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An atypical example of the effect of the self-induced convection on the morphology of current-potential responses was described, for the case of the parallel electroreduction of some metal cations (Cd 2+ , Cu 2+ , Zn 2+ and Eu 3+ ) and H + ions at the mercury electrode. Separation of the individual faradaic contributions from the metal ions and hydrogen ions reduction, made with the double potential-step chronocoulometry, and based on the difference between the rates of these processes, allowed us to find that the total faradaic current exhibits negative or positive deviations from the sum of individual faradaic currents. In order to diagnose the origin of this anomaly, the series of experiments for various acid concentrations, electrolysis times and the electrode types/geometries, including the hanging mercury drop and the mercury film electrodes, were performed. The results obtained indicated that the observed anomalies are due not to the surface blocking or latent limiting currents, but due to a rather novel mechanism that involves convective instabilities which accompany the hydrogen evolution reaction. The resulting change of the concentration distribution of all species involved in the electrode process appropriately changes the individual contributions from the faradaic currents. These studies show one more role of convection in electrochemical systems.

Hydrogen peroxide generation R&D data obtained in an alkaline fuel cell-type electrochemical reactor with a dividing Nafion™ 117 membrane have been used to extract anion-conducting properties of the cation-exchange membrane. The effective diffusion coefficient of NaOH and the average transport number of OH − in the membrane were obtained by fitting a model formula for the total alkalinity of outlet catholyte to experimental alkalinities obtained with various electrolysis parameters’ values. The formula resulted from assumptions that NaOH diffuses through the membrane and OH − migrates through the membrane, and that HO 2 − does not penetrate the membrane. The membrane parameters extracted in this way were in good agreement with similar data reported by others for Nafion™. Hydrogen peroxide current efficiencies remained over 90% and H 2 O 2 concentrations reached 7 wt.%, however the fuel cell reactor's electrical efficiency was strongly limited by high internal resistance.

Electrochemical and electrochemical quartz crystal microbalance (EQCM) methods were used for the analysis of the growth and dissolution processes of sparingly soluble deposits. As a model of a sparingly soluble film, uranyl-hexacyanoferrate was selected. Additionally the rate of Prussian blue deposition was studied. We have shown that coupling of the EQCM technique with standard electrochemical methods may be useful in the study of mechanisms of electrodeposition phenomena when the solubility of the product of the electrode reaction is limited. The transformation of mass–time data into current–time dependences allows an analysis of the reaction in terms of electrocrystallization steps while other masking processes are superimposed during the polarization of the electrode. This approach may have general value and may be applied not only to hexacyanoferrate deposition but also to deposition of other products of the electrode reaction, which exhibit limited solubility. Analysis of growth of uranyl-hexacyanoferrate on the Au/quartz electrode under potentiostatic and cyclic voltammetry conditions, taken as an instance, reveals that the first step, limited by the growth of the crystallization nuclei, is clearly separated from the uniform growth, limited by diffusion. For thicker films, the slope of the frequency–charge dependence is dominated by the insertion/removal process of potassium ions, to and from the film. During the dissolution of the uranyl-hexacyanoferrate deposits, two clearly separated steps were observed. During the first, relatively fast oxidation of the deposit is observed which is accompanied by removal of potassium ions from the film. The second step corresponds to a chemical dissolution of the oxidized film. The rate coefficients corresponding to both steps were determined. Based on the gravimetric and electrochemical data, the molar mass of the deposited uranyl-hexacyanoferrate was estimated as equal to 690 ± 90 g/mol. From these and the EDX data, a chemical formula of the deposited uranyl-hexacyanoferrate was proposed as: K2(UO2)[Fe(CN)6].

