The quest to make hydrogen the fuel of the future
Box 1 | Storing and distributing hydrogen
If you take the trip between the communities of Whistler and Victoria in Canada, you'll see what it could be like if we converted to a hydrogen economy.
Over the 192 kilometre stretch of road, you'll find the 'hydrogen highway' project being set up by the government of British Columbia. The road will have a series of hydrogen refuelling stations, as well as demonstration projects highlighting hydrogen and fuel cell technologies.
The aim of the project is to have the highway up and running for hydrogen vehicles by 2010, when the eyes of the world will be on Vancouver as it hosts the Winter Olympics. Once completed, you'll be able to fill up your hydrogen vehicle when you want and drive on, almost as easily as if you had a petrol vehicle.
Hydrogen highways and demonstration projects like the hydrogen bus trials (Ecobus) in Western Australia are important prototypes to help address the storage and distribution issues associated with hydrogen. Without the right infrastructure, hydrogen won't catch on as a replacement fuel, simply because people won't be able to access it easily.
Currently, hydrogen is mostly made for industrial purposes such as fertilisers, plastics and petroleum products. It can be transported to end users via pipelines – which is the cheapest method – but there are relatively few existing pipelines compared with natural gas systems. Installing new pipelines can be costly at between $300 000 and $600 000 per kilometre.
Compressed hydrogen gas can be transported via roads, but the required trailers with high-pressure storage tubes are expensive, especially for long distances.
Liquid hydrogen, or cryogenic hydrogen, can be produced by cooling the gas to –253ºC. Liquid hydrogen takes up 1/700th of its normal gaseous volume and can be trucked long distances. But this is also expensive, as you need strong, well-insulated tanks; in addition, cooling hydrogen to a liquid uses a lot of energy.
However, getting hydrogen to fuelling stations isn't the only storage issue. You also have to find a way of storing it in your vehicle. Even compressed to a liquid, hydrogen provides only a quarter of the energy of the same volume of petrol. That means you would need a tank four times the size of a petrol vehicle tank to drive a fuel cell vehicle the same distance. Although it is used in larger vehicles, the large tanks required to carry hydrogen are currently a major obstacle to its widespread use in cars.
But there are more ingenious ways of storing hydrogen involving advanced (solid state) materials. By associating hydrogen with these solid materials inside a tank, more hydrogen can be stored than in liquid hydrogen tanks.
Some of these materials – such as metal hydrides and complex chemical hydrides – can store hydrogen atoms by absorbing them into their framework, where they bond with the host material. Metal hydrides store reasonable amounts of hydrogen but many need high temperatures to release the hydrogen when needed and refuelling can be slow. Complex chemical hydrides store more hydrogen but can be costly and need to be regenerated with hydrogen in a processing plant. Although advanced materials are very promising in terms of the amount of hydrogen that can be stored, the challenge remains to ensure that the hydrogen can be quickly released on demand to cope with, say, the extra energy needed at a moment's notice to accelerate a vehicle.
Other more futuristic materials – such as carbon nanotubes – store hydrogen by having hydrogen simply 'stick' to their surface in a process called adsorption. These materials work by increasing the surface area available for the hydrogen to 'stick' to. Hydrogen can also be stored by this method in metal-organic frameworks (being investigated at the University of Sydney) but they have the drawback of needing very low temperatures and high pressures to be effective.
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Box 2. Hydrogen – too hot to handle?
Related sites
Hydrogen energy: Challenges and prospects (The Royal Society of Chemistry, UK)
Hydrogen highway (Canada)
Fill her up with caged hydrogen (New Scientist, 24 May 2003)
Hydrogen storage (US Department of Energy )
Hydrogen distribution and delivery infrastructure (US Department of Energy )
Solid (state) progress (Scientific American, 13 June 2005)
Hydrogen storage in nanoporous materials (Australian Academy of Science )
Hydrogen storage: Status and prospects (Australian Academy of Science )
External sites are not endorsed by the Australian Academy of Science.
Posted September 2008.