Oxygen concentration cell Nernst equation

At operating temperature (100-400°C), the oxygen anions have sufficient mobility in the solid electrolyte. The cell voltage ECeii is then related to the partial pressure of oxygen by the Nernst equation written for the concentration cell. 

At this time, electromotive force is generated. Therefore, it is called an oxygen concentration cell. The electromotive force is given by the Nernst equation ... 

In the most general way, one can express the thermodynamic cell potential of an SOFC as the cell potential of an oxygen concentration cell using the Nernst equation ... 

A higher polarization curve when cell operating pressure is increased can be expected on the base of the Nernst equation (3.15), but the concomitant increase of / o, due to the higher concentration of reactant gases on electrodes, with the consequent improvement of the hydrogen/oxygen reaction rate, has to be also considered [34]. 

An oxygen pumping cell operates by active pumping of 02 ions from the negative to the positive electrode when an electrical charge is applied. To adjust a fixed O2 concentration in a cavity, a certain electrical charge has to be applied (EMF). This electromotive force (E) is described by the Nernst equation. 

This reasoning is incorrect. The Nernst equation describes the dependence of OCV on the oxygen concentration only at equilibrium. This equation is not applicable in the situation when the cell generates current. Thus, Eq. (3.12) does not represent any real voltage loss in a cell. A true voltage loss in non-equilibrium conditions can be calculated from the kinetic equations as discussed above, this leads to the transport loss in the form Vconc = In Note that in Eq. (3.12) the factor is BT/ nF), while in the... 

Increasing the reactant concentration has a minor effect on the thermodynamics of the reaction (due to the logarithmic form of the Nernst equation), but it can have a significant benefit on the kinetics of a reaction (hnear). For this reason, fuel cells are often operated on pure oxygen as the partial pressure of oxygen in air is only 0.2, and so the exchange current density is reduced when operating with air. 

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