The electrochemical behaviour of mixtures of phenazine (P) with iodine (I2) in the solid state was investigated. Three types of electrochemical experiments were conducted: (i) EMF measurements of the Ag/AgI/I2:P system for various I2 : P ratios, (ii) cyclic voltammetric (CV) experiments and (iii) potentiometric measurements of the open cell potentials after different cathodic charges were injected into the I2 : P pellets. In the first case, a detailed analysis of the observed electromotive force was presented. The Gibbs free energy of the I2 : P complex determined was in good agreement with earlier results. In the second case, the CV curves corresponding to the electrode processes of phenazine mixed with graphite in the solid state indicate that the mass and charge transfer, which occur in the pellets, are faster than expected. The potentiometric experiments confirm this conclusion. Additional experiments, conducted with pellets of different thickness, indicate that although, in comparison with an equilibrated pellet, the concentration profiles are modified in small layers (diffusion layers) neighbouring the electrodes, the electrode reaction probably occurs in the whole pellet. A tentative mechanism of these processes is discussed. Copyright © 2003 John Wiley & Sons, Ltd.

The properties of a cobalt amalgam formed during electrochemical reduction of Co(II) ions at mercury electrodes were investigated by cyclic voltammetric and chronocoulometric methods. Experiments were performed in a range of temperatures from −20 to 75°C, and a wide range of Co(II) concentrations, in NaClO 4 solutions of various concentrations. At lower temperatures and low cathodic charges of Co(II) reduction, a homogeneous cobalt amalgam is formed, which undergoes a rather fast deactivation, leading probably to a Co 3 cluster. The cluster is not electroactive in the accessible range of potentials. At higher concentrations of Co(II) and at higher temperatures, on anodic waves corresponding to oxidation of cobalt amalgam and recorded in unbuffered solutions, up to four oxidation steps are observed. On the other hand, in acetic buffer solution (pH 3.6), under chronocoulometric conditions, only one oxidation peak appears. Thus, other oxidation steps could be ascribed to the oxidation of Co(II) to Co(III) hydroxide. The formal potential, the rate constant at this potential, and the Tafel slopes (anodic- αn , and cathodic- βn ) corresponding to the electrode process Co(II)+2e − +Hg=Co(Hg) were determined at 253 K. Determination of these parameters at higher temperatures was impossible, due to fast deactivation of the cobalt amalgam.

Two limiting-case simplified models of mass- and charge-transport phenomena in a flow-through electrochemical reactor were developed. It is postulated that the true experimental system's behavior falls in between. The models account for energy loss due to the ohmic drop, forced convection, diffusion, and migration. The calculation results were compared against experimental data.

The temperature dependences of the four transfer coefficients for cathodic and anodic electrode reactions of two different types of systems, namely Cr(III)/Cr(II) and Cr(II)/Cr(Hg), were determined in 5.0 M NaClO 4 solution. The results were obtained for a wide range of temperatures from −20 to 90°C. The α parameter determined from the log k fh on E dependence corresponding to the Cr 3+ +e − →Cr 2+ electrode process shows the highest dependence on temperature (∂ α /∂ T =1.1±0.3×10 −3 K −1 ), whereas the β parameter corresponding to the Cr 2+ →Cr 3+ +e − electrode process is virtually independent of temperature (∂ β /∂ T =0). The same results were obtained when the transfer coefficients were determined from dependence of the enthalpy and entropy of activation on overpotential. The observed temperature dependence of α is attributed to the changes of the ϕ 2 potential. The transfer coefficients for the Cr 2+/0 electrode reaction also show some dependence on temperature (∂ α /∂ T =8.7±2.0×10 −4 K −1 and ∂ β /∂ T =3.2±1.4×10 −4 K −1 ), which probably results from the influence of the ϕ 2 potential.

Oxidation of a homogeneous chromium amalgam and homogeneous Cr–Zn, Cr–Mn, Cr–Tl, Cr–Pb, and Cr–Cu amalgams were investigated by the double potential-step chronocoulometric method. Experiments conducted with various concentrations of chromium in mercury confirm our earlier results, showing de-activation of the chromium amalgam. In the presence of Zn and Tl, no change in oxidation of the chromium amalgam was observed. In the presence of other metals (Mn, Pb and Cu), oxidation of the chromium amalgam was less efficient than in the absence of these metals. We interpret our experimental data in terms of high-spin Cr atom formation (with electronic configuration 3d 5 4s 1 ), and fast Cr–Cr molecule formation. Since the dissociation energy of Cr 2 is 142±5 kJ mol −1 , it is electrochemically inactive in the potential range investigated. In the case of the Cu–Cr amalgam, de-activation of the chromium amalgam was higher than in the cases of Pb–Cr and Mn–Cr. We interpret this as a result of a higher interaction energy of the Cu–Cr compound, than that of the Cr 2 . From literature data it follows that the dissociation energy of the Cu–Cr compound is, indeed, higher, being ca. 150 kJ mol −1 .

