| In his Ile Mystérieuse, Jules Verne wrote that water would one day be used as a fuel ! « ..hydrogen and oxygen, which constitute air, used separately or together, will provide an inexhaustible source of heat and light »
Hydrogen, a very special animal!
Imagine the simplest and lightest element that the universe can contain; an element which does not exist in nature, but which has to be produced and whose main attribute is its capacity to produce energy; an atom, either in its simple form of one electron and one proton, or present in water, sugar, proteins and hydrocarbons, storage of which is one of the major challenges of our century; there, in a nutshell, you have hydrogen!
The principal source of energy in the future? It might indeed be
…but provided we manage to store it! Hydrogen can go up in flames or explode in contact with the air, so it has to be handled and used with a lot of care. Chemists and physicists all over the world are working on the question. If we are to face up to the energy issues resulting from diminishing fossil resources (oil gas, coal) and the need for action posed by the problems of climate change, we must diversify our methods of energy production now, if we want to hand on a sustainable planet to future generations.
Hydrogen represents an interesting option, with a double advantage: it is inexhaustible and « clean » (non-polluting). A practical example: 1kg of hydrogen liberates about 3 times more energy than 1kg of petrol. But, since hydrogen is the lightest of the elements, it occupies, for the same weight, a much bigger volume than other gases.
To produce the same energy as 1 litre of petrol, 4.6 litres of hydrogen are required under a pressure of 700 bars – a major constraint for transport and storage in either gaseous or liquid form…
A difficult problem: how to package hydrogen in a way that is usable in practice!
Scientists the world over are currently trying to find the solution: how to get the largest possible quantity of hydrogen into the smallest possible volume, in complete safety and with the fewest constraints ?
Storage as a liquid already exists. It is the form in which it is used even in the space industry, but hydrogen remains the most difficult gas to liquefy, the transformation requiring extremely low temperatures (-253°). It is a solution involving major expenditure of energy and therefore high costs.
Storage in gaseous form under high pressure is an attractive option, but there are many problems. Extremely light and voluminous, hydrogen must be compressed to a maximum to reduce reservoir volumes. The compression involves high cost and bottles which are too heavy.
Neither of these two techniques is really suitable for industrial or domestic applications, like running a car or making a factory work.
What then is the solution?
Low pressure storage appears to be one of the research areas attracting the most study. Still to be identified is a material capable of absorbing an enormous volume of hydrogen and then releasing it on demand, whilst providing a means of storage that is both compact and safe. Here then is what engineers dream of for storing the energy of tomorrow’s electric car, of solar power plants, etc…
Hydrides: one of the promising ideas for storing hydrogen
To make possible the use of this energy of the future, scientists are currently studying compounds which can be more easily stored, in liquid or solid form and to which hydrogen could be linked chemically. The hydrides (1) appear to meet requirements. In the course of its experimental programme, the Swiss-Norwegian team of the ESRF (European Synchrotron Radiation Facility) has devoted studies to one of them: « lithium borohydride » (LiBH4) (2). The only problem with this compound, which is available in powder form, is its stability, which makes the extraction of the hydrogen difficult after storage.
The team at the Grenoble Synchrotron has gone further, postulating a way of storing hydrogen, using LiBH4 (2) in which the hydrogen atoms are so close to one another that the compound becomes unstable… A fault which proves to be an unexpected quality…It holds out promise of easier hydrogen extraction!
A very encouraging discovery, but the research must continue: whilst we now know that this super hydrogen sponge exists, we have to learn how to understand and control it in practical applications.
|
|
|
|
(1) Metals and hydrogen
A hydride is a chemical compound of hydrogen with other elements. In the early days, the term «hydride » was strictly reserved for compounds containing metals, but the definition has been widened to include all compounds where hydrogen has a direct bond with another element. A lot of metals absorb hydrogen in an irreversible way, forming a metallic hydride. This latter makes materials brittle, with sometimes disastrous consequences for their mechanical properties (cracking of steel, reinforced concrete, etc.). But what interests us here is a positive aspect: the storage of hydrogen. Metals are often crystalline materials with their atoms arranged in perfect order in the three spatial dimensions. Such an array contains empty spaces, which a hydrogen atom, the smallest of all atoms, can easily slip into … and even come out again! What is called the property of reversibility.
(2) Lithium borohydride(LiBH4)
Lithium borohydride (LiBH4) is a hydride existing as a powdery crystalline solid, white or grey in colour and odourless.
It contains a significant proportion of hydrogen (18% by weight).
It is most often used as a reducing agent in the preparation of organic products.
Other names used for LiBH4: Borate(1-), Tetrahydro, Lithium, Lithium borohydride, Lithium Boron Hydride.
|
|
|
|
|
|
| To find out more about hydrogen, consult the Encyclo |
|
|