Direct methanol fuel cell

The direct methanol fuel cell ( direct methanol fuel cell Sheet, DMFC) is a low -temperature fuel cell operating at a temperature of about 90-120 ° C works. As an electrolyte, this type of cell uses a polymer membrane ( PEM). An alternative approach used in place of the two-dimensional polymer membrane as a reaction surface a 3D architecture of porous silicon as the electrolyte by means of which at the same time saving space a larger reaction surface is achieved. This technology with operating temperatures of 25 - 50 ° C is also close to market maturity, and is initially intended for use as a military field battery and subsequently in the field of consumer electronics, such as laptops.

Principle

The fuel used in the DMFC, methanol ( CH3OH ), which is fed directly without prior reforming together with water, the anode and oxidized there. At the anode exhaust gas is produced as CO2. The cathode may be supplied as the oxidant air oxygen. The oxygen reacts there with H ions and electrons to form water.

A problem in the DMFC, methanol that migrates through the membrane from the anode to the cathode. On the one hand there occurs a loss of fuel on the other hand, as well as the electric potential is minimized and the cell efficiency decreases. The reduction of this technical problem is the subject of current research. A newly developed composite membrane of the Fraunhofer Institute can, with the use of ethanol as fuel, reduce the cross-over ( migration of the fuel through the polymer membrane) by a factor of hundred (May 2009 ).

Reaction equations

The inner charge transfer is effected by means of H ions. On the anode side, the reaction requires water and which produces at the cathode side. To meet the demand for water on the anode side is an elaborate water management required. This is realized eg by back diffusion through the membrane and humidification of the reactants.