G. A. Ragoisha

Potentiodynamic electrochemical impedance spectroscopy. Copper underpotential deposition on gold

Copper underpotential deposition on polycrystalline gold was examined by potentiodynamic electrochemical impedance spectroscopy (PDEIS). The time evolution of the ac response was acquired as 3D plots of frequency response versus applied potential, and these data were later processed with an equivalent circuit analyser built into the virtual spectrometer. The dependences of the equivalent circuit parameters on potential revealed different responses of nitrate and sulphate. Nitrate adsorption pseudocapacitance, and the inverse of the adsorption pseudoresistance, both exhibited peaks in a narrow range of Cu monolayer growth, while sulphate affected a wider potential range and gave two desorption peaks in the anodic scan. Intrinsic irreversibility of the constituent processes was revealed by cyclic redox transformations of the Cu monolayer.

The Study of Thin Films by Electrochemical Impedance Spectroscopy

The capabilities and advantages of electrochemical impedance spectroscopy (EIS) as a useful and non-destructive technique are discussed. EIS provides the time dependent quantitative information about the electrode processes. The description of EIS is given in comprehensive way beginning from the theoretical basics of EIS and data interpretation in the frames of various equivalent electric circuits. The practical applications of EIS are described for the following thin film types: (i) cathodic metals/alloys films deposition; (ii) anodization of metals and characterization of oxide films and its growth by EIS including information provided by Mott-Schottky plots; (iii) underpotential deposition of metals; (iv) characterization of organic films onto metals; (v) application in development of biosensors and biofuel cells. The original data of EIS on cathodic electrodeposition of Co and Co-W are provided and reduction mechanisms involving adsorbed intermediates are discussed. The advantages of EIS in the oxide films characterization and their electrochemical properties are shown. EIS can be successfully applied for the characterization of biosensing surfaces and/or in evaluation of bioanalytical signals generated by biosensors. The glucose oxidase (GOx) based biosensor could be successfully analyzed by merged scanning electrochemical microscopy (SECM) and EIS techniques. Such combining study by SECM and EIS could be very attractive in order to evaluate the biofuel cell efficiency and in the modeling of biosensor action, because it is unavailable to obtain by other convenient electrochemical methods.

Underpotential shift in electrodeposition of metal adlayer on tellurium and the free energy of metal telluride formation

Underpotential deposition (UPD) of metals on polycrystalline tellurium film shows much similarity with UPD of metals on foreign metals, but the underpotential shifts on tellurium show no correlation with differences of work functions of the substrate and the deposited metal. In this work, we have evaluated the underpotential shifts of Pb, Cd, Zn, Bi, In, Sn, and Cu UPD on tellurium from cyclic voltammograms and potentiodynamic profiles of inverse charge transfer resistance derived from potentiodynamic impedance spectra, and shown a correlation of the underpotential shifts with the free energy of the corresponding metal telluride formation. The correlation can help to predict underpotential shifts for metals with complications in the measurement of this parameter.

Platinum electrochemical corrosion and protection in concentrated alkali metal chloride solutions investigated by potentiodynamic nanogravimetry

Platinum nanogravimetry potentiodynamic profiles in cyclic scans have shown significant dependence on alkali metal chloride concentration and effect of cations. Pt EQCM electrode mass drift in consecutive cyclic scans in 0.5 M LiCl, NaCl and CsCl was negative, similarly to the mass drift in aqueous solutions of H2SO4 with HCl additive, and this was due to electrochemical corrosion of platinum. The mass loss was prevented and inverted in 3 M solutions in the negative part of the scan, and the effect was attributed to shells of ion pairs firmly attached to the electrode surface via nonequilibrated Pt surface sites generated in the anodic scan. The increase in mass correlated with the increase in the Butterworth–van Dyke model resistance of quartz crystal resonator.

POTENTIODYNAMIC FREQUENCY RESPONSE OF ATOMIC LAYERS IN REVERSIBLE AND IRREVERSIBLE UNDERPOTENTIAL DEPOSITION

The potentiodynamic electrochemical frequency response of atomic layers underpotential deposition (UPD) shows different kinds of constituents in reversible and irreversible processes in a cyclic potential scan. The total response of reversible UPD decomposes into the constituent responses of double layer and Faradaic processes represented by adsorption capacitance and resistance in equivalent electric circuit (EEC). Anions that affect metal monolayer deposition give a separate RC branch in the EEC with characteristic R and C dependencies on the potential. The EEC of irreversible UPD does not contain adsorption capacitance. The Faradaic part of the response is revealed by charge transfer resistance and the Warburg impedance, showing hysteresis in cyclic scans. Nonideal double layer capacitance in the irreversible UPD is well represented by constant phase element.

Surface structures on non-metallic electrodes, catalysts of the oscillating anodic reactions

Abstract Ag + cathodic reduction at high overpotential on the surface of a conducting SnO 2 film and glassy carbon electrodes in the 10 13 –10 15 atoms cm −2 range gives stabilized aggregates of partly oxidized clusters and small Ag particles. Due to the effect of a surface compound (probably AgOH) and the excess free energy of small Ag particles, the non-equilibrium electrodeposits, unlike particles of the equilibrium Ag phase, exhibit an extremum in the catalytic activity dependence on the potential, which determines their capacity to catalyze anodic reactions in the oscillatory mode.