Fuel cells power up for notebooks
By Yoshiko Hara, EE Times
September 22, 2003 (11:58 a.m. EST)
URL: eetimes.com
Tokyo - NEC Corp. and Toshiba Corp. last week showed prototypes of fuel cells that they said would find their way into notebook computers before the end of next year. The direct-methanol fuel cells weigh in at about 900 grams each and can power a system for five hours, with one fill-up of methanol fuel.
NEC plans to market a notebook PC with a built-in fuel cell by the end of 2004. It also intends to launch a notebook equipped with an internal fuel cell that offers 40 hours of continuous operation by the end of 2005. Toshiba, too, aims at introducing its first fuel cell product for PCs in 2004.
NEC's fuel cell achieved an output density of 50 milliwatts/cm2, which the company termed the highest density ever reported. It consists of a polymer electrolyte sandwiched by carbon electrodes with catalyst particles.
Since the reaction occurs at the surface of the catalyst, engineers strive for materials with fine particles in order to enlarge the surface space. NEC researchers used single-walled carbon nanohorn aggregates, a type of carbon nanotube, to adsorb the platinum catalyst particles. That results in platinum catalyst particles supported on carbon nanohorns at about 2 nanometers, which the company said is much finer than possible with conventional carbon-black materials.
The prototype cell has an average output of 14 W (maximum, 24 W) at 12 V. The cell weighs 900 grams, including 300 grams of fuel; the weight with a PC attached is 2 kg. The fuel has a concentration of about 10 percent methanol.
Development of the prototype was aided by a nanocarbon R&D project jointly organized by the Ministry of Economy, Trade and Industry and the New Energy and Industrial Technology Development Organization.
Toshiba's prototype-shown, like NEC's, at the WPC Expo 2003 trade show in Chiba, Japan-measures 275 x 75 x 40 mm, or about half the size of the notebook to which it is attached. The prototype generates 12 W average and 20 W maximum. It can power the notebook PC for about five hours on a single, 50-cc cartridge of methanol fuel.
Methanol in a fuel cell generates power most efficiently when its concentration in water is 3 percent to 6 percent, Toshiba said. But thin methanol liquid has little energy, so a bulky fuel tank has been necessary for long electricity generation-clearly a hurdle for portable applications.
Dilution solution
Toshiba engineers solved the problem by making use of water, a by-product generated by the cell itself. A dilution device makes it possible to store highly concentrated methanol and reduce the tank size and weight to 33 x 65 x35 mm and 72 grams in the case of a 50-cc methanol cartridge. That's about 1/10 the size of the tank that stores the same volume of methanol in a 3 to 6 percent concentration, the company said.
Toshiba has also prepared a 100-cc cartridge, which it says can power a PC for about 10 hours. It measures 50 x 65 x 35 mm and weighs 120 grams. Toshiba engineers are working on bringing down the size of the fuel cells and cartridges, and on determining the best fuel density from the viewpoint of safety. |
