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FUEL CELL OUTLOOK

Although large commercial fuel-cell power generation plants providing power in the megawatts have been built, these were isolated experiments that generally proved somewhat too ambitious. Companies developing fuel cell systems for power generation have instead turned to manufacturing smaller units.

Current commercial fixed site fuel cell power systems are based on PAFC technology and provide outputs in the range of 50 to 200 kilowatts. These systems are useful for power cogeneration at fixed sites, such as hospitals, or remote locations where network power is unavailable or uncertain. While costs still remain high in comparison to diesel or other backup power systems, the relatively clean nature of fuel cells and their low maintenance make them attractive. They operate at a very constant efficiency, no matter what the output power load is.

Government assistance in the form of subsidies to manufacturers and tax breaks to purchasers has allowed the installation of practical fixed site PAFC power systems. In some cases, they have been installed at landfills, sewage treatment plants, and food processors where they can be used to burn waste methane and reduce the cost of operation. Fuel cell systems incorporating a small gas power turbine and offering power output in the megawatt range have been built on an experimental basis, but are not yet commercially available.

Small systems about the size of a large refrigerator and with output power in the range of 3 kilowatts are now being designed as household power supplies, using natural gas as fuel. Ironically, these small systems generally use a bank of lead-acid batteries to help meet peak power demands, with the batteries recharged by the fuel cell system when demand falls off. A number of manufacturers in the US, Europe, and Japan are working on such residential power systems, and speak of having them on the market in a few years.

Although PAFC systems have been used to experimentally power buses and other large vehicles, they are simply too big and cumbersome for use with a normal automobile. Major automobile manufacturers have built test prototypes of vehicles using PEM cells as powerplants.

An automotive fuel cell system must provide about 50 kilowatts of power, though a hybrid vehicle could use a 15 kilowatt fuel cell system along with a battery system to provide peak power. Such a hybrid system could also improve automobile efficiency by providing "regenerative braking", where the braking system feeds power back into the batteries. However, hybrid vehicles tend to be relatively complicated and expensive.

Prototype automobiles powered by fuel cells operate on methanol and have ranges comparable to those of conventional gasoline powered automobiles, but costs for fuel cell powered vehicles still remain uncompetitive. Despite the expense, interest remains high because of increasingly aggressive antipollution laws, particularly in California, and the oil companies are showing interest in fuel cell powered vehicles along with the automobile manufacturers.

Another advantage of fuel cells for automotive applications is that they can use a variety of different fuels, such as methanol, methane, or gasoline. The ultimate dream of "clean car" advocates is a fuel cell vehicle operating directly off hydrogen fuel and exhausting little but water. However, developing distribution and storage systems for hydrogen is a formidable engineering prospect, and it is not likely to happen in the near term.

Work on PEM fuel cells for portable electronics equipment, such as handheld computers or cellphones, remains speculative but very interesting. Prototypes of such "micro fuel cells" (MFCs) have been built, in one case using microcircuit fabrication techniques to pattern the components. Other research has focused on low-cost catalytic schemes using platinum and ruthenium to allow the anode to directly break down fuel into hydrogen, without need for a fuel processor.

MFCs potentially offer 40 or 50 times the endurance of nickel-cadmium battery packs at half the weight, though with the same volume. MFCs would be powered by a disposable methanol cartridge, allowing for an instant "recharge". How the exhaust products are handled is an interesting question, but the idea remains intriguing.

More exotic classes of fuel cells are now being investigated in the lab. One particularly interesting item is a "biofuel cell" designed to power bioimplants, with the energy derived from the body itself.

The scheme has been developed by researchers at the University of Texas at Austin and TheraSense, a California startup. The cell combines hydrogen obtained from glucose, or blood sugar, and oxygen in the bloodstream to produce electricity. The biofuel cell consists of two carbon electrode threads, each about seven microns in diameter, linked to a cell encased in plastic. Each of the threads is coated with enzymes designed to promote the proper electrode reactions. The cell can generate a maximum of 0.8 volts and 0.6 microwatts of power, adequate to run a low-power silicon chip.

Since putting anything with a medical application into production is very risky, the researchers believe that the first application of the biofuel cell should be to power tracking devices that can be implanted into insects or other small animals. Once it has been proven safe and effective in this application, it can then go on to use in humans, possibly in blood sugar monitors for diabetics.

An even more interesting scheme is to build fuel cells driven by microbes that obtain their energy by breaking down biomass. In 2003, researchers at the University of Massachusetts, Amherst, published a paper that described such a fuel cell. They used a two-chamber water tank, with each chamber containing a solid graphite electrode and the two electrodes connected by a wire. One chamber was used to support a culture of a bacterium named Rhodoferrax ferrireducens, found in marine sediments, that could generate excess electrons as part of its metabolic processes.

When fed sugars, the bacteria grew and coated the graphite anode on their side of the tank, pumping electrons through the circuit. Conversion efficiency was very high, about 80%, compared to the 50% obtained from experiments elsewhere along this line, though the reaction and power rate was still low. In any case, this was strictly a lab demonstration that was not remotely near practical application. The Amherst researchers were interested in developing the scheme as a power source for remotely deployed marine instruments, but feel that over the long run the approach might be able to produce significant amounts of power from waste biomass sources.

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