Ideal thermodynamically predicted voltage

Thermodynamics provides theoretical limits for fuel cell performance. The ideal cell voltage under standard state conditions (room temperature, atmospheric pressure, unit activities of aU species) is  

Actually, however, fuel cells are frequently operated under non-standard state conditions that vary greatly from the standard state. After analyzing how the reversible cell voltage varies with temperature, pressure, and activity, a full expression considering all the influencing factors can be written as  

This is known as the Nernst equation which is the centerpiece of fuel cell thermod)mamics. It is widely used in the calculation of the ideal cell voltage. 

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From thermodynamics, we can get the ideal voltage for a fuel cell. However, in practice, the actual cell voltage is less than the ideal thermodynamically predicted voltage due to irreversible losses, even when the open circuit voltage is measured. Normally, the losses can be broken up into three major types activation losses, ohmic losses and concentration losses. The real cell voltage can thus be written as below ... 

Chapters 7 to 9 apply the thermodynamic relationships to mixtures, to phase equilibria, and to chemical equilibrium. In Chapter 7, both nonelectrolyte and electrolyte solutions are described, including the properties of ideal mixtures. The Debye-Hiickel theory is developed and applied to the electrolyte solutions. Thermal properties and osmotic pressure are also described. In Chapter 8, the principles of phase equilibria of pure substances and of mixtures are presented. The phase rule, Clapeyron equation, and phase diagrams are used extensively in the description of representative systems. Chapter 9 uses thermodynamics to describe chemical equilibrium. The equilibrium constant and its relationship to pressure, temperature, and activity is developed, as are the basic equations that apply to electrochemical cells. Examples are given that demonstrate the use of thermodynamics in predicting equilibrium conditions and cell voltages. 

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