Synthesis and Characterisation of Novel Additives for Use in the Hybrid ZnBr ₂ Flow Battery

Abstract

Zinc-bromine redox flow batteries (RFB) are energy storage devices capable of integrating with renewable generators and so improve energy management from these intermittent sources. However, this system is susceptible to self-discharge via the electrogenerated bromine transferring through the separator and reacting with the plated zinc. Here we examine the use of novel quaternary ammonium complexes to capture the electrogenerated bromine but keep it in the aqueous phase (as opposed to the immiscible phase formed with N-methyl-N-ethylpyrrolidinium, MEP). Electrochemical analysis indicates that these complexes do not impact on the electrode kinetics and exhibit similar physical properties as to the MEP. However, the latter still shows an enhanced ability to complex the bromine to higher polybromide states (i.e. Br 5 −).

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

“…In previous studies, [C2MM]Br and [C2MP]Br have been applied in electrolytes for Zn/Br 2 -RFB individually or in mixtures [ 8 , 28 , 30 , 33 , 38 , 41 , 42 , 43 ]. While the liquid fused salts of the Zn/Br 2 electrolytes are stable at room temperature, these BCA form crystals for the selected acidic concentration at different SoC of a H 2 /Br 2 -RFB electrolyte.…”

“…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.…”

The characteristics and performance of hybrid redox flow batteries with zinc negative electrodes for energy storage

“…Research continues on the development of more stable quaternary ammonium salts as complexing agents, as in the work by Bryans et al [72]. In addition to potential measurements, the SOC can be monitored by determining the concentration of ZnBr2 in the negative electrolyte via Raman spectroscopy [73].…”

Higher Voltage Redox Flow Batteries with Hybrid Acid and Base Electrolytes

“…The energy capacity of a flow battery will increase by enlarging the size of the storage tanks and the output power can be manipulated via modification of the battery cell. [14] Metal ion-based flow batteries, such as all-vanadium, iron-chromium and zinc-bromine flow batteries are commercially available, however, they face great challenges such as high material cost, [15] slow kinetics, [16][17][18] precipitation [19] and corrosion [20,21] (for all-vanadium flow batteries), side reactions, [17] efficiency [17] and corrosion (for iron-chromium flow batteries), dendrite formation, [22] environmental hazards related to maintaining all components in solution phase [23] and requirements for cooling [24] (for zincbromine flow batteries). In comparison, organic flow batteries can serve as a reliable alternative for lowering material costs and improving kinetics.…”