Bi Single Crystal Planes Research Articles

Electrochemical Characterisation of Adsorption of Halide Ions at Bi(111) Electrode from Ionic Liquids and Their Mixtures

In recent years, application of ionic liquids as electrolytes in electrochemical devises has become more and more routine. Indeed, non-aqueous electrolytes can provide higher cell potential without decomposing. For electrochemical double layer capacitors (EDLCs) the widening of the cell potential increases exponentially the energy and power densities. There are several studies analyzing the strong adsorption of halide ions at Bi single crystal planes from classical electrolyte solutions demonstrating a maximum in C, E -curves in the presence of specifically adsorbed I−, Br− or Cl− anions. [1–4] Our recent studies have shown that the addition of specifically adsorbed iodide ions strongly influences the electrochemical characteristics of RTILs systems increasing the specific capacitance and decreasing the series resistance values [1]. The main aim of this study was to investigate the adsorption of Br− ions and electrochemical double layer parameters in ionic liquid media. The cyclic voltammetry and electrochemical impedance spectroscopy methods have been applied to investigate the electrical double layer formation and adsorption kinetic parameters of Br− anions at the electrochemically polished Bi(111) electrode surface. 1-ethyl-3-methylimidazolium bromide, 1-ethyl-3-methylimidazolium tetrafluoroborate were used to prepare the mixture of ionic liquids in order to increase the differential capacitance of the system, decrease the viscosity and lower the price of the ionic liquids mixture [5]. Furthermore, EMIm + halides have shown very good thermal stability, i.e. they are suitable electrolytes for higher temperatures as well. The measured ideal polarizability region from – 1 to 0 V is in a good agreement with impedance data. The mixed kinetic processes take place on both systems (Bi(111)|EMImBF4 + EMImI and Bi(111)|EMImBF4 + EMImBr). The series differential capacitance (C s) values have been calculated from Nyquist dependencies at different fixed ac frequencies from 0.2 to 10000 Hz (C s = (Z''i2πf)−1; where i = √−1). C s depends on the electrode potential and ac frequency being somewhat higher for lower frequencies. The maximum capacitance values are aproximatley 15% lower than those for EMImBF4 + EMImI system. Acknowledgments: This study was partially funded by the Estonian Energy Technology Program project SLOKT10209T, Estonian Basic Research project SF0180002s08, PUT55, IUT20-13 and Estonian Centers of Excellence in Science project: High-technology Materials for Sustainable Development TK117 References [1] C. Siimenson, L. Siinor, K. Lust, E. Lust, J. Electroanal. Chem. 730 (2014) 59. [2] L. Siinor, V. Ivaništšev, K. Lust, E. Lust, J. Solid State Electrochem. 14 (2010) 555. [3] K. Lust, M. Väärtnõu, E. Lust, Electrochimica Acta 45 (2000) 3543. [4] T. Thomberg, T. Tooming, K. Tõnurist, L. Siinor, A. Jänes, E. Lust, in:, Meet. Abstr., The Electrochemical Society, 2014, pp. 173–173. [5] A. Efimova, L. Pfützner, P. Schmidt, Thermochim. Acta 604 (2015) 129.

Adsorption of iodide ions on the Cd(0001) single crystal plane in methanol

The adsorption of I− ions on the Cd(0001) single crystal plane from solutions in methanol has been investigated by impedance measurement method. 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 ions has been calculated using the different modifications of 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 adsorption of I− anion increases in the sequence of solvents: water < methanol, ethanol, and metals: Cd < Bi. The electrosorption valency has been calculated. It was found that on the Cd(0001) plane the electrosorption valency of I− anions has a constant value that is similar for methanol and ethanol and also for these solvents on Bi single crystal planes.

Study of adsorption of tetraethylammonium ions on Bi single crystal planes from solutions in ethanol

The adsorption of tetraethylammonium (TEA+) ions on the (001) and \( {\left( {01\overline{1} } \right)} \) planes of the bismuth single crystal from solutions in ethanol has been investigated by impedance measurement method. The experimental data were obtained in 0.02 M mixed-electrolyte solutions and the calculations performed with electrode potential as the independent electrical variable. The Gibbs energy of adsorption of TEA+ ions has been calculated using the simple virial adsorption isotherm, and it was found that the adsorption of TEA+ cations is weaker than the adsorption of halide anions. The electrosorption valency evaluated has a nearly constant value in the potential region studied. It was concluded that the formed effective surface dipole is significantly screened by the solvent molecules and the metal electron gas. The analysis of the impedance spectra was performed by fitting the experimental data to the various equivalent circuits. It was found that the behaviour of TEA+ ions at Bi(hkl)∣ethanol interface can be described with the equivalent circuit, corresponding to the classical Frumkin–Melik-Gaikazyan model. The results obtained indicate that only weak interaction between TEA+ ions and bismuth surface takes place, and there is no remarkable partial charge transfer from the adsorbed ions to the Bi surface atoms.

