The prototype cell, to be shown at Wireless Japan 2006 in Tokyo July 19-21, is a polymer electrolyte fuel cell in the form of a battery charger measuring 24 by 24 by 70 mm with a fuel cartridge. It produces 2 watts.

Based on thin-film power unit technology from Aquafairy (Osaka, Japan), the polymer electrolyte fuel cell (PEFC) contains 10 cc of water and a hydrogen-producing catalyst. It is connected using a power unit that includes an anode, solid electrolyte and a cathode.

In the fuel cartridge, water is injected onto the catalyst to generate pure hydrogen which is then channeled to the anode in the power unit. There, the hydrogen separates into H+ ions and electrons. The electrons flow from the anode to the cathode through an external circuit, producing electricity. The hydrogen ions move through the solid electrolyte to the cathode and combine with oxygen to produce water.

Docomo has long been seeking a power supply solution using fuel cell technology. Last year, it demonstrated a prototype battery charger using a direct methanol fuel cell (DFMC), developed jointly with Fujitsu Laboratories Ltd.

The PEFC is considered to have better power- generating capability than other technologies, including direct methanol fuel cells, because it handles hydrogen directly. The PEFC prototype is less than one quarter the size and produces twice the power of the DMFC charger prototype, according to Docomo.

The prototype can produce up to 800 mAh at 3.6 V—three times that of a lithium battery commonly used for Docomo's 3G phones. One charge takes about two hours, about the same time required for charging by an AC adaptor.

Docomo aims to incorporate PEFC technology into battery chargers sometime next year. Both companies also hope to refine the technology for a power unit that can be built into mobile phones.