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Miniature fuel cells

Batteries not included?

May 15th 2003 | NEW ORLEANS
From The Economist print edition








Will tiny versions of the fuel cells now being developed for cars soon power laptop computers too?

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AS VIDEO telephony, broadband internet links and other high-powered features are added to laptop computers, personal digital assistants (PDAs) and mobile phones over the next few years, the energy demands of these devices will soar. The Samsung Advanced Institute of Technology, the research arm of the chaebol of that name, estimates that such upgraded portable devices will require power sources with at least 500 watt-hours per kilogram of energy stored in them. Lithium-ion batteries, today's best, can manage half that, but even the most optimistic estimates suggest that only a 30% improvement could be squeezed out of such batteries.

But there may be an alternative. Miniature fuel cells, which generate electricity by reacting hydrogen with oxygen, can do much better than batteries—at least in a laboratory. The question is whether they can ever do so in the real world. This was the subject of a conference organised last week in New Orleans by the Knowledge Foundation.



It's not a gas


The first hydrogen economy
May 15th 2003
Batteries not included
Jun 21st 2001


Computer technology


Medis Technologies outlines its agreement with General Dynamics to design and develop a recharger for a “ruggedised” military PDA. See also MTI MicroFuel Cells and the Knowledge Foundation.





The key to making fuel cells small is to replace the hydrogen—or, rather, to deliver it in a non-gaseous form, since it is hardly practical to fit portable electronic devices with pressurised cylinders. In the long run, there may be ways round this, for instance by absorbing the gas in metal hydrides or carbon nanotubes. But in the short term the solution seems to be to deliver the hydrogen as part of a hydrogen-rich compound, such as methanol. This is a liquid, which means it is easy to handle. Sachets of methanol fuel, purchased at newspaper kiosks, rather like refills for cigarette lighters, could be inserted with little fuss into electronic devices.

There are two ways to get the hydrogen out of methanol in a way that a fuel cell can use. One, being pursued by several companies, notably Motorola, is called reformation. This attempts to replicate in miniature the complicated networks of piping, heaters, vaporisers, heat exchangers and insulation that the petrochemical industry uses to extract hydrogen in bulk from methane, a chemical one oxygen atom different from methanol. That is hard—doubly so, since reformation works best at 200°C.

There are some variations on the theme, but most of those building miniature methanol reformers use an approach not much different from the one used to make circuit boards for computers. They laser-drill holes into tiny ceramic wafers to guide the flow of fluids. Then they stack these one on top of another, like layers of a sandwich, sinter them together at a temperature of 800°C, and laminate them. Presto, a mini-chemical plant.

The alternative to reformation is to feed the methanol directly into the cell, and rely on a catalyst to break it up at the electrodes, where the hydrogen is separated into its constituent electrons (which form the current that the cell produces) and protons. The trouble with this approach is that pure methanol tends to get everywhere, and thus wrecks the cell. Diluting it with water reduces this problem, but also reduces the power output.

At least one firm, however, thinks it can get round this. MTI MicroFuel Cells, based in Albany, New York, boasts some top researchers poached from the Los Alamos National Laboratory in New Mexico. One of them, Shimson Gottesfeld, told the conference that the firm has developed a cell that can use undiluted methanol. This, he claims, allows it to achieve more than three times the energy density of lithium-ion batteries.

Dr Gottesfeld was reluctant to go into details. But the secret seems to lie in some clever internal geometry, which eliminates the need for pumps. That, in turn, reduces the tendency for methanol to go where it is not wanted. However the trick is performed, though, MTI has working prototypes. It also has a contract. Its cells are due to go to market next year as part of a hybrid power-pack (that is, one which also involves batteries) being built by a large equipment firm called Intermec for use in handheld computers.

Better ways of handling methanol are not the only possibility, though. Another is to find further alternatives to elemental hydrogen. That is the route chosen by Medis Technologies, an Israeli-American firm. Its fuel is a mixture of glycerol and sodium borohydride. These react in the presence of a platinum and cobalt catalyst, generating protons and electrons in the same way as methanol—or, indeed, pure hydrogen.

Although many at the conference were sceptical, suggesting for example that the Medis cell works only when it is standing up, the firm remains bullish. Gennadi Finkelshtain, Medis's principal scientist, acknowledges his device's sensitivity to its orientation, but insists that he has a solution in the works. The fact that he has persuaded General Dynamics, a big defence contractor, to form a partnership with him to supply the American armed forces with the new device suggests that the problems cannot be too great. Medis showed off a prototype recharger for a “ruggedised” military PDA that it says it will start manufacturing next year.

None of this adds up to a revolution in portable power, of course, but it is a tantalising start. As so often with new technologies, military applications are important drivers. The American army is keen to have more energetic and longer-lived power sources for such things as climate-controlled bodysuits, advanced mobile-communications equipment and more sophisticated sensors. But consumers will soon be able to purchase lightweight fuel cells, too. Even though they are unlikely ever to be compact enough for use in mobile phones, they could act as portable chargers for such phones. And in devices that are only a bit larger, they could, indeed, end up replacing batteries.