Zinc Electrodes for Acidic Neutral Primaries

The classical Ledanche cell uses zinc sheet formed into a cylindrical can serving simultaneously as the anode and as the cell container (ABICI). The cathode is a mixture of Mn02 and graphite wrapped into a piece of separator and contacted by a central carbon rod. The can dissolves slowly when the cell is not in use and faster when the cell delivers electrical energy. 

The reaction following the primary electrochemical zinc dissolution (Equation 8.18) leads, in the case of an ammonium chloride electrolyte, to a zinc diammine cation  

If aqueous zinc chloride solution serves as electrolyte ( heavy duty types), the hydrate of a basic zinc chloride is formed instead of the product in Equation 8.19  

The construction of the anode (sheet, cell container) is responsible for the two major problems  

The corrosion reactions may be slowed down by using zinc alloys (with lead and cadmium also improving the mechanical properties of zinc to simplify the production process) instead of the pure metal or by amalgamating the inner surface of the can by adding a small amount of a mercury compound to the electrolyte. 

Other ( leakproof) cells use an additional steel can on the outside to prevent any electrolyte loss caused by perforation of the inner zinc beaker when the cell is exhau.sted. 

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It is so universally applied that it may be found in combination with metal oxide cathodes (e.g., HgO, AgO, NiOOH, Mn02), with catalytically active oxygen electrodes, and with inert cathodes using aqueous halide or ferricyanide solutions as active materials ("zinc-flow" or "redox" batteries). The cell (battery) sizes vary from small button cells for hearing aids or watches up to kilowatt-hour modules for electric vehicles (electrotraction). Primary and storage batteries exist in all categories except that of flow-batteries, where only storage types are found. Acidic, neutral, and alkaline electrolytes are used as well. The (simplified) half-cell reaction for the zinc electrode is the same in all electrolytes ... 

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