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Electric double layer structure and adsorption of cyclohexanol on single crystal cadmium, antimony and bismuth electrodes

The electric double layer structure in aqueous and non-aqueous surface inactive electrolyte solutions and the adsorption of cyclohexanol on the electrochemically polished Sb, Bi and Cd electrodes were studied by using cyclic voltammetry, impedance and chronocoulometry. The limits of ideal polarizability, the potentials of zero charge and the values of capacity of inner layer were established. As found, the differences between the zero charge potential for various planes depend on the chemical nature and crystallographic structure of the electrode surface, as well as on the chemical nature of the solvent studied. The inner layer capacity at negative surface charges depends on the crystallographic orientation of the single crystal planes and on the electronic properties of the electrode metal. The inner layer capacity increases in the sequence of metals Sb < Bi < Hg < Cd < Zn, as the hydrophility of electrodes increases and as the contribution of metal phase decreases. The values of capacity of metal phase and the effective thickness of the thin metal surface layer were calculated by using various theoretical approximations. The effective thickness of the thin layer of metal surface increases in the sequence of metals Ga < Zn < Cd < Hg < Bi < Sb as the metallic properties of electrodes decrease. The adsorption parameters of cyclohexanol were established by using Frumkin-Damaskin adsorption theory. It was found that the adsorption characteristics depend on the chemical nature and crystallographic structure of electrode surface. The adsorption activity of cyclohexanol increases in sequence of metals Zn < Cd < Bi < Hg < Sb as the adsorption energy of solvent decreases.

Adsorption of halide anions on bismuth single crystal plane electrodes

Adsorption behaviour of Cl - , Br - and I anions on Bi single crystal plane electrodes from aqueous, methanol and 2-propanol solutions has been studied by impedance spectroscopy and chronocoulometry methods. The values of surface excess and the Gibbs energy of adsorption of halide ions on the Bi(111), Bi(001) and Bi(011) single crystal planes have been calculated using the electrode potential E and the surface charge density a as the independent electrical variables. It was found that under comparable conditions the result obtained at constant E and at constant a are coincident. The formal charge transfer coefficient (so called electrosorption valency) and the dipole moment of the dipole formed by an adsorbed halide ion and its image charge in Bi plane have been calculated. It was found that on the Bi(111) plane, where the chemical bonds are all saturated, the formal charge transfer coefficient and the dipole moment of adsorbed anion are independent of electrode potential. For more active Bi planes there is noticeable dependence of both characteristics on electrode charge and at higher positive charges the covalent bonding between Bi(011) surface atoms and I - is probable. It was concluded that the dipole formed is significantly screened by the solvent molecules and the metal electron gas, but the influence of the solvent dielectrical and other characteristics on the effective dipole moment values is comparatively small.

Adsorption of Cl− and Br− ions on the (001) plane of a bismuth single crystal from solutions in 2-propanol

Abstract The adsorption of Cl − and Br − ions on the (001) plane of a bismuth single crystal electrode from solutions in 2-propanol has been investigated using differential capacity measurements. The ionic charge due to the specific adsorption has been calculated by the Hurwitz-Parsons-Dutkiewicz method. The results have been analysed on the basis of the virial adsorption isotherm. It has been found that the adsorption parameters for the (001) plane and the polycrystalline electrode do not differ significantly.

Adsorption of iodide ions on bismuth single crystal planes from solutions in ethanol

The adsorption of I− ions on the singular (111), (001) and (011) planes of the bismuth single crystal from solutions in ethanol has been investigated by electrode impedance and charge measurement methods. The ionic charge due to the specific adsorption was obtained using the mixed-electrolyte method for both electrode charge and electrode potential as independent electrical variables. The Gibbs energy of adsorption of I− ions was calculated using the simple virial adsorption isotherm. It was found that under comparable conditions the results obtained at constant electrode potential and at constant electrode charge are coincident and the adsorption of I− anion increases in the sequence of Bi single crystal planes (111)<(001)<(011) and solvents methanol<ethanol. The electrosorption valency and the effective dipole moment of the dipole formed by an adsorbed halide ion and its image charge in the Bi plane have been calculated. It was found that on the Bi(111) plane, where the chemical bonds are all saturated, the electrosorption valency has a constant value in the potential range studied while on the more active Bi planes it depends on the electrode potential. It was concluded that the effective surface dipole formed is screened by the solvent molecules and the metal electron gas significantly. The surface dipole value diminishes on moving from Bi(111) plane to more active planes.

An impedance and chronocoulometric study of the adsorption of chloride and bromide ions on bismuth single crystal planes from solutions in methanol

The adsorption of Cl− and Br− ions on the (111), (001) and (011) planes of a bismuth single crystal electrode from solutions in methanol has been investigated by means of differential capacity and coulometric measurements. The ionic charge due to the specific adsorption has been obtained using the mixed-electrolyte method. The results have been analysed and some characteristics calculated by the simple virial adsorption isotherm and classical inner layer model. It has been found that the difference in the adsorption characteristics for various planes of the Bi single crystal is rather small in methanol and it depends on solvent nature in a quite complicated manner. The analogous difference in inner layer capacity in methanol has been found to be close to that difference in ethanol and water, but much lower than in 2-propanol.

