Expression of mixed potential

The same solid-gas interfaee can be the scene of multiple simultaneous and independent oxidation-reduction reactions. This has to be taken into consideration when modeling the electrical response of some electrochemical sensors, particularly those located in a gaseous atmosphere containing oxidant and reducing gases. 

We will approach this study by considering two electrochemical reactions of the following type  

The catalytic oxidation of carbon monoxide by oxygen on metallic oxide, is a typical example. 

Rideal s hypothesis, which supposes the presence of interactions between the adsorbed oxygen and the carbon monoxide, leads to  

Let us go back to the global system and consider separately the two reactions out of equilibrium. They are each at the origin of an electric current characterized by  

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