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Hydrogen generator could power electronic gadgets
01 October 2005
From New Scientist Print Edition.
Helen Knight

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A device designed to generate hydrogen for micro fuel cells could help meet the growing power demands of electronic gadgets.

Hydrogen has long been considered a feasible clean fuel for medium-scale fuel cell applications such as powering vehicles. But when it comes to fuel cells for hand-held devices, the difficulty of storing hydrogen or generating it from scratch on such a small scale has forced developers to focus on less energy-dense fuels, such as methanol.

Now UK defence and security specialist Qinetiq has developed a method of generating hydrogen from pellets of the chemical ammonia borane (NH3BH3). The company has signed a deal with Japanese electronics firm Olympus to develop a working prototype for fuel cells for consumer devices by 2008.

The combined generator/fuel cell will have a target peak power output of 10 watts, and should last between three and five times as long as conventional batteries, says Vishal Nayar, a business manager at Qinetiq. "Ammonia borane is almost 20 per cent hydrogen by weight, and so in terms of the overall weight to power density it could be a significant improvement."

The material is solid at room temperature but releases hydrogen when heated. The generator uses pellets of ammonia borane combined with a secret mix of chemicals that react and rapidly heat up when kick-started by gentle warming.

The pellets sit in individual compartments inside a cartridge, and can be used one by one. A microheater powered by a short electrical pulse provides the warmth to trigger the heating reaction, which in turn heats the ammonia borane. Once it reaches 100 °C, it releases hydrogen into the fuel cell until all the hydrogen is exhausted, at around 400 °C. The reaction chamber will be insulated to prevent the heat setting off neighbouring pellets or causing the gadget itself to heat up. The company has built a prototype the size of a coffee cup, and plans to miniaturise this.

Most micro fuel cells being developed for portable devices use diluted methanol. Neat methanol is not practical, as existing fuel cell membranes allow the resulting toxic vapour to escape into the air - around a mobile phone user's mouth, for example. But using diluted methanol reduces the power output of the fuel cell.

At the electronics show CEATEC in Tokyo next week, Toshiba will unveil two digital music players powered by prototype 100 and 300-milliwatt methanol fuel cells. While 100 mW may be fine for MP3 players, which require a fairly steady voltage supply, devices such as cellphones consume very little power while they are idle but can draw several watts while making or receiving a call. "You have to deliver a high voltage and high energy density to the device in a short period of time," says Nayar.

He claims ammonia borane should pose fewer safety risks than methanol, as it is very stable, and because it is a solid it will not leak.

From issue 2519 of New Scientist magazine, 01 October 2005, page 24

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