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Friday, 16 June, 2000, 11:30 GMT 12:30 UK
Fuel cells get even cooler
Fuel Cell BBC
Scientists in Japan have taken fuel cell technology another step forward.

They have built a prototype power unit that can run on natural gas and operate at temperatures much lower than has been achieved by many other designs.

Fuel cells could become the preferred means of power generation in the future, driving our cars and lighting our cities.

The technology is simple in concept: electricity is produced when a fuel reacts with oxygen in the presence of a catalyst. It is the reverse of the familiar process of electrolysis in which electricity is used to split a compound into its component parts - such as the extraction of metal aluminium from its ore.

Fuel cells have low emissions, producing none of the toxic substances pumped out by conventional combustion engines.

New materials

They are built like batteries with two electrodes (the anode and cathode) and a conducting electrolyte in between. Researchers would like to use hydrogen as a fuel but this would be expensive to refine and distribute.

So, many designs are now using fuels like methane, ethane and propane to generate the electricity in the reaction chamber.

This has led to the development of solid oxide fuel cells (SOFC) which include components made from novel materials. Unfortunately, researchers have found that these ceramics need to work at high temperatures to drive the reaction forward efficiently and allow oxygen ions to conduct through the electrolyte.

Temperatures are typically in the region of 600 to 1,000 degrees Celsius. Now, Takashi Hibino and colleagues, from the National Industrial Research Institute of Nagoya, have brought the operating temperature down to less than 500 deg C.

They pumped the fuel and air into a single chamber containing the electrodes and an electrolyte wafer made from cerium oxide doped with samarium.

Nickel on one side of the wafer acted as the anode. The cathode was a ceramic composite of samarium, strontium, cobalt and oxygen.

Hot deposits

As in other SOFCs, oxygen from the fuel-air mixture grabbed electrons from the external circuit at the cathode and migrated through the electrolyte to the anode where it reacted with carbon monoxide and hydrogen - the two molecules produced when the hydrocarbon fuel is broken down at the anode.

The fuel cell gave out carbon dioxide and water, and, crucially, electricity.

The Nagoya set-up tested ethane, propane and methane as a fuel, although liquid petroleum gas or butane would work just as well, the researchers said.

The team also found that the lower operating temperature deterred the build-up of carbon deposits that can sometimes accumulate at the anode of a fuel cell.

The research is published in Science.

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