Storage

Hydrogen has the potential to provide energy without burdening the environment (if produced from renewable sources such as electrolysis of water). Hydrogen is also the favourite to replace liquid fossil fuels for powering vehicles. However the key issues will be transporting and storing it safely and in a form that can provide equivalent amounts of energy to current fuels.

It is estimated that an average car would require 1.2 kg of hydrogen to travel 100 km (which is equal to about 13 500 litres of hydrogen gas). Storing hydrogen as a liquid in pressurised containers is also not practical, because of the low energy quantity per litre and the need for improved barrier systems to line the tanks and prevent hydrogen gas leakage. However transporting hydrogen as a liquid has merit for refuelling stations (this would use the same infrastructure as exists for petrol, diesel and liquid petroleum gas).

For onboard vehicle storage the only practical format is to supply hydrogen as a solid compound, such as a metal hydride. Many nanomaterials are now being tested and developed to fulfil this role including carbon nanotubes and metal organic frameworks (MOFs - pictured), which have the largest surface area of any manufactured material (1 gramme has a surface area equivalent of a football pitch). The importance of this is that a higher surface area allows a larger amount of hydrogen to be stored. The issues that still need to be addressed are improving the amount of hydrogen that can be bound and released by the compound, and ensuring this is achieved quickly (into the storage compound at refuelling stations, and from it when needed by the fuel cell).