Hydrogen could become the world's car fuel of choice, but how could the most common element of all also become the most common fuel in your tank? Science Editor Dick Ahlstrom reports
In the old days smart young graduates were encouraged to get into plastics. Today it is hydrogen, the fuel of the future.
All of the world's leading motor manufacturers are studying hydrogen-powered cars and have prototypes whizzing around test tracks. They don't burn the hydrogen however, they use it in a chemical reaction to produce electricity.
The technology behind the new hydrogen cars is based on a device known as a fuel cell. These take oxygen and combine it with any of a variety of hydrogen sources to produce electricity, heat and water.
Of course, if you choose a fuel cell car you are actually choosing an electric car. The fuel cells are used to produce electricity and then this is used to drive electric motors, with many designs and prototypes providing four-wheel drive power with an individual motor on each wheel.
Fuel cells represent the Promised Land for motor manufacturers with an environmental conscience. If hydrogen gas is used, then the only thing coming down the exhaust pipe is pure, drinkable water.
Fuel cells have a long and distinguished history. They provided electricity and of course fresh water on board the Apollo and Gemini manned spacecraft and the space shuttle. They were chosen for electricity generation in preference to radioactive sources, which were considered too dangerous.
More recently fuel cells are powering road vehicles. Late last year Honda and Toyota became the first to lease environmentally-friendly fuel cell cars, making four available to the Japanese government.
The great drawback to the fuel cell approach, however, is cost. The Japanese lease arrangements are about 40 times higher than a conventional vehicle lease.
Then there is the inherent risk of carrying around pressurised gases as a fuel source. Hydrogen burns both powerfully and quickly if exposed to a live flame or ember. The ill-fated Hindenburg Zeppelin which crashed and burned in the late 1930s was filled with hydrogen gas. Even so, the environmental advantages of a hydrogen car are encouraging motor manufacturers to find engineering answers to these problems.
Some of these difficulties can be overcome quite easily, depending on the hydrogen source you choose. Pure hydrogen gas is but one source.
Hydrogen is also a constituent of the whiskey some like to sip, and the raw alcohol used to sterilise surfaces. It is found in natural gas, petrol, coal and dozens of the exotic chemicals formulated to operate in the many different types of fuel cells currently under study.
Any of these hydrogen sources could be used, but there is an immediate trade-off depending on your choice. The further you get from pure hydrogen the greater the emission problem, coming as carbon dioxide or other more complex compounds.
This variety of sources is causing something of a transatlantic schism when it comes to choosing your hydrogen. Hydrogen doesn't occur naturally as a gas, it has to be taken from something else, for example by splitting a water molecule or breaking it off a hydrocarbon such as methane. One way or the other it takes energy to free the hydrogen, and here is where the great divide occurs. The EU, which recently announced a €2.1 billion hydrogen energy research programme, favours the use of renewable energy to derive hydrogen.
The US, which has its own €1 billion hydrogen plan, is pushing the idea of taking hydrogen from fossil fuels.
One very clean method of getting hydrogen is using an electric current to split water molecules. If done using electricity from fossil fuels or nuclear power, it would cost $15 to $18 per gigajoule of hydrogen energy. If done using solar cell electricity, a completely renewable source, it would cost $25 to $50 per gigajoule.
The US alternative is much cheaper, but less environmentally friendly. Hydrogen taken directly from coal, gas or oil would cost between $1 and $5 per gigajoule. If you used natural gas and then spent extra money to sequester the carbon dioxide emissions, it would still only cost $8 to $10 per gigajoule.