Energy Storage, 2nd Edition

Chapter 7Thermodynamics of Concentration Cells

Concentration cells are all “redox” in nature because, as is necessarily the case, the reduction and oxidation of chemical species occur within the device for the transference of energy. However, in this instance the redox label does not imply that these devices or cells are full flow electrolyte design with provisions for removing or replacing electrolytes. They are best operated as stationary (static) electrolyte systems. The particulars of design and physical configuration depend upon the intended applications. For example, it may be desirable to use close spacing between electrodes for higher power density application requirement devices, thus proportionately reducing their energy density.

7.1 Thermodynamic Background

The fundamental principles upon which the CIR system is based are probably best identified from the following thermodynamic considerations. Here, we quickly review some of the important and relevant thermodynamic functions upon which the analysis of cell behavior is based.

In order to arrive at the intended expression for the electrical potential of a CIR cell, we will begin with the familiar equation of state for an ideal gas:

(7.1)

where P and V are pressure and volume, respectively, of a quantity of gas consisting of n moles. T is temperature in degrees, absolute Kelvin, and R is the universal gas constant ...