Use of hydrogen as fuelhttp://www.uic.com.au/nip73.htmBurning...

Use of hydrogen as fuel
http://www.uic.com.au/nip73.htm

Burning hydrogen produces only water vapour, with no carbon dioxide or carbon monoxide.

Hydrogen can be burned in a normal internal combustion engine, and some test cars are thus equipped. Trials in aircraft have also been carried out.

However, its main use is likely to be in fuel cells. A fuel cell is conceptually a refuelable battery, making electricity as a direct product of a chemical reaction. But where the normal battery has all the active ingredients built in at the factory, fuel cells are supplied with fuel from an external source. They catalyse the oxidation of hydrogen directly to electricity at relatively low temperatures and the claimed theoretical efficiency of converting chemical to electrical energy is about 60% (or more). However, in practice about half that has been achieved, except for the higher-temperature solid oxide fuel cells - 46%.

The hydrogen may be stored at very low temperature (cryogenically), at high pressure, or chemically as hydrides. The last is seen to have most potential.

One promising hydride storage system utilises sodium borohydride as the energy carrier, with high energy density. The NaBH4 is catalysed to yield its hydrogen, leaving a borate (NaBO2) to be reprocessed.

. The first fuel cell electric cars running on hydrogen are expected to be on the fleet market during this decade and the domestic market by 2010. Japan has a goal of 5 million fuel cell vehicles on the road by 2020. (Current electric car technology relies on heavy storage batteries, and the vehicles have limited endurance before slow recharge.)

Current fuel cell design consists of bipolar plates in a frame, and developer of the proton exchange membrane type, Dr Ballard, suggests that a new geometry is required to bring the cost down and make the technology more widely available to a mass market.(Re fuel cells: see Fuel Cells 2000.) Other reviews point out that fuel cells are intrinsically not simple and there are no obvious reasons to expect them to become cheap.

Hydrogen can also be used for stand-alone small-scale stationary generating plants using fuel cells - where higher temperature operation (eg of solid oxide fuel cells) and hydrogen storage may be less of a problem or where it is reticulated like natural gas.