Zinc-chlorine cells

Zinc chloride cell Zinc-chlorine cell Zinc chromate... 

In the zinc/chlorine cell, the chlorine is stored as chlorine hydrate, Cl2 xH20 (x = 6—10), which precipitates as a solid below 9.6°C. During charge the electrolyte, aqueous zinc chloride, is cooled in a reservoir, while during discharge the reservoir is heated under controlled conditions. The cell itself, however, can be simple the electrodes are graphite and can operate without catalyst and the cell can be constructed from PVC without a separator. There remain some problems with the morphology of zinc deposits. 

Other alkaline primary cells couple zinc with oxides of mercury or silver and some even use atmospheric oxygen (zinc—air cell). Frequendy, zinc powder is used in the fabrication of batteries because of its high surface area. Secondary (rechargeable) cells with zinc anodes under development are the alkaline zinc—nickel oxide and zinc—chlorine (see Batteries). 

Fig. 9.20 Comb-type bipolar electrodes for zinc-chlorine batteries (a) bipolar stack (b) unit cell...

It is immediately apparent that the Daniell cell differs from the zinc-chlorine battery in that the electrode materials (i.e., zinc and copper) of the former are both metals that normally exhibit a tendency to lose electrons. If the Daniell cell is to function as a battery, both metals cannot lose electrons—one must lose and the other must gain electrons. In this particular case, the issue can be decided, qualitatively at least, in terms of the order of activity of the metals. From Table 11.1, it should be recalled that zinc is much more active chemically than copper hence zinc might be expected to lose electrons more readily than copper if the metals are in contact with solutions of their ions at the same concentration. It may be inferred correctly that the reactions that occur when the Daniell cell serves as a source of electrical energy are as follows ... 

Any consideration of the requirements to be fulfilled in the construction of battery cells should recognize first that the substances used as electrodes may be, but need not be, produced by electrolysis. In the earlier discussion of the zinc-chlorine battery, both of the substances involved at the two terminals were considered to be the products of a previously conducted electrolysis. However, the zinc-chlorine battery could just as well have been constructed by the use of zinc and chlorine produced by entirely nonelectrolytic methods. You should recall that, in connection with the description of the Daniell cell, no specifications were made with regard to the origin of any of the chemicals involved. This freedom to select suitable materials regardless of their origin or past history follows from the fact that the changes that occur during... 

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. 

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

Jome J, Kim JT, Kralik D (1979) The zinc-chlorine battery half-cell overpotential measurements. J Appl Electrochem 9 573-579. doi 10.1007/BF00610944... 

Nickel-zinc storage cells Nickel-hydrogen storage cells Chlorine-zince storage cells Sulfur-sodium storage cells Iron sulfide-lithium storage cells Zinc-air cells Iron-air storage cells... 

Fig. 4. Schematic of the system with chlorine-zinc storage cells.

In a zinc/chlorine RFB, the theoretical cell voltage of 2.12 V is defined according to the following reactions ... 

Because of serious environmental hazards associated with the evolution of toxic chlorine gas, the zinc/chlorine battery is unsuitable for practical use, even with a higher cell voltage than that of the zinc/bromine system. 

In zinc/chlorine and zinc/bromine batteries, the active material is partially stored outside the electrodes in separate tanks which in parallel supply all cells of the battery. 

The zinc/chlorine battery was a predecessor of the zinc/bromine battery. It had been developed in the 1960s and 1970s for vehicle application (cf., e.g. Ref. 76, p. 302). It is based on the cell reaction... 

Gas-activated Batteries. The gas-activated batteries were attractive because their activation was potentially simpler and more positive than liquid or heat activation. The ammonia vapor-activated (AVA) battery was representative of a system in which the gas served to form the electrolyte. (Solids such as ammonium thiocyanate will absorb ammonia rapidly to form electrolyte solutions of high conductivity.) In practice, ammonia vapor activation was found to be slow and nonuniform, and the development of the ammonia battery was directed to liquid ammonia activation which, in turn, was found to be inferior to newer developments. The chlorine-depolarized zinc/chlorine battery was representative of the gas depolarizer system. This battery used a zinc anode, a salt electrolyte, and chlorine, which was introduced into the cell, at the time of use, as the active cathode material. The battery was designed for very high rate discharge ranging from 1 to 5 min, but its poor shelf life while inactivated limited further development and use. 

A wide range of cell-based biosensors (with bacteria, yeast, algae, and tissue culture cells) were reported also in the literature for potential environmental applications. Genetically modified microorganisms capable to detect the presence of toxic metals like lead, mercury or zinc, chlorinated compounds, organic peroxides, nitrate, or ammonia were used in the development of biosensors. 

Figure 6.17 Production of an emf in a cell consisting of a zinc electrode and a chlorine electrode in zinc chloride solution.

Reversible operation of the cell requires that no other process occurs in the cell than that connected with the current flow. An electrochemical process that need not be always connected with the passage of current is the dissolution of a metal in an acid (e.g. zinc in sulphuric acid in the Volta cell) or the dissolution of a gas in an electrolyte solution (e.g. in a cell consisting of hydrogen and chlorine electrodes, hydrogen and chlorine are dissolved... 

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