Application of impedance spectroscopy to electrochemical systems

Electrochemical impedance spectroscopy (EIS) and electrohydrodynamic (EHD) impedance spectroscopy were proved useful for studying electrochemical processes, as long as an adequate mathematical description of the system can be formed. Without such a model, impedance data can be difficult to interpret. An EIS and EHD-impedance study of the influence of coumarin on nickel electrodeposition is presented. A model that assumes adsorption of coumarin follows a Langmuir isotherm, that coumarin is consumed by incorporation into the deposit, and that metal-ion intermediates compete with the adsorbed leveling agent for surface sites is presented and shown to be in reasonable accord with EIS experiments. It is also discussed how EIS spectra may provide a more reliable means of determining kinetic parameters for the description of leveling agents rather than steady-state polarization experiments.; When EHD-impedance is employed, the low-frequency limit of the phase shift is found to be {dollar}180spcirc;{dollar} this indicates that the nickel-deposition rate decreases as the mass-transfer-limited flux of coumarin to the electrode increases. The proposed model successfully predicts variations in EHD spectra with disk rotation speed and current density but is less successful at predicting variations with the bulk coumarin concentration. The use of the EHD-impedance method for the determination of interfacial-kinetic and transport parameters relevant to models of leveling agents is demonstrated.; EHD-impedance was also used to study the influence of finite homogeneous reaction rates of the iodine/iodide redox system in the diffusion boundary layer. It was found that the iodine/iodide redox system is ideal for validating the EHD-impedance set-up if the iodine species is primarily present in the form of complexed {dollar}rm I{lcub}sb3sp-{rcub}.{dollar}; Lastly, a study of martensitic Fe-13Cr stainless steel revealed that its dissolution process is characterized by active, active-passive transition, and passive ranges. An EIS study was able to show that the dissolution process can be described by a continuous formation of a passive film at the electrode surface. Based on this finding, a simple model was able to describe both the main features of the steady-state and the EIS data in the active and active-transition ranges.