Zinc-bromine cell

Various materials have been used as separators in zinc—bromine cells. Ideally a material is needed which allows the transport of zinc and bromide ions but does not allow the transport of aqueous bromine, polybromide ions, or complex phase structures. Ion selective membranes are more efficient at blocking transport then nonselective membranes.These membranes, however, are more expensive, less durable, and more difficult to handle then microporous membranes (e.g., Daramic membranes).The use of ion selective membranes can also produce problems with the balance of water between the positive and negative electrolyte flow loops. Thus, battery developers have only used nonselective microporous materials for the separator. 

Nafion membranes have been used as separators in the hydrogen-chlorine cell/ " hydrogen-bromine cell, and zinc-bromine cell because of their excellent chemical inertness in these aggressive environments. The function of the separator in these cells, similar to that in a water electrolyzer, is the separation of the molecular species, such as hydrogen, chlorine, bromine, and metallic zinc, which cause self-discharge and efficiency loss when they migrate across the separator. 

The Nafion membrane has been used as a separator in both the hydrogen-halogen cell (45,50) and in the zinc-bromine cell (38) because Nafion is a highly stable perfluorinated material which is not affected by strong acids and halogen. 

The overvoltage of the hydrogen halogen cell and the zinc-bromine cell is mainly contributed by the membrane resistivity, and this resistivity is a strong function of the electrolyte content in the membrane. It is clear that the membrane hysteresis effect will influence the cell performance. 

In the zinc/bromine cell, the halogen is stored in the electrolyte as a polybromide (mainly Bra ) and hence a separator is essential Nafion cation exchange membrane has again been used. The electrolyte is aqueous zinc bromide with tetraalkyl-ammonium bromide to aid the bromine complex formation. 

Engineering of the chlorine battery is well advanced but zinc/bromine cells exist only as small laboratory modules. 

Cedzynska K (1995) Properties of modified electrol3de for zinc-bromine cells. Electrochim Acta 40 971-976. doi 10.1016/0013-4686(94)00372-8... 

Cathro KJ, Cedzynska K, Constable DC, Hoobin PM (1986) Selection of quaternary ammonium bromides for use in zinc/bromine cells. J Power Sources 18 349-370. doi 10.1016/ 0378-7753(86)80091-X... 

Cathro KJ (1988) Performance of zinc/bromine cells having a propionitrile electrolyte. J Power Sources 23 365-383. doi 10.1016/0378-7753(88)80081-8... 

Cedzynska K (1989) Some properties of zinc-bromine cell electrolytes containing symmetrical ammonium bromides. Electrochim Acta 34 1439-1442. doi 10.1016/0013-4686(89)87185-3... 

K. Cedzynska, Properties of Modified Electrolyte for Zinc-Bromine Cells, Electrochimica Acta, 40(8) 971-976 (1995). 

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