Thermodynamics electrochemical cell assembly

Abstract The primary method for pH is based on the measurement of the potential difference of an electrochemical cell containing a platinum hydrogen electrode and a silver/silver chloride reference electrode, often called a Harned cell. Assumptions must be made to relate the operation of this cell to the thermodynamic definition of pH. National metrology institutes use the primary method to assign pH values to a limited number of primary standards (PS). The required comparability of pH can be ensured only if the buffers used for the calibration of pH meter-electrode assemblies are traceable to... 

Electrochemical stability of materials is the basis of safe behavior of a cell and any cell assemblies (batteries). Cyclic voltammetry can be used to evaluate the electrochemical stability window of materials. Thermodynamic stability of materials in intimate contact within the cell is desired but not always realized in high-voltage cells. Kinetic stability can be sufficient to design a working electrochemical cell. An example is the Li-oxyhalide catholyte primary battery in which a passivation layer forms on the lithium anode surfaces in the presence of neutral oxyhalide catholyte, and this layer provides separation between the two reactive electrode materials. An initially formed reaction layer of LiCl crystals protects the lithium metal from continued contact and further reaction. In acid catholytes, the passivation layer is dissolved immediately, producing heat that may cause a rapid increase in temperature. The same passivation layer in neutral solutions may result in deep reversals of the battery cell under rapid discharges (see Section 27.3.3). 

An electrochemical cell refers to an assembly in which a reaction system experiences an electrical potential that is applied across two electrodes. The electrodes can be metal or graphite or another conductor. The potential is externally controlled and is, therefore, another thermodynamic degree of freedom. We note this by adding 1 to the phase rule expression (Equation 4.11) for the degrees of freedom ... 

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