Electroreduction of chloramines (H2NCl, HNCl2 and NCl3) at the platinum electrode was investigated in aqueous solutions of varying pH. The two former compounds are reduced irreversibly and their cathodic peak potentials are pH dependent (Epc (H2NCl)=−0.25 to −0.15 V (pH 7–4), Epc (HNCl2)=0.35–0.45 V (pH 4.5–2.5), at scan rate ν=0.05 V s−1). Trichloramine is reduced at the same potential at which Cl2 is formed, and the whole system is reversible. From the dependence of cathodic peak potentials on pH the protonation equilibrium constants of H2NCl and HNCl2 were determined. They were found to be (pK) 6.4±0.1 and 3.41±0.05, respectively. The extinction coefficients of protonated species are lower than that of non-protonated ones. The formal potential of the electrode reaction: NCl3+4H++6e−=NH4++3Cl− extrapolated to pH 0 equals 1.44 V (pH 0, SHE), thus the Gibbs energy of formation of NCl3, ΔGf=362.1 kJ mol−1.

The kineticsand mechanism of the electrode process Cr II ) + 2e − = Cr(Hg) was investigated in LiBr + LiClO 4 solutions having constant water activity equal to 0.764. The concentration of LiBr was changed from 0 to 4.0 M. On the basis of the results obtained, the equilibrium constant of the CrBr + complex ( K 1 = 0.3 ± 0.1 M) was calculated. This value is higher than that of the chloride and lower than that of the iodide complex, which proves that the Cr 2+ ion is a soft cation. During electroreduction of the Cr 2+ ion in solutions of different water activity in the presence and in the absence of bromide ions, the following cathodic reaction orders were observed: −7.2, −5.9 and −1 for water in the absence of bromide ions, water in the presence of bromide ions and bromide ions, respectively. Since the hydration number determined was equal to 9.2 in bromide-free solutions, therefore the complex which undergoes a direct reduction at the electrode is weakly hydrated Cr(H 2 O) 2 2+ . A comparison of the rate constants of the Cr(II)|Cr(Hg) electrode reaction in solutions of perchlorate, chlorides, bromides and iodides, with various water activity reveals that the water activity is the most important factor which determines the rate constant of this process.

The formal potentials and kinetic parameters for the electrode process Cr2+ + 2e−⇄Cr0 occurring at mercury electrode in solutions of LiClO4 + LiCl(aH2O = 0.741) and LiClO4 + LiI(aH2O = 0.853) were determined from analysis of irreversible anodic and cathodic chronocoulometric charge-potential curves. The interaction of Cr(II) with I− ions was found to be stronger (K1 = 1.6 M−1) than the very weak interaction with Cl− ions (K1 < 0.1 M−1). Double-layer properties were established for the solutions studied. On the basis of the rate constants, transfer coefficients, electrode reaction orders, double-layer properties and charges of the activated complex determined, a mechanism for the electrode reaction of the Cr2+/Cr(Hg) redox couple was proposed.

Impedance spectroscopy was used to measure the properties of the gold electrode in 0.5 M H 2 SO 4 solution in the double-layer region (−0.25 to 1.05 V vs. sodium chloride saturated calomel electrode (SSCE)) and the region of oxide monolayer formation (1.05–1.4 V vs. SSCE). The dependence of the capacitance on potential was analysed. In both regions equivalent circuits composed of a resistor corresponding to the resistivity of the solution and a capacitor were proposed. It was found that in the double-layer region the capacitance reflected the properties of the pure gold electrode, whereas in the oxide region it depended on the coverage of the surface, corresponding partially to pure gold, MOH dipoles, oxide or a reconstructed gold surface. The improvements made by introducing a constant phase element instead of the capacitor and adding a parallel resistor in the oxide region were analysed. The roughness of the gold electrode was also estimated. The results obtained by impedance measurements were complemented by voltammetric studies to clarify the process, to confirm the measured values and to explain the meanings of the calculated parameters.

