Metal-Air-Cell

From a technical point of view Metal-Air-Cells are no fuel cells but rather primary batteries. However, since the potential of Metal-Air-Cells is significant and Metal-Air-Cells and fuel cells can address similar applications, the basics of Metal-Air-Cells are described here. Other than fuel cells, Metal-Air-Cells use metalls such as zinc, aluminum and magnesium as fuel. The power stored in these metals is quite high (energy density) and therefore it is possible to achieve impressive power densities with such systems. The following Metal-Air-Cells are the most commonly used:

Function of the Metal-Air-Cell (Example Zinc-Air-Cell)

Anode reaction: Zn + 2 OH --> ZnO + H₂O + 2e
Cathode reaction: ½O₂ + H₂O + 2e --> 2 OH -
Complete reaction: 2Zn + O₂ --> 2ZnO

The Zinc-Air-Cell consists of a Zinc anode, which is surrounded by an aqueous electrolyte (KOH). For the cathode, often a layer of carbon is used, which offers good electrical conductivity and allows the air to circulate thru the cathode. The oxygen from the air moves thru the carbon cathode and gets in touch with the electrolyte. As a result the zinc of the anode gets oxidized and ZnO is generated. The free electrons released by this reaction can be used to drive an external electrical load. The cell voltage at open circuit is app. 1,4V when a zinc anode is used. The Zinc-Air-Cell produces electrical power as long as metallic zinc is available. When zinc is used for the anode, it is possible to recycle the ZnO back to zink by a electrolysis process which consumes energy. So it is possible to achieve a closed loop for the fuel zinc (more details see Electric Fuel Corp. www.electric-fuel.com)

Function of a Zinc-Air-Cell (Source: www.electric-fuel.com)

Today the metal-air-cell technology suffers in several areas. The construction of a efficient cathode, which provides enough oxygen for the electrochemical reaction and the removal of Metal oxide from the electrolyte. Several companies are working on these problems and if successfull the Metal-Air-Cell technology could become very interesting for a lot of applications. Already today this technology is used for commercial battery products such as batteries for hearing aids and high capacity (at low current) batteries for certain applications.

Future applications for Metal-Air-Cells include portable applications such as mobile phones as well as mobile applications such as electrical scooters and cars. Companies working on this technology you can find at fuel cell suppliers or the "Market-Analysis-Fuel-Cells".