Electrochemical Cell

An electrochemical cell is a device that interconverts chemical energy and electrical energy, built from two separate electrodes each in contact with an electrolyte solution. Every electrochemical cell falls into one of exactly two categories, distinguished by which direction that energy conversion runs:

1. Galvanic cell (voltaic cell). A spontaneous chemical reaction inside the cell generates an electric current — chemical energy is converted into electrical energy. This is exactly what is commonly called a battery, and it is the type of cell examined for most of this chapter (the Daniel cell, batteries, and fuel cells are all galvanic cells).
2. Electrolytic cell. An electric current supplied from an external source drives a chemical reaction that would not occur on its own — electrical energy is converted into chemical energy. Electrolysis of molten sodium chloride, covered later in this chapter, is the representative example. …