The influence of temperature over the range from −30 to 25°C on the electrochemical properties of solid iron(III) hexacyanoferrate(II/III) containing various amounts of water has been studied by means of cyclic voltammetry and impedance spectroscopy. The system studied is a water-insoluble mixed-valence coordination compound. The experiments have shown in major role for water molecules in the charge transport across this solid system. An attempt has been made to understand the experimental data on the basis of an existing model of redox conductance in solid mixed-valence transition metal hexacyanoferrates. The activation energy of charge migration in a partially dehydrated system and the activation energy of charge diffusion in a well-hydrated system have been determined.

Graphite electrodes intercalated with various metals (Ni, Co, Pd, Pt, Rh, and Ru) have been bonded with an inorganic polymer and used as cathodes in the hydrogen evolution reactions (HER) in . Four of the most active electrodes showed very good mechanical and electrochemical stability. The overvoltage of the HER at decreased in the following order: −525 mV, for pure graphite and −254, −137, −103, and −58 mV, for the Pd/C, Rh/C, Pt/C, and Ru/C electrodes, respectively. The kinetics of the HER for two electrodes (Ru/C and Pd/C) were measured with the use of an ac impedance technique. In both cases, the HER proceeds via the Volmer‐Heyrovsky mechanism. The results obtained proved that the Pd/C electrode had a larger active surface area than the Ru/C one did.

The effect of tensioactive agents (TSA = SDS, BRIJ35, BRIJ78, BRIJ99, and CTAB) on the kinetics of hydrogen evolution at a rotating nickel electrode in 0.2 M solutions of Na2SO4 was investigated. It was found that at higher concentrations of TSA, their presence inhibited the reaction although their adsorption behaviour at the nickel electrode is different. We concluded that BRIJ35 and CTAB should show better performance in the hydrogenation of organic compounds than SDS.

Graphite electrodes intercalated with various metals (Ni, Co, Pd, Pt, Rh, and Ru) have been bonded with an inorganic polymer and used as cathodes in the hydrogen evolution reactions (HER) in . Four of the most active electrodes showed very good mechanical and electrochemical stability. The overvoltage of the HER at decreased in the following order: −525 mV, for pure graphite and −254, −137, −103, and −58 mV, for the Pd/C, Rh/C, Pt/C, and Ru/C electrodes, respectively. The kinetics of the HER for two electrodes (Ru/C and Pd/C) were measured with the use of an ac impedance technique. In both cases, the HER proceeds via the Volmer‐Heyrovsky mechanism. The results obtained proved that the Pd/C electrode had a larger active surface area than the Ru/C one did.

The equilibrium constant ( K 1 (CrOH + )) of Cr 2+ hydrolysis was determined by the potentiometric method in trifluoromethanesulfonic solutions. Log K 1 is equal to −8.2 ±0.2, and the [OH − ]/[Cr(II)] ratio determined at the end of titration was equal to 2.00 ± 0.02. In chloride and perchlorate media the [OH]/[Cr(II)] ratio is much lower, indicating formation of mixed complexes. Chronocoulometric measurements in weakly acidic solutions of Cr 3+ showed that at pH 3.5–5, the Cr(OH) 2+ complex was reduced in a separate wave, which made possible determination of the first and the second hydrolysis constants of Cr 3+ . The derived p K values were 4.26 and 5.92, respectively. Analysis of the standard rate constant for the Cr(OH) 2+ /Cr(II), OH − redox couple proved that OH − ions have high catalytic influence on the Cr III/II system. The formal potential of the CR(III)X + e → Cr 2+ + X sytem is, in the presence of OH − , more negative than that for other ligands.

