Electrochemical Technique

Measurement of emf of a suitable electrochemical cell is one of the most useful methods of obtaining thermodynamic data. It is now well established that if the electrochemical cell satisfies the condition of reversibility, reactions at the electrodes are well defined and the electrolyte conducts exclusively through ions, the change in free energy of a reaction on passing one Faraday of electricity is related to the emf of the cell by the expression: ΔG =  − nFE. Depending on the overall chemical reaction the cells are categorized into displacement, formation and concentration cells. The emf of these cells must be reversible and true representative of the correct cell reaction. To ascertain the correct and accurate value of the emf theoretical considerations as well as criteria of reversibility of the cell have been very effectively discussed in this chapter. The utility of aqueous, fused salts and oxide melts and solid electrolytes in the measurement of thermodynamic properties of alloys and compounds has been discussed with selected examples. Solid electrolytes have some distinct advantages over fused salts. Due to the refractory nature of many solid electrolytes these can be used at much higher temperatures. There are, however serious limitations restricting the use of solid electrolyte. Only solids exhibiting predominantly ionic conductivity (tion ≥ 0.99) over a useful range of temperature and chemical potential are considered to be a good electrolyte. Thus it becomes essential to know the extent of contribution of ionic and electronic conductivity in a solid under the changing experimental conditions to consider their use in the formation of a galvanic cell. Construction of galvanic cell assemblies for holding fused salt as well as solid electrolytes have been discussed. Various electrolytes and system investigated by both types of electrolytes are listed.