Linear sweep voltammetry at the tubular graphite electrode: Part II. Totally irreversible processes

The theory of linear sweep voltammetry at the tubular graphite electrode has been developed for irreversible processes. The convective diffusion differential equations have been transformed into an integral equation which is solved numerically. The current-potential curves have been calculated theoretically and verified experimentally. The dependence of the current-potential curves on velocity has been studied. A procedure for the determination of kinetic parameters, i.e. standard rate constant and transfer coefficient, is presented.     

Photogalvanic cells: Part VIII. The theory of the transparent rotating disc electrode

The theory of the transparent rotating disc electrode is first extended to cover the case where two photogenerated species react with second-order kinetics and where one of the species is electroactive and the other is not. Secondly the theory is developed to describe the case where the solution is bleached close to the electrode. Thirdly theory is presented for experiments where the light source is modulated and the phase shift and amplitude of the resulting modulated photocurrent are measured.     

Hydrodynamic voltammetry at channel electrodes: Part IV. Theory of chronopotentiometry for reversible electrode reactions

The theory of chronopotentiometric measurements at channel electrodes is developed for reversible electrode reactions, by rigorously solving the corresponding time-dependent boundary value problem, where the non-uniform accessibility of the channel electrode surface is taken into consideration. The theoretical equations of the transition time and the potential-time curve are derived as functions of (I_d/I), where I denotes the applied current intensity and I_d the limiting diffusion current obtained at steady-state. Finally, the time variation of the current density distribution at the electrode surface is given.     

Hydrodynamic voltammetry at channel electrodes: Part II. Theory of first-order kinetic collection efficiencies

The theory of first-order kinetic collection efficiencies at the double channel electrode is developed for the following two schemes: (I) A±n₁e→B (at the generator electrode), B→^kP (in solution), B±n₂e→Y (at the detector electrode), (II) A±n₁e→B, B→^kA, B±n₂e→Y. The exact expressions for the kinetic collection efficiencies are obtained as ascending and asymptotic series with respect to the kinetic parameter. Further, approximate formulae in exponential forms are given, which hold within an error of about 2% for conventional electrode geometry. Finally, the validity of the approximate procedure, which has been used previously to obtain the kinetic collection efficiencies for fast homogeneous reactions, is discussed in comparison with the present theory.     

Voltammetric study of humic and fulvic substances: Part II. Mechanism of reaction of the Pb-fulvic complexes on the mercury electrode

A model is presented for the electrode process corresponding to the reduction of Pb(II) complexed by fulvic substances. The various factors which may affect the polarographic results are discussed and a mathematical expression is given for the polarographic wave. The influence of various parameters was tested. It was found that the formation of complexes both present in solution and adsorbed at the surface of the electrode is the predominant factor which affects the potential of the wave. Moreover, the diffusion coefficient of the complexes is much lower than that of free lead. We discuss the nature of the complexes adsorbed at the electrode surface and the implications of the findings of this work when using the polarographic methods for the determination of the complexing ability of waters.     

Characteristics of the dropping mercury electrode below the limiting current: Part II. Drop time and scan rate effects

A mathematical model of the dropping mercury electrode that includes the effects of electrochemical kinetics, ohmic potential drop, and mass transfer is used to examine the influence of scan rate and drop time on the shape of the polarographic wave. The system behavior is described in terms of three characteristic dimensionless parameters. For certain parameter values, the half-wave potential predicted for a metal deposition reaction is dependent on the drop time and scan rate used to obtain the polarogram.     

Voltammetry at partially covered electrodes: Part II. Linear potential sweep and cyclic voltammetry

Effect of inhomogeneity of the electrode surface on the linear potential sweep and cyclic voltammograms is investigated theoretically and experimentally using model electrodes partially covered with photoresist layer. Good agreement between the theoretical and experimental results is obtained.     

Supramolecular phenomena in organic redox films at electrodes: Part I. The methylene blue/leucomethylene blue redox couple at the platinum electrode

It is possible to generate conductive multilayer structures by reduction of methylene blue cations at the interface: clean surface of a platinum electrode/1 M aqueous electrolyte solution.The characteristics of the multilayer ordered phase generated in fluoride and nitrate solutions are presented and the mechanism of a fast charge transfer between electrode/organic film and organic film/aqueous solution interfaces is discussed. The conductivity of the film is interpreted by postulating formation of a mixed valence structure with the generation of a cation radical intermediate which is favoured in the solid state at characteristic potentials.     

Polarography with controlled current density — Chronopotentiometry at a dropping ellectrode: Part III. Experimental verfication of the theory

A large number of experiments have been communicated with regard to the operation of a polarograph which shows essentially a galvanostatic character instead of the usual potentiostatic one. A reasonable good agreement could be established between practice and theory. Finally some introductary experiments have been reported concerning phenomena connected with the absence of surfactants in the solution, and other ones observed in the presence of catalysts which promote the evolution of hydrogen.     