The parameters α, β and γ of the equation WΔsGf(MX) = αBKT + βET + γ were calculated and analysed for different salts (MX) in pure solvents and in non-aqueous solvent–water mixtures (S). Among 109 different equations, only 64 were taken for the final analysis since in the case of 38 equations the parameters BKT and ET were highly correlated. After a statistical analysis and normalization, on the basis of the coefficients α and β obtained, it was found that the ions analysed may be divided into three classes characterized by the different dependences of α on β: class I, H+, Li+, Na+, Rb +, Cs+, Me4N+, Cl−, Br− and I−, where αN = 1.074βN + 1.639; class II, Ag+, Cl−, Br−, I−, OAc−, SCN− and N where αN = 2.057βN + 2.147; and class III, Ph4As+, BPh, Ph4C and Ph4Ge, where αN is variable and βN is almost constant. Two main conclusions can be drawn out from the results obtained: the behaviour of ions considered as Lewis acids and bases reflects different hard–soft properties of the ions, and the behaviour of the Ph4As+ ion is different from that of BPh.

CrBr 2+ and CrI 2+ complexes formed during the electrooxidation of Cr 2+ on mercury electrodes in the presence of Br − and I − ions, respectively, aquate with rates ca. 10 3 higher than those measured by the spectrophotometric method in the bulk of the solution. The entropies of activation of these reactions are large and negative, which indicates that the transition states are highly organized. Changes in the H + concentration did not influence the rate of aquation. Since Cr 2+ ions are not oxidized on Pt, Au, glassy carbon or pyrolytic graphite electrodes, this high instability was explained in terms of the adsorption of the transition state on mercury during the inner-sphere electron transfer.

Supersaturated chromium amalgam as concentrated as 1.5 M, has been prepared electrochemically. The resulting amalgam has a mirror-like shine and behaves like plasticine. The stability of supersaturated (up to 10 mM) chromium amalgam was investigated in 1 and 5 M solutions of NaClO4, in the range of −20 to 60°C, using double potential step chronocoulometry (DPSC). The results enabled us to determine the conditions in which the oxidation of Cr(Hg) is diffusion controlled. In the millisecond time scale, this usually occurs at concentrations lower than 1 mM Cr3+ Cr(Hg) decomposes more rapidly at increased temperature and concentration of chromium in the amalgam, and, in the first stage, forms inactive clusters (probably Cr3). The energy of activation of this reaction was determined as Ea = 36.2 kJ mol .

A method for determining the oxygen content of the high-temperature superconductor YBa2Cu3O6.5+x is described. The superconductor is dissolved in 4.4 M hydrobromic acid, forming bromine. The mixture is then diluted with hydrochloric acid to obtain a solution of bromine and Cu(II) in 0.44 M hydrobromic acid and 1.1 M hydrochloric acid. As(III) is added in slight excess of that required to react with the bromine and the unreacted As(III) is determined by titration with potassium bromate. Oxygen does not interfere. The results of this method are in agreement with those of other iodimetric procedures. The dissolution of the superconductor in 4.4 M hydrobromic acid is much faster than in hydrochloric acid, the medium used in one iodimetric technique. YBa2Cu3O6.5+x sintered fibers and powder samples weighing from ca. 0.5 to 200 mg were analyzed for oxygen content.

The formal potentials and the kinetics parameters for the electrode process: Cr 2+ +2 e − = Cr o occurring at a mercury electrode in solutions of NaClO 4 , NaCI, NaBr, and NaSCN, were determined from the analysis of irreversible anodic and cathodic chronocoulometric waves. The interaction of Cr(II) with Cl − was found to be negligible (equilibrium constant K − and SCN − was weak ( K 1 (Br − )=1 M −1 and β 2 (SCN − ) = 25 M −2 ). The results of the analysis of the formal rate constant of this and other amalgam forming reactions suggested that the formation of amalgam was the most important step in the whole process.

Hydroxylamine oxidation in acidic media at the rotating platinum, gold, and glassy carbon electrodes was investigated. It was found that the reaction occurred only at the platinum electrode. A single oxidation peak (instead of a wave) was observed at the rotating platinum electrode. Evidence for a kinetic hindrance of the reaction caused by the platinum oxide layer present at the electrode surface was shown. The reaction proceeds via NHOH, NOH, nitrous acid, and the final products are nitrate ions. The process involves hydroxylamine adsorption, which is the reason for the absence of the electrochemical signal in the case of gold and carbon, materials of lower catalytic activity. Hydroxylamine oxidation was accompanied by various homogeneous chemical reactions. The reaction of hydroxylamine with nitrous acid (intermediate product of hydroxylamine oxidation), yielding N 2 O, had a rate constant, estimated on the basis of the ring-disk experiments, equal to (6.4 ± 0.4) 10 4 mol -1 cm 3 s -1 .

