An electrochemical cell is a device that generates electrical energy from chemical reactions. Electrical energy can also be applied to these cells to cause chemical reactions to occur. Electrochemical cells that generate an electric current are called voltaic or galvanic cells and those that generate chemical reactions, via electrolysis for example, are called electrolytic cells.
A modern electrolytic cell consisting of two half reactions, two electrodes, a salt bridge, voltmeter, and a battery.
Circuit diagram of a primary cell showing difference in cell potential, and flow of electrons through a resistor.
Lead acid car battery (secondary cell)
Redox is a type of chemical reaction in which the oxidation states of a reactant change. Oxidation is the loss of electrons or an increase in the oxidation state, while reduction is the gain of electrons or a decrease in the oxidation state.
Oxides, such as iron(III) oxide or rust, which consists of hydrated iron(III) oxides Fe2O3·nH2O and iron(III) oxide-hydroxide (FeO(OH), Fe(OH)3), form when oxygen combines with other elements.
Iron rusting in pyrite cubes
Enzymatic browning is an example of a redox reaction that takes place in most fruits and vegetables.
Blast furnaces of Třinec Iron and Steel Works, Czech Republic