We’ve designed RoboPlant to feature an electrolyser, powered by solar cells, which splits water into oxygen and rocket fuel. Wait, what?
That is correct – pure hydrogen is a fuel, and has been suggested as the energy medium of the future due to its high energy density, abundance (it’s the most abundant element in the universe) and the fact that it produces only water as a by-product when burned. Indeed, it has been used as a powerful rocket fuel for NASA’s space shuttles, also supplying the crew with drinking water. But could hydrogen fuel really be utilised beyond such niche applications, and be the fuel of a sustainable, emissions-free future? This week I wanted to know if there’s any warrant for all the hype about hydrogen, and if a proposed ‘hydrogen economy’ could really be achieved, so I hit the net and endeavoured to find out.
The idea of a future world powered by hydrogen is not a recent one. In his 1874 novel The Mysterious Island, the French author Jules Verne – as much a pioneer of modern science as a brilliant storyteller – had one of his characters, Harding, explain the idea when asked what mankind would do once coal reserves run out:
“But what will they burn instead of coal?” asked Pencroft
“Water,” replied Harding.
“Water!” cried Pencroft, “water as fuel for steamers and engines! water to heat water!”
“Yes, but water decomposed into its primitive elements,” replied Cyrus Harding, “and decomposed doubtless, by electricity, which will then have become a powerful and manageable force…Yes, my friends, I believe that water will one day be employed as fuel, that hydrogen and oxygen which constitute it, used singly or together, will furnish an inexhaustible source of heat and light, of an intensity of which coal is not capable. Someday the coalrooms of steamers and the tenders of locomotives will, instead of coal, be stored with these two condensed gases, which will burn in the furnaces with enormous calorific power… Water will be the coal of the future.”
(Abridged from The Mysterious Island by Jules Verne, 1874)
Leave the mysterious island and jump forward to 2013, and after nearly 140 years, there are genuine signs that Verne’s vision may finally be becoming a reality. The “inexhaustible source of heat and light” refers to the energy that is released when hydrogen is reacted with oxygen in the air. Hydrogen gas, when mixed with oxygen and ignited with a spark, causes a powerful exothermic reaction (a reaction which releases energy – an explosion, in other words), which also forms water. Technologies have been developed to harness the energy of this reaction, almost exactly as Verne prophesised. In rocket engines, the powerful explosion resulting from the combination of liquid hydrogen with compressed oxygen is enough to propel the rocket into space. In hydrogen fuel cells, energy is released when stored hydrogen reacts with oxygen in the air, and this reaction energy generates an electric current. Hydrogen powered cars are propelled by electricity from fuel cells in this way. They have already been developed and many car companies are already looking to bring them to the masses. Hydrogen cars may well be the first step to realising a hydrogen-powered transport infrastructure.
Hydrogen transport doesn’t exactly have a pristine record, however. The 1937 Hindenburg disaster, which killed 36 people, is believed to have resulted when the hydrogen-air mixture within the airship was ignited, setting fire to the outer canvas and sending it plummeting to the ground in flames. In reality however, such hydrogen-air mixtures are no more flammable than petrol, and the fate of the Hindenburg was as much thanks to the use of flammable acetate and aluminium powder covering the airship as it was thanks to hydrogen. Nevertheless, storing large quantities of hydrogen in small spaces so it can be transported and kept safely for use in, say, hydrogen-powered cars, is a technological challenge. There are numerous safety issues with some of the currently suggested techniques, including storage as compressed gas in highly pressurised tanks or as liquid in super-cooled tanks. These tanks may be liable to explode on impact or if they are exposed to too much heat, unless they are built from a very strong material. Current hydrogen cars use highly pressurised tanks, which are made out of steel to make them strong enough to be safe. However, these tanks are heavy and bulky and leave much to be desired. Another, safer method that has been suggested is solid state storage – in which hydrogen atoms are absorbed and retained within a lattice of other atoms such as titanium and aluminium. Hydrogen can be released by applying heat. However, this technology is still in the early stages of development.