American engineers develop world’s smallest fuel cell

"The 9 cubic millimeter fuel cell has been developed by chemical engineers at the University of Illinois at Urbana-Champaign and has four main modules – a water reservoir, a metal-hydride chamber, a thin membrane to work as a partition between the two and an assembly of electrodes.

The thin membrane has several small holes which let water molecules reach the metal-hydride chamber in the form of water vapor. As vapor enters the chamber it reacts with metal-hydride to produce hydrogen. As this hydrogen depletes, a fresh stock of vapor enters the chamber and ensures continuous hydrogen generation.

Presently the cell generates 0.7 volts and a current of 0.1 milliamps for about 30 hours..."