of polybromides by conversion into a less volatile form would reduce the bromine vapor pressure, thus leading to a safer battery electrolyte [ 7 ]. Additives used to lower bromine’s volatility have been applied in zinc bromine RFB (Zn/Br 2 -RFB) [ 8 , 27 , 28 , 29 , 30 , 31 , 32 , 33 , 34 , 35 , 36 , 37 , 38 , 39 ] and vanadium bromine RFB (V/Br 2 -RFB) [ 40 , 41 ] electrolytes for a long time. These additives are mostly based on organic quaternary ammonium cation compounds and are called bromine complexing agents (BCA).…”

“…This heavy phase is often referred as the fused salt phase (fs), which sometimes tends to crystallize [ 31 , 42 ]. In the past, many BCAs have been evaluated for their application on zinc bromine batteries, out of which BCAs such as 1-ethyl-1-methylpyrrolidin-1-ium bromide [MEP]Br and 1-ethyl-1-methylmorpholin-1-ium bromide [MEM]Br [ 8 , 27 , 28 , 29 , 30 , 31 , 32 , 33 , 34 , 38 , 39 , 42 , 43 ] have received a lot of attention and have been investigated thoroughly. Other BCA structures such as heteroaromatic BCAs based on alkylated pyridine, picolines or imidazole [ 27 , 29 , 30 , 34 , 44 ], symmetrical and unsymmetrical alkylated aliphatic BCAs [ 33 , 40 , 42 ] and alkylated cyclic cations [ 27 , 29 , 36 , 42 ] have also been reported in the literature.…”

“…Polar side chain groups of BCAs have been found to also increase the solubility of the BCA in aqueous solutions. Mixtures of BCAs have been chosen to overlap the positive properties of different BCAs and overcome the drawbacks of single BCA properties [ 34 , 38 , 40 , 41 , 42 , 43 ].…”

Visible‐Light‐Mediated Addition of α‐Aminoalkyl Radicals to [60]Fullerene by Using Photoredox Catalysts

“…Polyhalide‐based ILs have been used as reagents or reagent/media in halogenation reactions64 and as electrolytes in redox systems (I – /[I 3 ] – ) 65. Moreover, they play an essential role in dye‐sensitized thin‐film solar cells,66 high‐power67 and zinc‐bromine batteries,68 or as antimicrobial filters and textiles 69…”