Electrochemistry is the branch of chemistry that studies the relationship between electricity and chemical reactions. It involves the movement of electrons during reactions, which can produce electrical energy or be driven by it. Common applications include batteries, fuel cells, and electrolysis, where electrical energy is used to drive chemical changes. In electrochemical cells, chemical energy is converted into electrical energy through oxidation and reduction reactions. The two main types of cells are galvanic cells, which generate electricity from spontaneous reactions, and electrolytic cells, which require an external power source to drive non-spontaneous reactions.