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Dry-Cell Battery

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The most common type of battery used today is the "dry cell" battery. There are many different types of batteries ranging from the relatively large "flashlight" batteries to the minaturized versions used for wristwatches or calculators. Although they vary widely in composition and form, they all work on the sample principle. A "dry-cell" battery is essentially comprised of a metal electrode or graphite rod (elemental carbon) surrounded by a moist electrolyte paste enclosed in a metal cylinder as shown below.

In the most common type of dry cell battery, the cathode is composed of a form of elemental carbon called graphite, which serves as a solid support for the reduction half-reaction. In an acidic dry cell, the reduction reaction occurs within the moist paste comprised of ammonium chloride (NH4Cl) and manganese dioxide (MnO2):


The alkaline dry cell lasts much longer as the zinc anode corrodes less rapidly under basic conditons than under acidic conditions.
Other types of dry cell batteries are the silver battery in which silver metal serves as an inert cathode to support the reduction of silver oxide (Ag2O) and the oxidation of zinc (anode) in a basic medium. The type of battery commonly used for calculators is the mercury cell. In this type of battery, HgO serves as the oxidizing agent (cathode) in a basic medium, while zinc metal serves as the anode. Another type of battery is the nickel/cadmium battery, in which cadmium metal serves as the anode and nickel oxide serves as the cathode in an alkaline medium. Unlike the other types of dry cells described above, the nickel/cadmium cell can be recharged like the lead-acid battery.

Dry Cell Battery

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Batteries

A battery is a device consisting of a galvanic cell or a series of combined galvanic cells that can be used to derive a direct electric current at a constant voltage. Even though, battery is galvanic in nature, it has one advantage; it is self-contained and requires no salt bridge. Here few common batteries are discussed.

The Dry Cell Battery

This is a most common dry cell battery without any fluid component and is known as a Leclanche’ cell that is used in flashlights, toys, transistor radios.

The Mercury Battery

The mercury battery is more expensive than the common dry cell and mainly used in electronic and medical devices, such as, hearing aids, electronic watches, and pacemakers. This battery consists of a stainless steal container with zinc amalgamated with mercury (Zn(Hg)) as anode, which is in contact with a strong alkaline electrolyte of zinc oxide and mercury(II) oxide.

The Lead Storage Battery

The lead storage battery is commonly used in automobiles consists of identical cells connected in series. Each cell provides 2V and when they are connected in series, their voltages are additive. Most automobile batteries contain six cells to give a total of 12V. But batteries with 6V, 24 V, and 32V are also available.
Each cell has anode and cathode. Anode consisting of set of lead (Pb(s)) plates and cathode composed of a set of lead plates covered with lead oxide (PbO2). Both electrodes are immersed in an electrolyte, a mixture of water and highly concentrated solution of sulfuric acid (H2SO4 (aq)). Schematic diagram is shown below.

Fuel Cells

The galvanic cells discussed above are wonderful but produce power for a limited time because electrolytes are eventually exhausted. On the other hand, fossil fuels, our major source of energy, are very inefficient; the most modern electric plants can harness only about 35 - 40% of the chemical energy in coal, natural gas or oil. The rest of the energy is lost to the surrounding in the form of heat. Considering these facts, the fuel cells become more attractive.