Electroreduction of chloramines (mono-, di-, and trichloramine) in I M NH 4 Cl solutions of different pH was investigated at the rotating platinum and gold electrodes. It was found that all chloramines are present in the solution in nonprotonated forms and give well-formed one-step or two-step current-potential waves. The final products of reduction are ammonium (or ammonia) and chloride ions. Monochloramine is reduced in a single two-electron irreversible wave. Hydrazine is not an intermediate in monochloramine reduction. Dichloramine reduction generally proceeds in two two-electron steps (via monochloramine). Below pH 4.3 a kinetic current due to the protonated dichloramine reduction (single four-electron wave) is in force, appearing as an increase of the height of the first step on lowering pH. Due to this process below pH 2.5 only one four-electron reduction wave is observed. Trichloramine reduction occurs in two steps: two-electron trichloramine to dichloramine reduction and four-electron dichloramine reduction. In strong acidic solutions the kinetic current due to the protonated trichloramine reduction has to be taken into account. A reaction mechanism common for all chloramines was proposed with [NXCl.] as an intermediate (X = H 2 , HCl, and Cl 2 for mono-, di-, and trichloramine, respectively). The rate-determining step does not involve proton transfer.

The nitrite oxidation process was reinvestigated at rotating gold and platinum electrodes covered by an oxide layer. The electrochemical properties of the surface oxides were determined by recording the coverage curves of the gold and platinum electrodes at various pH values and for different experiment durations. The reaction mechanism on the oxidized surface was found to be the same as that on the oxide-free surface. The sole effect of the surface oxide was a drop of the standard rate constant of the electrode reaction which was a function of the surface coverage by the oxide. Nitrite oxidation on the oxide-covered electrodes was found to proceed via the innersphere mechanism with inhibitor adsorption on an energetically uniform surface. The kinetic results obtained for the gold and the platinum electrode were almost the same. The complicated shape of rotating disk voltammograms was explained in terms of the increase of the rate of the electrode reaction with increasing electrode potential and the drop of the standard rate constant of the electrode reaction with increasing electrode potential due to the increase of the oxide coverage with electrode potential, the latter process being dependent on the electrode material, pH, and time (scan rate).

High affinity of thallium(I) ions with respect to a copper hexacyanoferrate (CuHCF) film was found. Interaction between the CuHCF film and thallium(I) ions was investigated using the electrochemical quartz crystal microbalance and cyclic voltammetric techniques. In 0.5 M KNO 3 solution, at submillimolar concentrations of Tl(I) ions, the CuHCF film reversibly transforms, during electrochemical experiments, from the potassium into the thallium form. For slightly higher (several millimoles) Tl(I) concentrations, the electrochemical and gravimetric responses prove that the CuHCF film behaves as the thallium form only. Its formal potential (E f 0 ), calculated from the dependence of the E f 0 on [Tl(I)], is for [Tl(I)] = 1 M, 0.28 V more positive than that found for the potassium form. Experimental results obtained suggest that in both cases, potassium(I) and thallium(I) ions, exchange in interstitial positions takes place. Since the ionic radii and the hydration parameters of both ions are similar, we concluded that this high affinity of thallium(I) ions with respect to the CuHCF film, 250-100 times higher than that of potassium(I) ion, results from chemical interactions. In consequence, the solubility product of a thallium analogue of copper hexacyanoferrate is much smaller than that of the potassium form. For different forms they are equal to (pK values): 37.8 (K 2 Cu 3 [Fe(CN) 6 ] 2 ), 46.3 (Tl 2 Cu 3 [Fe(CN) 6 ] 2 ), and 17.2 (Cu 3 [Fe(CN) 6 ] 2 ).

