V. V. Elkin

Electrochemical behavior of amorphous carbon films : kinetic and impedance-spectroscopy studies

Abstract Impedance spectra and potentiodynamic curves of oxidation and reduction reactions in the quinone/hydroquinone and Ce3+/4+ systems were measured in a 0.5M H2SO4 solution on amorphous carbon thin-film electrodes grown by magnetron sputtering or ion source techniques. The electrode equivalent circuit contains a constant phase element. Only narrow-bandgap (“graphitelike”) amorphous carbon is electrochemically active; however, the wider bandgap (“diamondlike”) material also acquires the activity on “doping” it with platinum (ca 10%) in the course of film growth. The admixture of platinum does not effect film conductivity; its action probably is of catalytic character. In its electrochemical activity, the platinum-containing amorphous diamondlike carbon films resemble boron-doped polycrystalline diamond.

Synthetic semiconductor diamond electrodes: elucidation of the equivalent circuit for the case of frequency-dependent impedance

Abstract Analysis of the frequency dependence of the impedance of boron-doped diamond thin film electrodes resulted in elucidation of their equivalent circuit. The latter generally comprises a frequency-independent capacitance (or a constant phase element) and a resistance, connected in parallel, with a series-connected “bulk” resistance. For electrodes whose impedance contains a constant phase element, a frequency-dependent Mott-Schottky plot enabled us to determine the flat-band potential. The constant phase element was shown to describe properties of the space charge region in diamond, rather than those of surface states. The behaviour of diamond electrodes is often affected by a series (“Helmholtz”) capacitance, which may be compared with the space charge capacitance of a semiconductor.

Synthetic semiconductor diamond electrodes: The comparative study of the electrochemical behaviour of polycrystalline and single crystal boron-doped films

Capacitance and potentiodynamic measurements were conducted on single crystal (homoepitaxial) and polycrystalline boron-doped diamond thin-film electrodes. The impedance characteristics and kinetic data in the Ce3+/4+ redox system, even if having a great deal of variability, appeared to be similar for the two kinds of diamond electrodes, whereas the kinetics of redox reactions on crystalline diamond and amorphous diamond-like carbon films differ significantly. These data in aggregate lead to a tentative conclusion that the electrochemical behaviour of polycrystalline diamond is determined by the diamond crystallites proper, rather than by the disordered carbon of the intercrystallite boundaries. The concentration of uncompensated acceptors in diamond was estimated from the linear and non-linear impedance data. The ways of presentation of Mott–Schottky plots for semiconductor electrodes are discussed for the case of frequency-dependent differential capacitance.

Synthetic semiconductor diamond electrodes : determination of acceptor concentration by linear and non-linear impedance measurements

The non-compensated boron concentration in thin films of boron-doped polycrystalline diamond, chemically vapour deposited onto tungsten or silicon substrates, was determined by the methods of differential capacitance and amplitude demodulation. In the case of frequency-independent capacitance, both methods give practically the same concentration value. For samples with frequency-dependent capacitance, an upper estimate of the concentration was obtained (using both methods) of the same order of magnitude. In this case, the electrode impedance includes a constant-phase element.

Interpretation of the Impedance Comprising Negative Capacitance and Constant Phase Elements on Iron Electrode in Weakly Acidic Media

The negative low-frequency capacitance that appears in interpretations of impedance of the iron electrode in weakly acidic solutions is shown to arise in the case of interaction of two consecutive nonequilibrium flows that constitute a two-stage anodic faradaic process of intermediate adsorption in the prepassivation potential range. The low-frequency capacitance is negative throughout a potential range where the logarithm of rate constant vs. potential (logk vs. E) dependence has the higher slope for the limiting stage. The low-frequency capacitance becomes positive at higher anodic potentials and for the other limiting stage.

Benzene Oxidation at Diamond Electrodes: Comparison of Microcrystalline and Nanocrystalline Diamonds

A comparative study of benzene oxidation at boron-doped diamond (BDD) and nitrogenated nanocrystalline diamond (NCD) anodes in 0.5 M K(2)SO(4) aqueous solution is conducted by using cyclic voltammetry and electrochemical impedance spectroscopy. It is shown by measurements of differential capacitance and anodic current that during the benzene oxidation at the BDD electrode, adsorption of a reaction intermediate occurs, which partially blocks the electrode surface and lowers the anodic current. At the NCD electrode, benzene is oxidized concurrently with oxygen evolution, a (quinoid) intermediate being adsorbed at the electrode. The adsorption and the electrode surface blocking are reflected in the impedance-frequency and impedance-potential complex-plane plots.

Application of nonlinear A.C. methods in the investigation of the electrical double layer properties

Abstract This paper presents the results of an investigation of the electrical double layer properties for the systems Hg/NaF, Cd/NaF, Hg/Na2SO4 carried out by use of nonlinear a.c. methods, based on the quadratic approximation of the current–voltage characteristic of the cell, the two-frequency method, and the amplitude demodulation method. By use of these methods it is possible to measure the potentials of zero charge of metals at higher electrolyte concentrations than is possible with the cell impedance measurement method.

Benzene oxidation at boron-doped diamond anode: An electrochemical-impedance spectroscopy study

Benzene oxidation at boron-doped diamond anode in 1 M KCl aqueous solution is studied by electrochemical-impedance spectroscopy method. The measurements of differential capacitance and anodic current showed that in the ideal polarizability region benzene does not adsorb at the diamond electrode (or its adsorption does not affect the electrode capacitance). At more positive potentials adsorption of an inter-mediate of the benzene oxidation occurs, which partially blocks the electrode surface and results in decrease of anodic current. Analysis of the shape of the complex-plane plots of impedance spectra points out to diffusion of part of the adsorbed intermediate into solution.

Electrochemical behavior of new electrode material: Compact of boron-doped synthetic diamond

Electrochemical properties of new electrode material—compact of boron-doped synthetic diamond—is studied for the first time. Cylindrical samples 3.5–4 mm in diameter and 2.5 mm in height were obtained by thermobaric processing of graphite–boron carbide mixtures in the diamond thermodynamic stability region (at the pressure of 8–9 GPa and temperature of ~2500 K). Their electrode behavior is studied using cyclic voltammetry and electrochemical impedance spectroscopy techniques. The cyclic voltammograms of the compact samples showed that their electrode characteristics are similar to those of traditional thin-film diamond electrodes obtained by the chemical vapor deposition (CVD) technique. In particular, they demonstrate rather wide potential window, low background current in indifferent electrolytes, and good reproducibility. It can be concluded that the diamond compacts practically are not inferior to the thin-film CVD-diamond electrodes and can serve as indicator electrodes, e.g., in electroanalysis. At the same time their compact form may be a convenience in the designing of electrolyzers and other electrochemical devices.

Characterization of CVD Diamond Thin Film Electrodes in Terms of their Semiconductivity

A series of boron-doped diamond films were grown using hot filament technique, over wide doping level ranges. Their semiconductor characteristics (the uncompensated acceptor concentration and flat band potential) were determined from Mott–Schottky plots measured by electrochemical impedance spectroscopy. These parameters can be used for the films’ characterization. The applicability of the electrochemical impedance spectroscopy approach in the semiconductor diamond characterization is discussed.