Gas diffusion electrode

Gas diffusion electrodes are electrodes with a conjunction of a solid, liquid and gaseous interface, and an electrical conducting catalyst supporting an electrochemical reaction between the liquid and the gaseous phase. Especially known in fuel cells, where oxygen and hydrogen reacts at the gas diffusion electrodes into water, while converting the chemical bond energy into electrical energy. Usually the catalyst is fixed in a porous foil, so that the liquid and the gas can interact.

Besides these wetting characteristics, the gas diffusion electrode has of course to offer an optimal electric conductivity, in order to enable an electron transport with low ohmic resistance.

Last but not least the right choice of the catalyst is important too. In acidic electrolytes the catalysts are usual precious metals like Platinum, Ruthenium, Iridium and Rhodium. In alkaline electrolytes like zinc/air batteries one works usually with less expensive catalysts like carbon, manganese or silver.

Application

At first the gas diffusion electrodes have been designed for fuel cells. In the fifties of the last century the main fuel cell has been the Bacon type, converting carbon at high temperatures into electricity. Later the fuel cell research concentrates on the conversion of hydrogen, because of whose high reactivity. By the years the gas diffusion electrodes have been adapted for various other processes like:
* Zink/air battery since 1980
* Nickel-Metalhydrid battery since 1990
* Hydrochloric electrolysis starting in 2008
* Chlor-Alkaline-Electrolysis starting in 2009