Zinc bromide in aqueous solutions of ionic liquid bromide salts: the interplay between complexation and electrochemistry

Voltammetric studies of ZnBr2 (50 mM) in aqueous equimolar solutions of ionic liquid bromide salts (1-alkyl-1-methylpyrrolidinium bromide, [C(n)MPyrr], and tetraalkylammonium bromide, [N-n,N-n,N-n,N-n]Br, 50 mM, where n = 2, 4 or 6) are reported. A simple increase in alkyl chain length of the cation of the bromide salt greatly altered the mechanism of zinc deposition as a result of the complexation of bromozincate anions. The structures of two such bromozincates were isolated and their structures determined by single-crystal X-ray diffraction. These findings provide an additional strategic basis for the design of alternate bromine sequestering agents for aqueous zinc bromide flow cells.