Calculation of thermodynamic and inner layer characteristics of halide ions adsorbed on bismuth single crystal planes from solutions in methanol

Abstract The values of the surface excess and the Gibbs energy of adsorption of halide ions on the (111), (001) and ( 01 1 ) Bi single crystal planes in methanolic solutions have been calculated from the previously obtained experimental data using electrode potential as the independent electrical variable. It was found that under comparable conditions the results obtained at constant electrode potential and at constant electrode charge are coincident. The electrosorption valency and the dipole moment of the dipole formed by an adsorbed halide ion and its image charge in the Bi plane have been calculated. It was found that on the Bi(111) plane, where the chemical bonds are all saturated, the electrosorption valency does not depend on electrode charge and in the measured range of potentials a weak dependence of the dipole value formed by an adsorbed halide ion and its image charge in Bi on the electrode charge was found. In contrast, on the more active Bi planes there is noticeable dependence of both characteristics on electrode charge and at higher positive charges, covalent bonding between Bi( 01 1 ) surface atoms and I − anions is probable. It was concluded that the dipole formed is screened significantly by the solvent molecules and the metal electron gas.

Calculation of the characteristics of Cl- and Br-ions adsorption on bismuth single-crystal planes from solutions in 2-propanol

Abstract The values of the surface excess and the Gibbs energy of adsorption of halide ions on the (111) and (001) Bi single-crystal planes in solutions in 2-propanol have been calculated from the previously obtained experimental data using electrode potential as the independent electrical variable. It was found that under comparable conditions the results obtained at constant electrode potential and at constant electrode charge are coincident. The electrosorption valency and the dipole moment of the dipole formed by an adsorbed halide ion and its charge image in the Bi plane have been calculated. It was found that on the Bi(111) plane, where the chemical bonds are all saturated, the electrosorption valency does not depend on the electrode charge. In contrast, on the more active Bi(001) plane there is a noticeable dependence of the electrosorption valency on the electrode charge. The dipole value formed by an adsorbed halide ion and its charge image in Bi significantly diminishes when changing from negative to positive electrode charge density and at the higher positive charges the covalent bonding between the Bi(001) surface atoms and Br− anions is probable. The more complicated dependence of the dipole value on electrode charge at the Bi(111) planes was attributed to the change in solvent structure on the electrode surface. It was concluded that the dipole formed is significantly screened by the solvent molecules and the metal electron gas.

Adsorption of bromide ions on bismuth single crystal planes from solutions in ethanol

The adsorption of Br - ions on the (111), (001) and (011) planes of the bismuth single crystal from solutions in ethanol has been investigated by differential capacity and electrode charge measurement methods. The ionic charge due to the specific adsorption has been obtained using the mixed-electrolyte method for both electrode charge and electrode potential as the independent electrical variables. The Gibbs energy of adsorption of halide ions has been calculated using the simple virial adsorption isotherm. It was found that under comparable conditions the results obtained at constant electrode potential and at constant electrode charge are coincident and the adsorption of Br anions increases in the sequence of Bi single crystal planes (111) < (001) < (011) and solvents methanol < ethanol < 2-propanol. The electrosorption valency and the dipole moment of the dipole formed by an adsorbed halide ion and its image charge in the Bi plane have been calculated. It was found that on the Bi(111) plane, where the chemical bonds are all saturated, the electrosorption valency has a constant value, while on the more active planes it depends on electrode charge. It was concluded that the surface dipole formed is screened significantly by the solvent molecules and the metal electron gas. The surface dipole value diminishes when changing from negative to positive electrode charge and from the (111) plane to more active planes. The complicated dependence of the dipole value on the electrode charge at the Bi(111) plane was attributed to the change in solvent structure on the electrode surface.

Adsorption of inorganic ions on bismuth from constant ionic strength solutions in 2-butanol

Abstract The adsorption of Cl − , Br − , I − and SCN − ions on a drop-shaped bismuth electrode from solutions in 2-butanol has been investigated by means of differential capacity measurements. The ionic charge due to the specific adsorption was calculated using the Hurwitz-Parsons-Dutkiewicz method. The results were analysed using the virial adsorption isotherm and the classical Grahame-Parsons inner layer model. It was confirmed that the standard Gibbs energy of adsorption of ions in alcohols can be correlated with quantum-chemical indices of reactivity.

Electrical double layer and adsorption of iodide ions at the Bi | acetonitrile interface

The adsorption of I− ions on the Bi(111) single crystal plane from solutions in acetonitrile has been investigated by impedance measurement method. The ionic charge due to the specific adsorption has been obtained using the mixed electrolyte method applied for both electrode charge and electrode potential as the independent electrical variables. The Gibbs energy of ions adsorption has been calculated using the virial adsorption isotherm. It was found that under comparable conditions the results obtained at constant electrode potential and at constant electrode charge are coincident and the Gibbs energy of I− anion adsorption increases in the sequence of solvents: methanol < ethanol < propylene carbonate < acetonitrile. The electrosorption valency has been calculated and it was found that this parameter increases in the sequence propylene carbonate < ethanol < methanol < acetonitrile.