Donnees sur le processus d'electrode Cr(II)+2e − =Cr(O) en presence d'une electrode de mercure, souvent observe comme 2eme etape de la reduction d'ions Cr(III), entre pH 2 et 4

The influence of the ionic strength, pH, nature of the background electrolyte and its concentration as well as the influence of the electrode material (Pt, glassy carbon, carbon paste) on the electrode kinetics of the MnO−4/MnO−24 and MnO2−4/MnO3−4 systems has been investigated by means of cyclic voltammetry and the rotating disc electrode method. Rate constants determined with the use of the carbon paste electrode agreed well with those which were in some instances available in the literature. At the Pt. electrodes the rate could be only estimated. The rate constants obtained for both electrode reactions were considered in terms of the Marcus theory. Also the charge of rate constants and formal potentials with studied parameters was discussed.

It has been found that Snyder's eluant strength parameter e°, used in liquid-solid adsorption chromatography, can be well described by a complementary Lewis acid-base model for solute-solvent interactions: e°=0.152+0.859 · E N T + 0.332 · B KT ( cf Eq.9 ), with a correlation coefficient of r = 0.949 for 28 solvents. This result is in agreement with the theoretical interpretation of e° The correct statistical procedure for estimating the significance of added explanatory parameters in the sequential multiparameter regression analysis is shown ( cf Appendix). A comprehensive list of improved Kamlet-Taft solvent basicity parameters, B KT , is given.

Oxidation of Cr2+ at mercury electrodes in the presence of S2O2−3, thiosemicarbazide, 2,5-dimercapto-1, 3,4-thiadiazole, N-methylthiourea, thiourea and thioacetamide lead to Cr(III) complexes which feature a chromium(III)-sulphur bond. The equilibrium constants of these complexes are equal to 0.21, 0.14, 0.036, 0.0076, 0.0013 and 0.00015 M−1 for S2O2−3, TSC, DMTDA, NMTU, TU and TAA, respectively. The Cr(III)TU complex synthesized electrochemically aquates spontaneously, and the mechanism of this reaction is the same as that characteristic of other Cr(III)X(3-i)+ complexes. This complex is not adsorbed on the electrode surface.

Assuming a straight-line dependence of the chemical potential of anions (cations) on empirical Lewis acid (base) parameters of solvents, the values of the change of the chemical potential of ions and the change of the surface potential between water and non-aqueous solvents have been calculated and briefly discussed. On the basis of the results obtained and literature data the dependence of the standard emf of the cell Pt,H2 |HCl|AgCl|Ag|Pt′ on the function of empirical Lewis acid-base parameters has been analysed and discussed.

The Kamlet and Taft basicity parameters βKT, for twelve mixtures of organic solvents with water are reported. Also the data for water-butanols (n-BuOH. i-BuOH. and s-BuOH) and alcohols (MeOH, EtOH. n-PrOH. and i-PrOH)-n-hexane mixtures are given. It was found that in the case of mixtures of 1.4-dioxane. acetone, tetrahydrofuran. dimethylsulfoxide. and acetonitrile with water, the basicity parameters of the mixture are higher than that of pure solvents in a region of smaller concentrations of water. These results, together with earlier reported results for THF and Et2O mixtures with MeOH are discussed in terms of breaking off the structure of the more structurized solvent (water and MeOH). All these mixtures, except the W-THF mixture, show the excess thermodynamic func­tions (ΔHE and ΔSh) analogous to MeOH-CCl4 mixtures, where depolymerization of MeOH clusters was postulated. Relativity of different basicity scales in respect to the acidic probe molecule is also shortly discussed

Empirical parameters of Lewis acidity, E N T , introduced by Reichardt et al., and Lewis basicity, B KT , introduced by Kamlet and Taft, have been determined for mixtures of water with ten organic solvents. In the case of water/alcohol mixtures a distinct dependence between these acidity and basicity parameters have been found. For the other solvent mixtures the E N T on B KT dependence is more complex even if these parameters are purified from non-specific solute/solvent interactions.

