Toshiba announced on Friday that it has built what it claims is the smallest-ever direct methanol fuel cell.

The device, which is only a prototype at present, is designed to be used in small electronic devices such as MP3 players and wireless headsets.

Including the fuel tank, the direct methanol fuel cell (DMFC) is about the size of a thumb (22mm by 56mm by 9.1mm) and, when full, will weigh 8.5 grams. According to Toshiba, the DMFC will be able to deliver 100 milliwatts of power for up to 20 hours from a single 2-cubic-centimetre shot of methanol. The Japanese company says that topping up the device with additional methanol will be an easy process.

The fuel cell industry is well-used to seeing demonstrations and prototypes of innovative devices. Commercial products are much less common, but Toshiba said that it expects DMFC-powered handheld devices to go on the market by 2005.

DMFCs generate electricity through a reaction between diluted methanol and oxygen (in the form of air), each held in opposite sides of the cell. When they come into contact at a permeable membrane, hydrogen ions flow from the methanol side to the oxygen, which also drives electrons along a circuit connecting the two sides of the cell. The methanol and oxygen are converted to carbon dioxide and water.

Earlier Toshiba methanol fuel cells used a pump to bring the methanol and water together, but the latest prototype uses a technique called a ‘passive fuel supply system’. This feeds pure methanol directly into the cell and combines it with water, setting up a concentration gradient where the fuel touching the membrane is 10 per cent methanol and 90 per cent water, as required.

Last fall, Toshiba showed off a prototype DMFC device that used an active fuel supply. This was capable of generating one watt of power but was significantly larger than this latest prototype, measuring 100mm by 60mm by 30mm.

Several other companies are also trying to crack the fuel-cell market. Earlier this week, MTI MicroFuel Cells showed off prototypes for fuel cells that could power notebooks and handheld computers, and back in January, PolyFuel demonstrated a catalytic membrane for use in methanol fuel cells for laptops and mobile phones. Toshiba’s fuel cell is functionally similar to MTI’s but MTI has argued that Toshiba’s is not nearly as efficient.