Catalysts electron supply

The observed increase in CH formation and simultaneous decrease in CO formation with increasing catalyst potential and work function i.e. with increasing supply of O2 to the catalyst is remarkable and can be attributed to the preferential formation on the Rh surface of electron donor hydrogenated carbonylic species leading to formation of CH4 and to the decreasing coverage of more electron acceptor carbonylic species resulting in CO formation.59... 

The enhancement in the catalytic activity is due to the electrochemical supply of H+to the catalyst which decreases the catalyst work function and thus strengthens the chemisorptive bond of electron acceptor N while at the same time weakening the bonds of electron donor H and NH3. 

In electrochemical systems, not only the reactant species but also electrons must be supplied to and/or withdrawn from the catalyst particles, since the electrons are directly involved in all electrochemical reactions. 

Most often, these disperse metal catalysts are supported by an electronically conducting substrate or carrier that should provide for uniform supply or withdrawal of electrons (current) to or from all catalyst crystallites. The substrate should also serve to stabilize the disperse state of the catalyst and retard any spontaneous coarsening of the catalyst crystallites. Two situations are to be distinguished (1) the disperse metal catalyst is applied to a substrate consisting of the same metal, and (2) it is applied to a chemically different substrate (a foreign substrate). Platinized platinum is a typical example of the former situation. 

The function of the electrolyte membrane is to facilitate transport of protons from anode to cathode and to serve as an effective barrier to reactant crossover. The electrodes host the electrochemical reactions within the catalyst layer and provide electronic conductivity, and pathways for reactant supply to the catalyst and removal of products from the catalyst [96], The GDL is a carbon paper of 0.2 0.5 mm thickness that provides rigidity and support to the membrane electrode assembly (MEA). It incorporates hydrophobic material that facilitates the product water drainage and prevents... 

An effective catalyst layer must serve multiple functions simultaneously electron and proton conduction, oxygen or hydrogen supply, and water management. The composition and structure of a CL can affecf all fhese functions... 

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