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Image: Stan Barouh

“It may not be the generic solution that goes to every infantryman, but some people are willing to take more risk to get more capability.” — Chris Bolton, chief engineer at the Communications-Electronics Research, Development and Engineering Center’s Power Division

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How fuel cells work

To everyday users of electronic gadgets, fuel cell cartridges look and behave just like normal batteries. Inside, though, the method of producing electricity is different. Batteries store electrons; fuel cells generate them.

Fuel cells mix a fuel — usually hydrogen — with air to produce electricity. On one side of the cell is a source of hydrogen, which is fed through a catalyst-coated membrane sandwiched between two electrodes, the anode and cathode. Hydrogen comes in from the anode, and air is fed through the cathode. The draw of the electrical load catalyzes the hydrogen, forming electrons and protons. The electrons — which cannot pass through the membrane — are shuttled away to feed the electrical load; the protons pass through the membrane, combine with the air and produce water vapor.

Fuel cells can be stacked to provide greater voltage if required. When the cartridge’s fuel is spent, the user simply replaces it. The cartridge can then be reloaded.

Most portable fuel cells are powered by methane rather than hydrogen. Methane is preferable for portable cells because it can be stored more compactly than hydrogen — as a liquid — and converted into hydrogen for the catalyst process.

Hydrogen is usually stored as a gas — which takes up more space — so its use in fuel cells is reserved for larger batteries, such as those that one day may power cars.

The advantages of fuel cells are many. They provide uniform voltage at all temperatures, whereas the output of batteries varies in extreme hot or cold weather. Fuel cells are instantly rechargeable by adding a new cartridge. With no moving parts, they’re also durable.

Most important, fuel cells have a higher energy density than batteries. According to UltraCell, its UltraCell XX25 cartridge can provide almost 700 watt-hours per kilogram when running at 22 watts-per-hour compared to 150 watt-hours per kilogram provided by Dell M60 laptop batteries. In terms of portability, to carry around 550 watt-hours of juice — about 25 hours of electricity for a small portable device — you’d need 7.7 pounds of lithium-ion batteries but only 3.5 pounds of fuel cell cartridges.

— Joab Jackson