Hydrogen fuel cells may be decades away from widespread use in cars, but later this year, consumers will be able to buy a fuel-cell generator that's light and compact enough to grab off a shelf during a blackout--or even take on a backpacking trip. The 22-­centimeter-tall generator weighs about two kilograms with an unactivated fuel cartridge. Add water, plug in a device, and the system pumps sodium borohydride solution over a catalyst, freeing hydrogen to power the cell.

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