Electrolysis of water
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Contents |
Safety
The energy required to ignite hydrogen/air mixture is in the order of 20 uJ so it ignites very easily. The diffusion coefficient is large so it mixes fast with air and it is explosive at a wide range of mixture ratios. This means that if you are collecting any amount of hydrogen you need to be careful to avoid explosions and make sure that any accidental explosions does not cause any harm.
Recommended method
This method is safe, cheap and clean.
Electrodes
The electrodes should be high quality stainless steel plates; normal steel will be attacked by the electrolyte. Carbon rods can also be used but because of the small surface area the production rate will be low.
Electrolyte
The electrolyte is added because pure water is a bad conductor and most of the energy would be wasted as heat. The added electrolyte makes the resistance drop and a much larger current will be possible at a given voltage, resulting in far less waste heat. The most practical electrolyte is sodium hydroxide (lye) - NaOH. Potassium hydroxide - KOH will give a slight increase in efficiency but is generally not worth the trouble since sodium hydroxide is usually simpler to find.
Power supply
A high current, low voltage PSU should be used. At voltages below 1.23 V no decomposition of the water will occur. Voltages above 2.5-3 V are wasteful since the extra voltage will not cause more hydrogen to be produced, it will only generate more heat. Any extra hydrogen produced because of higher voltage is a result of the higher current. The hydrogen production is directly related to the current so to increase production rate more electrolyte should be added or the surface area/spacing of the electrodes should be improved instead of increasing the voltage. A PC power supply would be a good choice since they are cheap and capable of delivering high currents at low voltages.
Collection
Hydrogen will bubble from the negative electrode and oxygen will bubble from the positive electrode. There will be twice the amount of hydrogen than of oxygen. The gasses should always be collected in separate containers that start out filled with water so the gasses slowly replace the water. If the containers contain any amounts of air before the filling starts an explosive mixture is likely to result.
If both gasses are collected in the same container you get oxyhydrogen gas, which is very unsafe and extremely explosive. One gram of hydrogen will release 142.35 kJ of energy when burning/exploding.
