MEP (N-methyl-N-ethylpyrrolidinium bromide, 99.5%) as Bromine Complexing Agent for Zn-Br2 Redox Flow Battery, 50 g/bottle, CZBRFBBCAMEP

In Zinc-Bromine (Zn-Br2) batteries, MEP (N-methyl-N-methylpyrrolidinium bromide, or called N-Ethyl-N-methylpyrrolidinium bromide) is the industry-standard Bromine Complexing Agent (BCA). It is a quaternary ammonium salt used to manage the hazardous and highly reactive elemental bromine generated during the charging process. The roles of MEP in Zn-Br2 Batteries are mainly displayed as below: (1) Self-Discharge: Free Br2 can diffuse through the separator to the zinc anode, where it reacts directly with the metallic zinc, causing rapid energy loss. (2) Safety Hazards: Br2 has a high vapor pressure (13 mbar at 20°C); it easily evaporates into a toxic red-brown gas.

When Br2 is produced at the cathode during charge, it immediately reacts with the MEP molecules in the electrolyte to form polybromides (like [MEP]Br3 or [MEP]Br5). These complexes are: Immiscible: They form a dense, oily red liquid phase that sinks to the bottom of the electrolyte tank. Stable: They significantly reduce the vapor pressure of the bromine, making the battery much safer. Reversible: During discharge, the oily phase is pumped back to the electrode, where the bromine is released and reduced back to bromide ions (Br-).

Part Number	CZBRFBBCAMEP (C-ZBRFB-BCAMEP)
Appearance	Off-white powder (or light yellow)
Purity	>99.5%
CAS	69227-51-6
Chemical Formula & Structure	C7H16BrN
Molecular Weight	194.11
Package Grade	50 g/bottle

References

(1）M. Zhao, et al., A Choline-Based Antifreezing Complexing Agent with Selective Compatibility for Zn–Br2 Flow Batteries, Small, 2024, 20, 2307627. 

(2) Y. Liu, et al., Synergistic Electrolyte Design for High-Performance Static Zinc–Bromine Batteries, ACS Energy Lett. 2025, 10, 11, 5809–5824.