DISSOCIATION OF THE WATER MOLECULE
Farrah Day, October 2010
Not surprisingly there is more than one way of dissociating the water molecule. However, dissociation of the water molecule does not necessarily lead to the evolution of hydrogen and oxygen gases.
Only when the water molecule fractures cleanly into atomic hydrogen and atomic oxygen will gases be immediately evolved. However, under most circumstances the water molecule cleaves into ions of H+ and OH-. When the water molecule dissociates into two ionic species, for gases to be produced, these ionic species need a charge exchange medium whereby they can drop off and collect charges in order to become atoms.
I’ve seen on numerous occasions that some self-appointed, so-called experts in the field now demean Faraday’s Laws of Electrolysis as out-dated and irrelevant. How ridiculous such accusations are. All this does is emphasise their total lack of understanding of Faraday’s Laws of Electrolysis, and indeed their general level of ignorance on the subject.
Faraday’s Laws of Electrolysis are not difficult to understand, and anyone applying themselves to it will quickly understand why these laws are as valid now as they were when Faraday first described them. People who casually dismiss these laws are clearly uneducated and/or ignorant of the facts, and as such are not people who should be trusted or taken seriously.
The term over-Faraday is often employed to situations whereby it would seem that more gases are being produced for a given power than allowed for by Faraday’s laws. Because of the term over-Faraday, many people also seem to think that this itself invalidates Faraday’s laws, making them obsolete. It of course does not.
Faraday’s Laws of Electrolysis take into account every ion/electron reaction at the electrodes, which is why the electroplating industry can accurately determine exactly how much current will have to pass through an electrolytic solution for any given amount of deposited product. However it must be borne in mind that side reactions can occur in a standard electrolyser, and as these reactions also abide by Faraday’s Laws, they will to a lesser or greater degree have an impact on the volume of gas evolving. That is, side reactions such as iron in the electrodes reacting with oxygen to form an oxide will accordingly reduce the volume of oxygen evolving as gas.
Faraday was using dc current, plain and simple, and easy from a measurement point of view. Start pulsing dc, and measurement gets a little more difficult because not only does this ask a lot more of the measuring equipment and/or involve some additional calculation, but other elements of dissociation can come into play.
With a pure dc current drawn through an electrolytic solution, then the product or products (in the case of water: hydrogen and oxygen) is proportional to that current. The more current, the more product/s. Calculations are relatively easy and straight forward.
I’ve also seen it written that any voltage above the required voltage necessary to induce electrolysis does nothing but create heat. This of course is nonsense. Over voltage may reduce overall efficiency of the electrolyser due to the V x I = W of ohms law, but by the very same law also states V/R = I. In other words increasing the voltage will of course increase the current and so result in more product/s.
The theoretical minimum voltage to initiate Faraday electrolysis of water is 1.23 volts, but even this figure is temperature specific (around 18 deg. C). Raise or lower the temperature of the electrolytic solution and this optimum voltage figure changes accordingly. In reality there is also an over voltage potential at the electrodes that has to be overcome as well as the resistance of the electrolytic solution itself, and so typically 2 – 2.5 volts minimum is required. As inert electrodes go, platinum electrodes are the most efficient, requiring minimum over-voltage potential, but not only are they very expensive, they are also hard to come by. This is why stainless steel is generally the electrode metal of choice for electrolyser builders - be they businesses or just water fuel enthusiasts experimenting in a shed.
Faraday’s Laws are beautifully simple and extremely elegant, but they do not apply to all situations, which is where problems and confusion often stem from. Faraday’s Laws of Electrolysis are in evidence when ionic species are the current carriers within a solution and when there are charge exchange mediums present (ie, electrodes in contact with the electrolytic solution). In cases where water is caused to dissociate and evolve as hydrogen and oxygen through other means, such as plasma arcs, ultrasonic cavitation and electromagnetic radiation, when there are no charge exchange mediums present, then Faraday’s Laws cannot reliably be applied.
However, so tried and trusted are Faraday’s Laws, that they are always used as a baseline from which to judge other forms of dissociation of the water molecule.
Complications arise when people try to ascertain how much power it will take to produce a given volume of gas, because voltage then comes into play, but of course does not itself feature in Faraday’s Laws of Electrolysis.
Under ideal conditions of voltage and temperature and assuming 100% efficiency, implementing Faraday’s Law will require 3.658kW/hr to dissociate 1 litre of water into its component gases.
At STP, this will produce 1,358 litres of hydrogen and 679 litres of oxygen.
Emphasis here on STP, which hints at yet another complication. Hot gas expands and so has greater volume at equivalent pressure than when cold. So this is yet another factor that can provide very misleading results if not taken into consideration. As a reliable guideline, the difference in volume of a gas (any gas) at 0 deg, C and 100 deg. C is 36%. That is 1 litre of gas at 0 deg. C, will become 1.36 litres of gas at 100 deg. C, at equal pressures.
And of course something I never even see considered when people are measuring gas output is the water vapour content. People forget that water vapour is a gas that will be present along with the hydroxyl mix.
Yet further complications arise when the current is made to pulse and/or more than one method of dissociation is occurring within an electrolytic cell – the latter of which may be occurring completely unbeknown to the electrolyser builder/operator.
It should now be very clear to all that there are many factors to be taken into consideration when trying to determine electrolyser efficiencies, and indeed many possible areas for mistakes, miscalculations and misreading or misinterpretation of results.
Sadly, most amateur Water Fuel enthusiasts completely neglect to consider any of the above-mentioned factors which in itself makes way for wildly optimistic results and often even wilder claims.
To be continued…