Electrochemical processes as sources of energy

Electrical energy may be produced through the operation of a chemical reaction taking place in a galvanic cell. The earliest, most rudimentary form of galvanic cell consisted of alternate sheets of copper and zinc separated by wet cloth. This arrangement subsequently gave rise, in a rather different form, to the Daniell cell. 

There are essentially three types of galvanic cell, viz.  

These are based upon reactions which are not reversible so that recharging is out of the question and once the cell reaction has proceeded to completion, the cell is discarded. 

Such cells are based upon almost reversible electrode processes. All processes occurring during their discharge while used as a source of e.m.f. may to a large extent be reversed in the recharging process. The overall efficiency of the recharging reaction may be significantly reduced by side reactions. 

In fuel cells an attempt is made to make the fullest possible use of the free energy of reactions, such as the combustion of fuels, to produce electrical energy. Processes are chosen which occur as nearly reversible as possible in order to obtain the maximum useful proportion of AG. The mode of operation of fuel cells is fundamentally different from that of batteries. While batteries store electrical energy, fuel cells convert energy obtainable from chemical processes directly into electricity. 

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