By providing energy from a battery, water (H2O) can be dissociated into the diatomic molecules of hydrogen (H2) and oxygen (O2). This process is a good example of the the application of the four thermodynamic potentials.The electrolysis of one mole of water produces a mole of hydrogen gas and a half-mole of oxygen gas in their normal diatomic forms.
Hydrogen electrolysis is the process of spitting water into Hydrogen gas and Oxygen gas. The Hydrogen gas can then be used as fuel either by being burnt in an engine or reacted in a fuel cell. This is the process that so-called water powered cars rely on for their energy. No car can use water as a fuel, but a car can be made to run only on Hydrogen, meaning that its exhaust gas will be just water vapor.
As with all electrolysis, an electric current is pumped into a circuit. Instead of a circuit that is completely made of wires, the reactions of the chemicals in the solution being electrolyzed both provide and consume the electrons. This makes the equivalent of a complete wire loop and allows current to be supplied to the liquid continuously. The basic setup for electrolysis of water is shown to the right. This setup is fundamental to all electrolysis reactions.
The rods inserted in the water are called electrodes. The one where electrons come out is called the anode and the one where the electrons go in is called the cathode. The reactions that occur at these electrodes are different and this difference is caused by the removal or supply of electrons.
As is the case for other oxidation reduction reaction, the reaction where electrons are removed is called an oxidation reaction, and the reaction where electrons are supplied is called a reduction reaction. Using this knowledge, we can add more detail to the previous diagram: The electrolysis of one mole of water produces a mole of hydrogen gas and a half-mole of oxygen gas in their normal diatomic forms.