The Electrolysis of water in Hydrogen Hybrid Cars happens when an
electric current passes through the water causing the water (H2O) to
break down into its two basic elements, oxygen (O2) and hydrogen gas
(H2). It's interesting to note that Industrial applications don't use
this method of hydrogen production much since they can do it more
affordably by getting it out of fossil fuels.
The way this works
in Hydrogen Hybrid Cars is by taking an electrical power source and
connecting it to two electrodes, or plates, (or multiples of two)
usually made out of some kind of stable metal like aluminum or stainless
steel, then putting them into the water. If this cell is made correctly
then Hydrogen will form on the cathode (metal plate that's negatively
charged), and oxygen will form on the anode (metal plate that's
positively charged). Since there's two hydrogen molecules to every one
oxygen, molecule in water the amount of hydrogen produced is twice that
of oxygen and both are in proportion to the electrical charge that runs
through the water.