Nippon Telegraph and Telephone has developed a prototype fuel cell that it hopes to commercialise within three years at a size small enough to fit inside mobile phones and other portable consumer electronics devices.

The prototype works by combining hydrogen with oxygen, generating electricity and water. It is more powerful than the DMFCs (direct methanol fuel cells) currently being developed by many companies, said a spokesperson.

The power density of the NTT cell, which is a measure of the amount of power it can generate relative to its size, is up to 200mWpcm2 (milliwatts per square centimetre). When the fuel cell is commercialised, it will be able provide a third-generation mobile phone that uses 2.5W of power with about nine hours of talk time, the spokesperson said.

In contrast, a DMFC developed by NEC last year offered a power density of 70mWpm2. NTT calculates that to match the size of lithium ion batteries used in mobile phones, a fuel cell must have a power density of about 160mWpcm2 or more, he said.

"DMFCs can't do it. There isn't enough power," Akiyama said.

NTT believes that the extra power advantage means hydrogen-fuelled PEFCs will be able to replace lithium ion batteries inside mobile phones and in tests the prototype has been able to power a phone long enough to allow a video or voice call, he said.

NTT's prototype currently measures 1.5x1.7x3.1in and weighs 94g. It will take two years before the company can shrink this so that it can fit inside a cell phone, Akiyama said.

The hydrogen-fueled PEFC technology does have at least one disadvantage compared to DMFC technology, he said.

Methanol fuel cells can work off small, nonpressurised cartridges of the liquid while hydrogen-fuelled PEFCs require pressurised hydrogen gas. While the hydrogen is only pressurized to two or three atmospheres, the industry has yet to create a small, safe and standardised container for this.

NTT has designed a hydrogen storage unit that is slightly bigger than an automobile battery that can store 50l of hydrogen. In the home, it could be used as a refuelling station for a number of types of fuel cells, although is too big for portable use.

Building a supply and container infrastructure, creating international packaging standards and making a legal framework to allow transportation of hydrogen canisters will take about 3 years, a year longer than it will take to resolve similar issues with methanol, Akiyama estimated. Regulations to allow passengers to carry methanol fuel canisters onboard commercial airliners should be completed around 2007.

"The fuel canisters we are using are very heavy and we need to make them smaller and lighter, and safety is a big concern," he said.