The electrode process Bi(III)+ 3e = Bi(Hg) has been investigated in weakly acidic, neutral and alkaline solutions by means of amalgam polarography and cyclic voltammetry and chronopotentiometry with the use of hanging amalgam drop electrode. It has been found that in weakly acidic and neutral solutions, oxidation of bismuth amalgam goes through aquocomplexes of bismuth. In the cathodic step on cyclic voltammetry curves four peaks of reduction are observed, with magnitude and shape strongly dependent on pH of the solution. These peaks have been ascribed to the reduction of Bi3+, Bi(OH)+2, Bi(OH)+2 and Bi(OH)3. In alkaline solutions, oxidation of bismuth amalgam leads to Bi(OH)3. In cathodic scan on cyclic voltammetry curves only one peak is observed, which corresponds to Bi(OH)3 reduction. Formal potentials of electrode process and solubility product of Bi(OH)3 have been calculated and discussed. The step-wise nature of the overall electrode reaction has been ascertained and discussed. At higher concentrations of OH− ions, Bi(OH)3 dissolves.

A critical analysis is given of currently popular scales of solvent Lewis basicity (Koppel–Palm, Paju–Koppel, and Gutmann) with particular consideration to and extension of the Kamlet–Taft scale, BKT. Measurements for 22 new solvents were carried out and BKT values for 70 solvents are reported. A rough agreement between BKT and other parameters for solvent basicity has been found. A linear dependence of the Koppel–Palm E values with ET was shown for solvents of higher polarity (ET > 42).

The electrode process Bi(III)+ 3e = Bi(Hg) has been investigated in weakly acidic, neutral and alkaline solutions by means of amalgam polarography and cyclic voltammetry and chronopotentiometry with the use of hanging amalgam drop electrode. It has been found that in weakly acidic and neutral solutions, oxidation of bismuth amalgam goes through aquocomplexes of bismuth. In the cathodic step on cyclic voltammetry curves four peaks of reduction are observed, with magnitude and shape strongly dependent on pH of the solution. These peaks have been ascribed to the reduction of Bi3+, Bi(OH)+2, Bi(OH)+2 and Bi(OH)3. In alkaline solutions, oxidation of bismuth amalgam leads to Bi(OH)3. In cathodic scan on cyclic voltammetry curves only one peak is observed, which corresponds to Bi(OH)3 reduction. Formal potentials of electrode process and solubility product of Bi(OH)3 have been calculated and discussed. The step-wise nature of the overall electrode reaction has been ascertained and discussed. At higher concentrations of OH− ions, Bi(OH)3 dissolves.

Kinetics of the hydrogen evolution reaction (her) were measured at a rhodium electrode in a 1 M solution of KOH at various temperatures between 5 and 75°C. The measurements were conducted at a Rh wire electrode activated before every measurement by cycling in the range of potentials between −1.0 and 0.3 V (vs. Hg/HgO/1 M KOH) until a stationary behaviour was obtained. Experiments were also carried out on the electrode kept at 25°C for three days at −1.0 V. In this case the current was by about one order of magnitude lower than that observed for the activated electrode. For both electrodes the her could be described by the Volmer-Heyrovsky mechanism. For activated electrodes the cathodic transfer coefficient α changed with temperature from 0.3 to 0.4; at deactivated electrode it was equal to 0.43. The activation resistance decreased with temperature by almost two orders of magnitude. The results were analysed according to two models of the impedance on solid electrodes. An approximation of both the Tafel plots and the logarithm of the reaction admittance vs. overpotential made the calculation of the rate constant of the slowest step possible, which was three orders of magnitudes greater than that for the nickel electrode. Total capacities of the double layer at poisoned and activated electrodes were almost the same and equal to 60–80 μF cm−2. We have concluded that traces of metallic impurities are responsible for poisoning of the electrode.

The use of the stable 2,2,6,6-tetramethylpiperidine N-oxyl (TMPNO) radical as a standard base made it possible to introduce a new scale of Lewis acidity for solvents. The parameter EB is defined as the energy (in kJ mol–1) of n–π* transition in the TMPNO spectrum measured in different solvents; it correlates very well with other scales of Lewis acidity such as ET, AN, and Z. Interaction of TMPNO with inorganic acids (H+ and Li+) in water is different as evidenced by changes in the absorption spectra.