Docomo and Fujitsu are jointly developing fuel cells for Docomo's mobile phones. The partners demonstrated their first prototype last September using a 30-percent methanol fuel concentration.

Higher concentrations of methanol mean more power can be generated from the same volume solution. But passive fuel cells lack an active mechanism to drive the flow of liquid, a phenomenon know as "methanol crossover." Fuel permeation between battery electrodes occurs when highly concentrated methanol is used directly in a passive fuel cell, but the process reduces power efficiency.

Fujitsu Labs overcame the phenomenon by developing a solid, electrolyte film that reduced the methanol crossover effect by half compared to earlier films. The technique controls the flow of water generated at the cathode. Water is a by-product of power generation to the anode, diluting the methanol fuel. Using the new film and a by-product wafer, Fujitsu Labs said it has preserved power generation efficiency using a high concentration of methanol fuel.

Consequently, the same volume of methanol can generate three times the power of an earlier prototype using 30- percent methanol. The new prototype was demonstrated in an external recharger for Docomo's 3G FOMA handset. The fuel cell charged a lithium-ion handset battery with a 700-mA capacity at 5.4 volts three times using 18 cc of methanol.

Docomo hopes to complete fuel cell development for use in an external recharger by March 2006 and finish a built-in fuel cell within two to three years, a Docomo spokeswoman said. "The performance of power generation has almost achieved our target. The next step is to minimize the system size so that we can build it into the fuel cell in a mobile phone," a Fujitsu spokesman said.

The partners will show the prototype at exhibitions here next week (July 13-15).