Zinc-bromine accumulator

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A zinc-bromine battery ( zinc-bromine battery for short ) is an embodiment of a redox flow battery in which the electrodes , when charged, consist of the elements bromine and zinc .

Chemical processes

The following chemical processes take place during discharge:

Positive pole:

Negative pole:

(When loading, the processes run in the opposite direction.)

The overall reaction:

To the right the battery is discharged, to the left it is charged.

The theoretical potential difference is 1.83  V .

The chemical processes run somewhat differently in practice, especially with larger current consumption, the collapse of the hydrogen protective voltage leads to the formation of hydrogen on the zinc electrode due to the low pH value of 1.5-2, see Kipp's apparatus . Escaping hydrogen causes the pH value of the electrolyte to rise and can therefore destroy the separator in a relatively short time, as zinc hydroxide is formed and this closes the pores. Normally it is not possible to recombine the gaseous hydrogen with bromine to form hydrogen bromide.

In addition, it has been shown in practice that dendrite growth occurs in poorly perfused areas on the zinc electrode and this leads to an internal cell fire. The accumulator would then be irretrievably destroyed.
In the event of such a cell fire, toxic bromine vapors can still be released.