Effect of Bromine Complexing Agents on the Performance of Cation Exchange Membranes in Second‐Generation Vanadium Bromide Battery

Abstract

The effect of bromine complexing agents, N‐ethyl‐N‐methyl‐morpholinium bromide (MEM) and N‐ethyl‐N‐methyl‐pyrrolidinium bromide (MEP) on the performance of different perfluorinated cation exchange membranes, ChiNaf and VF11, is assessed in the G2 vanadium bromide battery (V/Br). It is noted that in the absence of MEM and MEP, the thicker ChiNaf (50 μm) membrane shows a higher energy efficiency at a current density of 20 mA cm−2. A preliminary test of ChiNaf at two different concentration ratios of MEM and MEP evaluated at 4 mA cm−2 shows that a mixture of 0.19 M MEM and 0.56 M MEP provides a slightly higher cell efficiency than the other tested compositions. However, better cell performance is obtained with the VF11 (25 μm) membrane at 4 mA cm−2 using 0.19 M MEM and 0.56 M MEP. Further studies using VF11 with a mixture of 0.19 M MEM and 0.56 M MEP at 20 mA cm−2 provide direct evidence that the addition of MEM+MEP lowers the cell performance through a reduction in voltage efficiency. The increased membrane resistance after the introduction of MEM and MEP marks the formation of an organic layer after bromine reacts with MEM and MEP and is deposited onto the membrane.

A review of electrolyte additives and impurities in vanadium redox flow batteries

“…Agents including polyethylene glycol, tetrabutylammonium bromide, N-methyl-N-ethyl pyrrolidinium bromide (MEP) and N-methyl-N-ethyl morpholinium bromide (MEM) and their mixtures were evaluated in terms of the inhibiting effect on bromide vapour production [100] . Among these, MEP and MEM can supress the Br 2 vapour effectively but will deposit an organic layer onto the membrane, thus leading to reduced conductivity of the membrane and a decline of the total energy efficiency [101,102] .…”

Nanostructured Electrocatalysts for All‐Vanadium Redox Flow Batteries

“…As for the rate of vanadium redox reactions, it is well known that the electron transfer and mass transport control the electrode reactions on the surface of the carbon‐based materials . There are commonly used carbon electrodes such as graphite felt, carbon felt, or carbon paper, which have high electrical conductivity and stability in concentric acid‐based vanadium electrolytes . The basic properties of several carbon felt electrodes have been systemically investigated for their catalytic activities .…”

A Newly Designed Modular ZnBr2 Single Cell Structure

“…The electrolyte configuration is also very important for a ZBFB system, which is related with many problems during charging, such as electrode corrosion, high self-discharge rate, zinc dendrite formation, etc. [18] According to [19], we set our ZnBr 2 solution molar concentration as 2 mol/L, which has good conductivity and lower corrosion rate, and the total volume of the electrolyte is 1 L. In order to prevent the bromine from transferring into the zinc half-cell, we chose methylethylmorpholinium bromide (MEM) as our complexing agent. Zinc bromide (ZnBr 2 ), potassium chloride (KCl) are both from NARI Technology Co., Ltd. (Nanjing, China).…”