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Archive
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The
internal combustion engine as used in our cars was
first conceived more than one hundred years ago. It was dreadfully inefficient then and it's even more so now. Indeed, if some late developer type scientist came up with the idea today, he (or she) would probably be laughed out of court. |
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To some people, talk of fuel cells may be taking things into the realms of science fiction and Space War technology, but the basic concept pre-dates the internal combustion engine, when a Welsh judge and part time scientist, Sir William Grove, built one in 1839. Given the conditions and materials of the time, it wasn't an economic or practical proposition and very few advances were made until the 1960's, when NASA chose fuel cells over more expensive solar energy and potentially dangerous nuclear power. Fuel cells furnished power for the Gemini and Apollo spacecraft and are still used to assist in the provision of electricity and water for the space shuttle. But exactly what is a fuel cell? Those of you who can remember your school days, no doubt also remember the chemical formula for water, H2O and, if you were really clever you will also know that this represents two atoms of hydrogen (H2) to one of oxygen (O). Furthermore those in the more advanced classes may have experimented with the process of electrolysis, where passing a current through two electrodes in (pure) water could break the water down into its constituent parts - hydrogen and oxygen. What Sir William did with his fuel cell was to reverse this process and combined hydrogen and oxygen gases to produce electricity and water.Modern versions do exactly the same, although perhaps a little better. In principle, a fuel cell operates something like a single cell battery and, like a battery, coupling a number of cells together can increase its power and output. However, unlike a battery, a fuel cell does not require recharging. It will continue to produce energy in the form of electricity and heat as long as fuel is supplied.
As with batteries, there are various types of fuel cell, but the one that we will probably see in all automotive applications dispenses with the electrolyte as such and use a sort of 'dry-plate' construct-ion where the two electrodes are separated by a thin wafer-like material called the Proton Exchange Membrane or PEM for short. This membrane is coated on both sides with micro thin layer of metal particles (mostly platinum) acting as catalysts. Hydrogen fuel is fed into the anode of the fuel cell. Oxygen (or air) enters the fuel cell through the cathode. Encouraged by a catalyst, the hydrogen atom splits into a proton and an electron, which take different paths to the cathode. These electrons create a separate current that can be utilised before they return to the cathode where they are reunited with hydrogen and oxygen in a molecule of water. All fuel cells, including the PEM versions, need hydrogen and oxygen and, while a ready supply of oxygen is no trouble since there's plenty in the air we breathe, hydrogen does create a storage problem in automotive applications. On vehicles, hydrogen can be stored as a cryogenic (low temperature) liquid or as a pressurised gas. But liquefying hydrogen to -253C is expensive and highly energy-intensive as are the energy absorbing pressurising pumps for gaseous versions. In both cases as well it would involve the use of bulky (crash-proof) storage tanks and even more stringent safety controls at filling stations than with petrol.
A fuel cell system which includes a 'fuel reformer' can utilise the hydrogen from any hydrocarbon fuel - from natural gas to methanol, and even gasoline. But, in addition to the greater space needed this involves more machinery, more complication and additional weight, none of which is ideal in a road going vehicle. In fact methanol is, in many ways, the ideal fuel. It has a high hydrogen content (chemical formula CH3OH), it has no sulphur (which is fuel cell contaminant) and, most important, it is liquid at normal room and ambient temperatures. However, it still needs a reformer to convert it into hydrogen. Or rather it did, for the latest development is a Direct Methanol Fuel Cell (DMFC). These are similar to the PEM cells in that they both use a polymer membrane as the electrolyte. However, in the DMFC version, the anode catalyst itself draws the hydrogen from the liquid methanol, eliminating the need for a fuel reformer. Admittedly, methanol is normally derived from hydrocarbon fuels such as coal, gas, oil, but reserves are far greater (or less expensive to extract) than with petrol or diesel and emission levels during the production process can be restricted without too much trouble. In use, of course, the fuel cell relies on chemistry and not combustion, so emissions from this type of a system would still be much smaller than emissions from the cleanest (catalyst equipped) motor cars.
Despite its 1839 birthday, the fuel cell is still in its infancy and especially so for automotive purposes and there is still a long way to go before it's acceptable to the motoring public both on cost and performance terms, but its day will come. As far as the general public is concerned, we shall probably see fuel cell powered mobile phones and lap-top computers long before there's one up front in our cars but fuel cells in one form or another are still the number one contender to replace that reciprocating/rotating lump we have at present. Finally,
perhaps the nearest we shall ever get to perpetual
energy is the Regenerative fuel cell. Still at
a very early stage of development, the regenerative
fuel cell combines with solar power to create
a sort of closed-loop form of power generation.
Water is separated into hydrogen and oxygen by
a solar-powered electrolyser. The hydrogen and
oxygen are fed into the fuel cell which generates
electricity, heat and water. The water is then
recirculated back to the solar-powered electrolyser
and the process begins again. It's like a solar
powered battery that keeps going, even when the
light goes out.
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