by Shahid Mansoor

Created on: March 20, 2007   Last Updated: April 23, 2007

The electrolysis of water is a simple method of producing hydrogen (In practice a saltwater solution increases the reaction intensity). A low voltage DC (direct current) is run through the water by using cathode and anode plates. Typically, the cathode is made of platinum when producing hydrogen for storage. Oxygen forms at the anode and hydrogen forms at cathode. The hydrogen produced by this process has less energy content that the energy gone in to produce hydrogen due the efficiency of the process. Average efficiency is around 50-70% and the theoretical maximum efficiency can be between 80-94%.

Gas Production Formulas:

The following calculations can be used to work out the output of hydrogen in 1 hour. First measure power input at the electrolyser terminals. Multiply the voltage with amps to get the power input in watts. For instance if the electrolyser draws 5v at 20amp then this would be 100 watts of power being used by the electrolyser.

It is known that 1 watt per second equals 1 joule per second. Thus, 100 watts of power usage would be equivalent to 100 joules per second. There are 3600 seconds in one hour, so simply multiply 100 times 3600 seconds. This would be 360000 joules per hour (360 kj).

One litre of water has 1358.3 litres of hydrogen and 679.15 litres of oxygen. There is a potential energy of 13,170.9 kj in one litre of water so it would require the same amount of energy to disassociate one litre of water. So we divide 13,170.9 kj by 360 kj which indicates that it would take around 36.6 hours to electrolyse 1 litre of water and produce 1358.3 litres of hydrogen and 679.15 litres of oxygen.

To find out how many litres of hydrogen are produced in 1 hour simply divide 1358.3 by 36.6 hours. This will be the litres of produced in 1 hour, in this case it would be 37.11 litres of hydrogen per hour.

You can clearly see that one electrolyser consuming 100 watts will produce 37.11 litres of hydrogen in 1 hour (based on 100 % efficiency). More electrolysers can be added, each consuming 100 watts if the hydrogen needs to be produced at a faster rate.

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