World's smallest working fuel cell

Chemical engineers from the University of Illinois at Urbana-Champaign say they've developed a working fuel cell measuring 3 millimeters across. Future versions of the tiny hydrogen-fuelled power pack could replace batteries in portable gadgets.

While batteries are used to do that today, fuel cells are able to store more energy in the same space. Even the most advanced batteries have an energy density an order of magnitude smaller than that of a hydrogen fuel tank.

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This fuel cell system is designed for portable devices that move and rotate. Instead of gravity controlling the flow of water, the fuel cell uses surface tension, which is unaffected by the device moving.

Inside the fuel cell, a thin porous membrane separates a water reservoir from another containing metal hydride, below which is an arrangement of electrodes. Water molecules pass through the membrane as vapour and then react with the metal hydride to form hydrogen.

Batteries are much easier to make at the small scale than the pumps and control electronics of a fuel cell. And small pumps can use more energy than they generate.

Other pump-less fuel cells use gravity to push water through the system, but this cell's so small, it can use surface tension instead. That allows it to work even if its position is altered.

You may have to wait a while for the first commercially available model, because so far it’s only able to generate 1mA of electricity.