What is hydrogen fuel cell?
Sir William Grove, a Welsh judge and gentleman scientist, built the first fuel cell in 1839. But the technology was not further investigated until the U.S. space program revived interest in the concept in the 1960s. Fuel cells were used in the Gemini and Apollo spacecraft in preference to the riskier nuclear and more expensive solar alternatives. The current version of the space shuttle still uses fuel cells to provide electricity and water.
There is a range of different types of fuel cell. It appears that there is no one optimum type. Each has its merits according to where and for which purpose it is to be used. Even in a single general application, such as transport, the choice of fuel cell may not be set, as different research groups follow diverging routes.
Nevertheless, all fuel cells technologies are variations on a common theme. A fuel cell is very much like a rechargeable battery, except that it is re-fuelled rather than restocked with electrical capacity. It uses hydrogen fuel to generate electricity, producing water and a little heat as by-products.
A fuel cell is effectively an electrolyte sandwiched between two electrodes. Hydrogen is passed into the anode (positive electrode) of the cell. Oxygen (or, in some types of fuel cell, air) is passed into the cathode (negative electrode). A catalyst elicits the split of the hydrogen into protons and electrons. The protons pass through the electrolyte, while the electrons create a current to the cathode, which is the source of electricity generated by the cell. At the cathode, the electrons, protons and oxygen are united to form water.
Hydrogen may be used as the immediate fuel or be derived from others in situ. The latter requires a fuel reformer. This allows any hydrocarbon fuels to be used, including natural gas, methanol and even petrol. Both of these types of fuel cell are efficient and environmentally friendly. Even though the fuel reformer cells produce carbon dioxide (a greenhouse gas), they are far more efficient than even the best combustion systems. This is because chemical energy conversion of the type used in fuel cells wastes less fuel and heat in the conversion process.
In order to achieve further Eco-efficiencies, the hydrogen is often derived from renewable resources, such as biomass or even municipal waste. In some cases, this type of sourcing can make a zero or negative contribution to atmospheric carbon levels (so reducing the greenhouse effect) and come at negative financial and environmental cost (for example, as a cheaper and preferable option to land filling).
The emissions from hydrogen fuel cells are negligible. Their use could dramatically reduce urban pollution, and its effects on health and quality of life. Depending on how the hydrogen is produced, it may even be carbon neutral, thereby helping to reduce our contribution to the greenhouse effect. The U.S. Department of Energy projects that if a mere 10 percent of automobiles nationwide were powered by fuel cells, regulated air pollutants would be cut by one million tons per year and 60 million tons of the greenhouse gas carbon dioxide would be eliminated.
London's fleet of 17-18,000 diesel taxis make a considerable contribution to pollution in the city. They emit 1.6 million kilograms of assorted pollutants, including CO2 and particulate matter. Atmospheric pollution in cities carries many associated costs, including those to public health, buildings and the wider issue of quality of life. In response to this challenge a company called Zevco (the Zero Emission Vehicle Company), has launched the world's first pollution-free taxi. The Zevco taxi looks indistinguishable from the latest generation black London taxi. However, the Millennium Taxi, as it has been dubbed, is powered by a hydrogen fuel cell. Electricity is generated in the cell by combining hydrogen with atmospheric oxygen in the presence of a catalyst to generate electricity. When the taxi is on the move, the electricity is used to power an electric motor. When it is stationary, the fuel cell charges a battery which is used as a supplementary source of power. This actually makes it a hybrid electric vehicle. Its only by-product is water.
Zevco is one of a number of organisations currently developing hydrogen fuel cell vehicles, including giants like - Daimler Benz, Ford and Toyota. It is however, one of the first to release a vehicle onto the market. It has also taken a different technology route to most of its competitors. While many are investing in a form of fuel cell known as a proton-exchange membrane, which uses relatively cheap materials, Zevco uses an adaptation of alkaline fuel cell (AFC) technology.
AFC's were first used in spacecraft and, whilst having a superior power to weight ratio, they have two barriers to their wider use: they need pure oxygen to function; and they use expensive platinum to plate the electrodes. Zevco is using a carbon dioxide scrubber to solve the first problem. The second problem is being addressed by learning to keep platinum use to a minimum. It is hoped that cobalt may be used as a cheaper substitute in the future, which should reduce costs considerably.
The Millennium Taxi costs £2,500 more than a standard cab, but its running costs are lower. Zevco claims that it could save operators £30,000 in ten years, which is more than the original purchase price of the taxi.
© 2000 Mena Report (www.menareport.com)