Hydrogen‐Bromine Redox‐Flow Battery Cycling with Bromine Complexing Agent: on the Benefits of Nanoporous Separator Versus Proton Exchange Membrane

Abstract

The reversible and fast redox kinetics of bromine/bromide makes it a desirable couple as a catholyte in redox‐flow batteries (RFBs). In principle, the highest possible energy density is obtained with hydrogen‐bromine RFBs. Bromine sequestration agents, also called bromine complexing agents (BCAs), bind bromine in a non‐miscible phase and can, therefore, reduce the vapor pressure of bromine, mitigate its crossover, and result in higher practical range of electrolyte concentration. Therefore, BCAs can enhance the battery's safety and competitivity by significantly decreasing the cost of components. To date, BCAs are commonly used in membrane‐free bromine systems, which cannot provide the high current density demonstrated in hydrogen‐bromine RFBs. Herein, the drastic limitations encountered are shown while operating a hydrogen‐bromine RFB with a standard perfluorinated sulfonic acid membrane due to the strong BCA–perfluorinated sulfonic acid interaction. On the other hand, the benefits of using a polyvinylidene difluoride‐silica (PVDF–SiO2) nanoporous separator are demonstrated, which does not interact with the BCA. In this approach, the hydrogen‐bromine RFB can sustain cycling, albeit at a more moderate current than a BCA‐free battery.

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

“…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. Different side chains in N-position such as n -alkyl [ 27 , 29 , 31 , 33 , 34 , 36 ] or iso -alkyl groups [ 31 ] have been used to investigate their steric influence on melting point, complexation and solubility of the fused salt in Zn/Br 2 -electrolytes.…”

Energy storage mechanism, advancement, challenges, and perspectives on vivid manganese redox couples

“…This issue can be minimized by employing bromine capturing agents (BCA) such as 1-ethylpyridinium bromide, 1-alkylpyridin-1-ium bromides, and 1-alkyl-3-methylimidazol-1-ium bromides to suppress the vapor pressure of bromine. [49][50][51] Yet, the strong interaction between BCA and anionic groups in the proton exchange membrane decreases the proton conductivity as it reduces the voltage efficiency of the system. Moreover, crossover of Br À /Br 3 À species results in the degradation of the hydrogen oxidation/evaluation catalyst.…”

Reversible solid bromine complexation into Ti3C2Tx MXene carriers: a highly active electrode for bromine-based flow batteries with ultralow self-discharge

“…14,15 However, the formation of the oily polybromide phase lowers the electrolyte conductivity and uniformity, deteriorating the reaction kinetics of the Br 2 /Br À redox couple. [15][16][17] To address such a ''trade-off'' between inhibiting bromine diffusion and boosting reaction kinetics, our group has devoted great efforts to constructing highly electrochemically active electrodes with high bromine entrapping/retention capacity. 8,18,19 In particular, such electrode materials can play the same roles as BCAs, helping in constructing BCA-free Br-FBs with low self-discharge, high power density and long lifespan.…”