Kinetics of electrode processes at solid-state interfaces

In the first part of the thesis the concept of equilibrium potentials of the electrode, various types of potential existing at various inter-phases are presented. Modern theories of the electrodes are briefly reviewed. The experimental part of the thesis describes the construction, performance, and accuracy of a differential a.c. transformer bridge suitable for the Faradaic impedance measurements. The experimental cell and details of the preparation of the reference electrodes are described. Faradaic impedance measurements were made for the following systems System Concentration with supporting electrolyte 1. Hg/Hg 2. Ag/Ag 2 2+ + 3. Ag/AgX/X - 10 10 10 -6 -6 -6 N to 10 N to 10 N to 10 N XX 4. Ag/Agx/Ag 5. Ag/AgCl/Cl + - 10 10 -6 -6 N to 10 N to saturated XCl 6. Hg/Hg 2 X 2 /X - 10 -6 N to 10 N Hg XX 7. Hg/Hg 8. Hg/Hg 2 2 X 2 Cl /Hg 2 /Cl 2 2+ - 10 -6 N to 10 1 N to saturated XCl 9. Ag/AgX/X - , Glycerol 10 -6 N 10 N XX 10. Ag/AgX/Ag + , Glycerol 10 -6 -1 N to 10 -3 -3 -1 -1 -1 -2 -1 N Mg 2 N AgNO N AgNO N Hg 2 ( NO 3 3 ( NO 3 3 ) ) 2 2 N ( no supporting electrolyte ) 11. Hg/Hg 2 Cl 2 /Cl - 1 N to saturated ( no supporting electrolyte ) 12. Hg/Hg 2 Cl 2 /Cl - 1 N to saturated ( no supporting electrolyte ) The results were analysed to obtain the exchange current of all systems. From the studies of the variation of impedance with thickness of the film, it was possible to calculate the specific resistance and hence the diffusion constant for the interstitial silver ions. From the gradient of the Randles plot and knowledge of the diffusion constants, it was possible to obtain the concentration of interstitial silver ions in the silver halides at room temperature. Both diffusion constant and concentration of interstitial silver ions agree well with the values extrapolated from the high temperature data obtained by Wager and Jost. The equivalent circuit for the silver-silver halide electrode is proposed. It is shown that the two important elements are a faradaic impedance at the silver-silver halide interphase in series with another resistance associated with the building up of lattice, both being coupled. The behaviour of mercury-mercurous halide electrodes has been also studied. The optimum condition for good electrode performance is given with films of thickness prepared under these optimum conditions, the diffusion have contained entirely within the solid state. The thickness of the space charge within the solid phase has been calculated and the diffuse double layer has been evaluated