published on 7 January 2009 in energy

Hydrogen vehicles

Hydrogen from water
One of the main problems with the use of hydrogen as vehicle fuel, a system that would eliminate pollution and CO2 emissions in trucks and cars, is the difficulty in storing this gas in amounts sufficient to allow the vehicle to have a decent autonomy.
Jerry Woodwall, professor of Chemistry at Purdue University in Indiana, United States, apparently has found a solution: fill the tank with water and add some special tablets made of aluminum and other chemical elements. These tablets, reacting with water, will be able to produce hydrogen for a long enough time before having to stop to refuel.
The problem
Hydrogen is a very light gas, which escapes easily and requires very low temperatures to become liquid.  Other storage systems, such as forcing hydrogen through the crystal lattice of particular substances, are being experimented, but they are expensive, heavy and difficult to use.
It is a shame, because hydrogen could be the solution to make our city traffic clean.
A car that runs on hydrogen doesn’t emit any kind of polluting fumes and besides, hydrogen can be used both in modern fuel cell engines which work according to the battery principle as well as in normal combustion engines. This is very important because it means that introducing hydrogen as fuel wouldn’t force everybody to buy a new car.

Woodall’s solution
Nature has already given us a hydrogen storage solution which is cheap and simple: water. In fact, a kilo of water contains about 100 gramms of hydrogen.
But how can we separate this gas from the oxygen in the water in a car’s tank?
Woodwall’s idea is to put aluminum in the water. Aluminum has a real hunger for oxygen, so it is able to break away this gas from the water molecule thus freeing the hydrogen. The problem is that aluminum covers immediately with an oxide layer, alumina, which keeps oxidation from occuring within the metal. We have known now for a long time that to keep this phenomenon from happening we can use a special liquid alloy made up by indium, gallium and stannum which continuously breaks down  the alumina layer so that the aluminum will react with the water’s oxygen, setting free large quantities of hydrogen.
But how can we apply this system to the tanks of millions of cars, considering also that indium and gallium are rare and expensive metals?
After many attempts, Woodhall was able to create, through a slow cooling process, a new aluminum alloy (95%) + indium-gallium-stannum (5%), which appears as a homogeneous solid versus a double state system. Tablets of this new alloy added to the water react quickly transforming all the aluminum into alumina and releasing all the hydrogen contained in the water molecules involved in the reaction. The stannum-indium-gallium alloy remains unaltered.

According to Woodall, basically the whole fuel cycle  should work the following way: a new car with a hydrogen powered engine (fuel cell electric or normal combustion which burns gasses in the cylinders) goes to the gas station, fills the tank with water and adds a certain number of tablets made of the new 95-5 alloy. These react and produce the necessary hydrogen for the car to go. When all the water has been transformed and the car is on reserve, the motorist returns to the gas station, where the spent solution is removed from the tank and replaced with new water and 95-5 alloy tablets. The spent solution containing alumina and the other metals is then sent to a recycling center where new aluminum is extracted consuming only one third of the energy necessary to extract this metal from its original mineral while indium, gallium and stannum get completely recycled and used once again to make new 95-5 alloy tablets.
Basically, the only energy used to make a car go is the one which is necessary for the production or recycling of the aluminum alloy, which can also come from renewable sources, such as sun or wind. The metal is almost 100% recyclable, so there is no consumption of new resources. According to Woodall, the recycling cycle of his tablets would be so cheap and efficient that, beyond 60 recycling cycles, the energetic consumption of hydrogen powered vehicles, would be less than the one of similar ones running on hydrogen obtained from water electrolysis or from methane processing as is done nowadays.

Written by Videoscienza

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