Leclanché cell

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A 1919 illustration of a Leclanche cell.
A 1919 illustration of a Leclanche cell.

Georges Leclanché invented and patented in 1866 his battery, the Leclanché cell. It contained a conducting solution (electrolyte) of ammonium chloride, a cathode (positive terminal) of manganese dioxide, and an anode (negative terminal) of zinc. Leclanche battery was a copy of the earth battery.[1]

Contents

[edit] Construction

In Leclanché's original cell the cathode, which consisted of crushed manganese dioxide, was packed into a porous pot, and a carbon rod was inserted to act as an electrode. The anode, which was a zinc rod, was then immersed along with the pot in a solution of ammonium chloride. The liquid solution acted as the electrolyte, permeating through the porous cup to make contact with the cathode material.

[edit] Chemistry

The chemical process which produces electricity in a Leclanché cell begins when zinc atoms on the surface of the anode oxidize, ie they give up both their electrons to become positively-charged ions. As the zinc ions move away from the anode, leaving their electrons on its surface, the anode becomes more negatively charged than the cathode. When the cell is connected in an external electrical circuit, the excess electrons on the zinc anode flow through the circuit to the carbon rod, the movement of electrons forming an electrical current.

When the electrons enter the rod, they combine with molecules of manganese dioxide and molecules of water, which react with each other to produce manganese oxide and negatively charged hydroxide ions. This is accompanied by a secondary reaction in which the negative hydroxide ions react with positive ammonium ions in the ammonium chloride electrolyte to produce molecules of ammonia and water.

\mathrm{Zn(s)} + 2 \mathrm{MnO_2(s)} + 2 \mathrm{NH_4Cl(aq)} \rightarrow \mathrm{ZnCl_2} + \mathrm{Mn_2O_3(s)} + 2 \mathrm{NH_3(aq)} + \mathrm{H_2O}

[edit] Usage

The electromotive force (emf) produced by a Leclanche cell is typically around 1.5 volts with a resistance of several ohms where a porous pot is used. It saw extensive usage in telegraphy, signalling and electric bells and similar applications where intermittent current was required and it was desirable that a battery should require little maintenance.

The Leclanché battery (or "wet cell" as it was referred to) was the forerunner of the modern dry cell zinc-carbon battery.

[edit] References

  1. ^ The Electrical Review, 1892. Page 68.
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