Oxidation potential oxygen fugacity

Until this point we considered the oxidation-reduction potentials of individual reactions between atoms of redox-couples, i.e., between two electrodes. They are no absolute measure of potential and do not allow comparing potentials of individual redox-couples between themselves. For such comparison it is necessary to have some common comparison electrode, which would play the role of the standard one. As any redox reaction may be conditionally presented with the participation of hydrogen or oxygen as donor or acceptor of electrons, these very common elements are used in this quality. In conditions of low temperature and pressure standard electrode of hydrogen is used and at high temperature and pressures - oxygen fugacity. 

The equivalent theoretical anode oxygen fugacity for hydrocarbon fuels is not set by a simple reaction equitibrium due to the complex reaction chemistry of these fuels. There are a large number of elementary steps, potential reaction pathways, and reaction intermediates. The most desirable reaction is the total oxidation of CH4 to CO2 and H2O, Eq. 3.2. This provides both the highest OCP value and represents full utilization of the fuel. If the catalyst is 100% selective for this reaction, the anode oxygen chemical potential will be set by this reaction equilibrium ... 

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