Fuel-cell-type oxygen reduction electrodes

CCEs for Fuel-Cell-Type Oxygen Reduction Electrodes... 

Gas electrodes are electrodes that are used for high current density conversion of reactants that are snpplied from the gas phase. Perhaps the most important of these reactions are hydrogen oxidation and oxygen reduction, which are carried out in electrochemical fuel cells. But fuel cell type hydrophobic gas electrodes are also used in batteries, gas sensors and for electromachining. 

Regardless of the specific type of fuel cell, gaseous fuels (usually hydrogen) and oxidants (usually ambient air) are continuously fed to the anode and the cathode, respectively. The gas streams of the reactants do not mix, since they are separated by the electrolyte. The electrochemical combustion of hydrogen, and the electrochemical reduction of oxygen, takes place at the surface of the electrodes, the porosities of which provide an extensive area for these reactions to be catalysed, as well as to facilitate the mass transport of the reactants/products to/from the electrolyte from/to the gas phase. 

The monolithic structure, good mechanical strength, high surface area, and electrical conductivity of these carbon materials make them attractive as electrodes for various electrochemical applications. As hydrogen oxidation (or oxygen reduction) catalysts may be incorporated to such porous materials, one specific application to consider is the use of this type of material as alkaline fuel cell electrode. 

The membrane in the polymer electrolyte fuel cell (PEFC) is a key component. Not by chance does the type of membrane brand the cell name - it is the most important component determining cell architecture and operation regime. Polymer electrolyte membranes are almost impermeable to gases, which is crucial for gas-feed cells, where hydrogen (or methanol) oxidation and oxygen reduction must take place at two separated electrodes. However, water can diffuse through the membrane and so can methanol. Parasitic transport of methanol (methanol crossover) severely impedes the performance of the direct methanol fuel cell (DMFC). 

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