Nernst equilibrium cell voltage, concentration

CONCENTRATION DEPENDENCE OF EQUILIBRIUM CELL VOLTAGE THE GENERAL NERNST EQUATION... 

Equation (5.9) is the general Nernst equation giving the concentration dependence of the equilibrium cell voltage. It will be used in the next section of this chapter to derive the equilibrium electrode potential for metal/metal-ion and redox electrodes. 

Experiments involving the Nernst equation are primarily concerned with concentrations. One or more of the concentrations in the Q portion of the Nernst equation are calculated by measuring the nonstandard cell potential and comparing this to the standard cell potential. Remember, you calculate the concentration from a measured voltage. Once the concentration is determined, it may be combined with other concentrations and used to calculate an equilibrium constant. 

The SOFC consists of cathode, electrolyte and anode collectively referred to as the PEN - positive electrode, electrolyte, negative electrode. A single cell operated with hydrogen and oxygen provides at equilibrium a theoretical reversible (Nernst) or open circuit voltage (OCV) of 1.229 V at standard conditions (STP, T = 273.15 K. i> = 1 atm). With the standard electrode potential E°, universal gas constant R. temperature T. Faraday s constant F, molar concentration x and pressure p, the OCV is given by... 

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... 

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