Hydrogen may be the perfect fuel. It delivers more energy per kilogram than coal or oil. Environmentalists love it. When it’s burned with oxygen the residue is pure water, and even when it’s burned with air the combustion temperature is low enough to minimise formation of polluting gases, Finally, it’s easy to transport by pipeline.

Hydrogen, now made from natural gas, is obtainable by the electrolysis of water, but economically only if electricity is very inexpensive, Electricity is used at the generating plant to produce hydrogen, which is liquefied and transported by pipeline. At the point of use, the hydrogen is converted back to electricity in fuel cells, which are highly efficient or into metallic hydride for use in vehicles.

The difficulty is that hydrogen is hard to store. Even at high pressure, you can’t store enough to run a car very far in a tank of reasonable size-one that will fit into the car. Liquefying the hydrogen is one solution. Large rockets burn liquid hydrogen and liquid oxygen, but great amounts of such fuel must be stored in tanks. For small amounts, the thermal insulation required to keep the hydrogen liquid takes up more space than the stored hydrogen. A new approach is based on storing hydrogen as a compound, a metallic hydride. The hydride, stable at room temperature, decompresses on heating to yield free hydrogen. This may solve the problem of a small “hydrogen tank for automobiles and aircraft.

A point of special interest: We don’t have to develop any new techniques in order to convert hydrogen into mechanical power. Any internal combustion engine will run on hydrogen instead of petroleum-based fuel.