Voltammetry at microcylinder electrodes: Part III. Chronopotentiometry

Expressions for chronopotentiometry at stationary microcylinder electrodes are presented. The transition time, τ, is expressed as a function of a single parameter λ ( = nFc^*_RD / ia, where a is the radius of the electrode, D is the diffusion coefficient, i is the current density, n is the number of transferred electrons, F is the Faraday constant and c^*_R is the bulk concentration. When the values of λ are small, the transition-time constant, i√τ / c^*_R, depends linearly on λ, with the intercept predicted from the Sand equation. Conversely, when values of λ increase, the transition time also increases exponentially. Therefore transition necessarily occurs no matter how small a current flows. An approximate equation for the transition time is presented, from which one can evaluate the diffusion coefficient. Equations for the potential-time curve and the quarter-wave potential are also obtained. The equations were tested experimentally using carbon fiber electrodes (a = 4.1 μ m) and platinum wire electrodes (a = 10-100μ m). The transition times obtained experimentally were in good agreement with those predicted theoretically for various values of the applied current, for several different radii of the electrodes.     

Voltammetry at partially covered electrodes: Part I. Chronopotentiometry and chronoamperometry at model electrodes

Equations for chronopotentiometry and chronoamperometry at partially covered electrodes have been derived using a model of hexagonal array of cylidrical spaces terminated, at the electrode surface, by concentric active and inactive regions. The boundary value problem was shown to be analogous to that for a charge transfer preceded by a chemical reaction. Experiments with the reduction of ferricyanide on gold model electrodes partially covered with photoresist layer showed excellent agreement with the theory. Application of the equations to estimation of coverage and size of active sites distributed on a electrode surface is discussed.     

Hydrodynamic voltammetry at channel electrodes: Part VII. Current transients at double channel electrodes

Expressions for the transient current at the downstream electrode in response to galvanostatic electrolysis at the upstream electrode in the channel flow cell were derived by applying double Laplace transformation when the electrode reaction at the upstream electrode is kinetically controlled. The ratio of the transient current to the steady state current or the transient collection efficiency was calculated as a function of electrode geometry and θ

, where U_m is the mean flow velocity in the channel cell, D the diffusion coefficient of the electroactive species, b the half height of the channel, x₁ the length of the upstream electrode and t the time elapsed since the beginning of the galvanostatic electrolysis at the upstream electrode. Curves for the transient collection efficiency can be applied to evaluating the amount of adsorption at the upstream electrode when metal at the electrode is anodically dissolved in solution. Digital simulation was carried out. Transient curves, obtained analytically, were in good agreement with those evaluated from the digital simulation. In order to allow one to draw transient curves readily, we derived a simple approximate equation.     

Non-stoichiometric molybdenum oxides as cathodes for lithium cells: Part II. Secondary batteries

Mo₄O₁₁, Mo₈O₂₃ and Mo₉O₂₆ have been examined as cathodes for secondary lithium cells. These oxides can form ternary phases from which Li⁺ can be almost quantitatively recovered on charge, for limited e/Mo values (e.g. 0.8 for Mo₈O₂₃). Higher values of e/Mo make the reduction process irreversible due to the destruction of the original lattices. Cyclic voltammetry experiments have shown that these oxides can maintain their reversible behaviour for many cycles, provided the cathodic scanning is limited. Cycling of prismatic Li/Mo₈O₂₃ cells has confirmed that this oxide can behave reversibly with good voltage retention even at discharge depths near the limiting value.     

Hydrodynamic voltammetry at channel electrodes: Part III. Theory of kinetic currents

A theory of kinetic currents at a channel electrode is developed without any assumption on the magnitude of the rate constant of the preceding chemical reaction. An approximate equation with reasonable accuracy which relates the limiting current to the rate constant, flow velocity and the electrode geometries, is presented. The validity of the equation derived from the concept of the thin reaction layer is also discussed.     

Solvent effect on standard electrode potential: Part II. Silver-silver bromide electrode in methanol-water mixtures

The standard potentials of the silver-silver bromide electrode have been determined over a broad range of methanol concentrations from e.m.f. measurements of the cell Pt, H₂(g, 1 atm); HBr(m), X% methanol, Y% water; AgBr, Ag at eight temperatures ranging from 20 to 55°C. The standard e.m.f. has been expressed as a function of temperature. Thermodynamic functions of cell process, the primary medium effect of various media on hydrobromic acid, and thermodynamics of transfer of HBr from water to methanolic media have been computed and discussed in the light of ion-solvent interactions as well as the structural changes of the solvents.     

Thermal and chromatographic behaviour of metal complexes. Part II. Complexes of platinum(II) with dipeptide ester

Experimental measurements of the rate of reduction of particles of Carol Lake and Kiruna ores have been made using pure hydrogen and pure carbon monoxide and mixtures of these two gases. The temperature range covered was 773–1143 K and throughout this range the reduction rate with hydrogen was greater than that with carbon monoxide. A retracting core model was found to best fit the experimental data even when granules of 9 × 10^?4 m diameter were used. Reduction with gas mixtures of hydrogen and carbon monoxide give rates intermediate between those of the pure gases.     

Anodic stripping voltammetry in a flow-through cell with a fixed mercury film glassy carbon disc electrode. Part I

Anodic stripping voltammetry at a glassy carbon disc electrode covered by a thin mercury film was adapted for use in a flow-through cell. The resulting system is characterized by extreme simplicity of set-up and operation, high sensitivity and excellent precision and stability. Its performance was tested via the determination of hydrated or labile complex ions of heavy metal ions in sea water, using short (2–10 min) deposition periods. The dependence of the stripping peak charge on metal ion concentration, length of deposition period, solution flow rate and other variables was examined and the reliability of the results obtained were evaluated under conditions resembling continuous monitoring.