Precision 500
User Manual
Page 11
2012 © Peak Scientific – Rev 2 – 07/11/12
Principle of Operation
The Peak Scientific Hydrogen Generator uses a proton exchange membrane
(PEM) that is extensively used in industrial and laboratory applications. The
reliability of this type of membrane is assured as it was originally developed for
NASA. To produce the highest purity of hydrogen that an analytical laboratory
requires, Peak Scientific employs the services of a platinum catalyst in the
electrode area.
Electrolysis of water is the best method of producing high purity hydrogen on
demand. The most important element of the generator is the electrolyser cell
where the electrolysis reaction takes place. This consists of two electrodes (an
anode and a cathode), which are separated by the ion exchange membrane.
When a continuous voltage is applied to the electrodes on the electrolyser cell,
the following reactions take place: -
At the anode (the positively charged electrode), the water molecules
loose two electrons forming an oxygen molecule and four hydrogen
ions.
Anode
2 H2O - 4e = O2 + 4 H+
The oxygen that is produced in this half of the reaction is safely vented to
atmosphere at the back of the generator. The four hydrogen ions that have
been produced then pass through the ion exchange membrane (attracted by
the negatively charged cathode) and collect four electrons reducing them to
two hydrogen molecules.
Cathode
4 H+ + 4e = 2H2
The hydrogen produced is separated from the oxygen by the ion exchange
membrane, which is impervious to molecular oxygen. Deionised water is the
raw material of the system and must have a purity of 1
µ
s/cm or better to
prevent damage to the membrane.
Failure to use this grade of deionised water will invalidate the warranty of
your generator.
The water is automatically loaded (either at power-up or periodically during
operation) and the rate, at which the water is consumed, depends on the
amount of hydrogen used - 1cc of water produces 1244cc of hydrogen. Some
electrical energy is lost as heat, which is removed from the generator by the
ventilation system.
Hydrogen is generated on demand. By maintaining the user’s preset pressure
and using this as a reference value, the generator will produce the exact
amount of hydrogen required. As soon as the demand from the consuming
application stops, then no gas is generated and the generator will maintain the
supply lines at the preset pressure.
