Fuel cells  are hot news  at the moment, with advances being made every day. And now a US team has built the world's smallest fully-functioning hydrogen  fuel cell that measures just 3mm on a side.
While conventional battery tech  is also advancing, the reusability and potential eco-benefits of fuel cells will see them embedded in future gadgets of all sizes up to electrically-powered vehicles. But at the smallest scale it's very hard to compact all the control electronics, pumps and chemistry down to such tiny sizes without creating a fuel cell that needs more power to run than it can generate.
University of Illinois researchers got around this problem in truly classic style--by simplifying. Their tiny cell has just four components and is designed to pump its own fuel into the reaction chamber.
Inside there's a membrane separating a water chamber from another chamber containing metal hydride, behind which are the device's electrodes. Surface tension pulls water through the membrane pores into a water vapor cloud. This reacts with the hydride to form hydrogen gas, which then pushes up on the membrane to stop water flow, and reacts with the electrodes to generate electricity.
It's a closed system--unlike other cells which house the fuel separately, its tank is internal. And because it doesn't rely on gravity to move fuel through it, the team thinks it's ideal for pocket-sized gadgets.
For now the device is experimental, and generates a fairly low energy output of 0.7 volts at 0.1 milliamps for the 30 hour lifespan of the fuel. But as the technology is refined, these figures will surely rise. The pocket-sized fuel cell really is just around the corner.
[New Scientist ]