Impedance study of chloride ions adsorption on Bi(1 1 1) and [formula omitted] single crystal planes in ethanol

The impedance spectra for Bi(111) and Bi ( 01 1 ¯ ) single crystal planes in 0.1, 0.02 and 0.005 M LiCl solutions in ethanol have been measured in the range of ac frequencies between 0.1 and 10 000 Hz and electrode potentials −1.4 < E < −0.2 V (vs. aqueous saturated calomel electrode). By fitting of the experimental data to various equivalent circuits, it was found that the Frumkin–Melik-Gaikazyan model yields to the good fit in almost the whole potential range studied. Using this model, the dependencies of “true” and adsorption capacitance on electrode potential have been calculated. The ionic charge due to the specific adsorption of Cl − ions has been obtained using the mixed-electrolyte method in 0.1 M solutions for both electrode charge and electrode potential as the independent electrical variables. The Gibbs energy of adsorption of Cl − ions has been calculated using the simple virial adsorption isotherm. It was found that the adsorption of Cl − anion increases in the sequence of Bi single crystal planes ( 1 1 1 ) < ( 0 0 1 ) ⩽ ( 0 1 1 ¯ ) and solvents methanol < ethanol < 2-propanol. It was found that the electrosorption valency has a constant value in the potential range studied. It was concluded that the formed effective surface dipole is significantly screened by the solvent molecules and the metal electron gas.

Impedance characteristics of iodide ions adsorption on Bi single crystal planes in ethanol

The impedance spectra for Bi(1 1 1), Bi(0 0 1) and Bi (0 1 1 ̄ ) single crystal planes in 0.1 M LiI solution in ethanol have been measured. It was found that reproducible experimental data for Bi electrodes in ethanol solutions could be obtained in the range of ac frequencies between 0.1 and 10,000 Hz and electrode potentials −1.6< E<−0.2 V (vs. aqueous SCE). Outside this potential region the occurrence of faradaic processes was detected. By fitting the experimental data to various equivalent circuits it was found that the Frumkin–Melik-Gaikazyan model yields a good fit at E<−0.6 V, but at E⩾−0.6 V, more complex equivalent circuits should be introduced. Using these models the dependences of “true” and adsorption capacitances as well as diffusion resistance on electrode potential have been obtained. It was proposed that, at E>−0.6 V for all Bi single crystal planes studied, the formation of a surface compound is probable.

Adsorption of 1-heptanol on bismuth single-crystal plane electrodes

Cyclic voltammetry, impedance and chronocoulometry have been employed for the quantitative study of 1-heptanol (1-HepOH) adsorption on the bismuth single-crystal plane|aqueous Na2SO4 solution interface. The adsorption isotherms, Gibbs energies of adsorption, $$ \Delta G_{\rm A}^ {\circ} $$ , the limiting surface excess, Γmax, and other adsorption parameters have been determined. The adsorption of 1-HepOH on Bi single-crystal planes is mainly physical and is limited by the rate of diffusion of organic molecules to the electrode surface. Comparison of the adsorption data for 1-HepOH with other alcohols shows that the adsorption characteristics depend on the structure of the hydrocarbon chain. The adsorption activity of adsorbates at the bismuth|solution interface increases in the sequence 1-propanol<1-butanol<1-pentanol<1-hexanol<1-heptanol as the adsorption activity at the air|solution interface increases. For all the compounds studied, the adsorption activity increases in the sequence of planes as $$ (111) < (001) < (01\overline 1 ) $$ .

Analysis of impedance spectra of the Bi single crystal planes in solutions of LiClO 4 in ethanol

The impedance spectra for Bi(111), Bi(001) and Bi(01 1 ̄ ) single crystal planes in 0.1 M LiClO 4 solution in ethanol have been measured. It was found that reproducible experimental data for these electrodes in ethanol solutions could be obtained in the range of ac frequencies between 0.1 and 10 000 Hz. The measurements indicated that the Bi single crystal planes in 0.1 M LiClO 4 solution in ethanol could be regarded as an ideally polarisable electrode in the region of potentials −1.6< E<−0.05 V (vs. aqueous SCE). Outside of this potential region the occurrence of Faradaic processes was detected. By fitting the experimental data to various equivalent circuits (EC) it was found that the Frumkin–Melik-Gaikazyan model yielded the best fit. Using this model the dependencies of ‘true’ and adsorption capacitance and diffusion resistance on electrode potential have been obtained. The values of parameters revealed no significant differences between various Bi planes. It was proposed that the dependence of these parameters on electrode potential was mainly determined by the different sizes of ions and polarisation of solvent molecules. The parameters also indicate the weak adsorption of ClO 4 − ions at positive electrode potentials.

Adsorption of anions on bismuth single crystal plane electrodes from various solvents

The adsorption behaviour of Cl −, Br − and I − anions on Bi single crystal plane electrodes from aqueous, methanol, ethanol, 2-propanol and acetonitrile solutions has been studied by impedance spectroscopy and chronocoulometry methods. The values of the surface excess and Gibbs energy of adsorption of halide ions on the Bi(111), Bi(001) and Bi( 01 1 ̄ ) single crystal planes have been calculated, using the electrode potential E and the surface charge density σ as the independent electrical variables. Analysis of data shows that, under comparable conditions, the results obtained at constants E and σ are coincident. The formal charge transfer coefficient (so-called electrosorption valency) and the dipole moment of the dipole, formed by a halide ion adsorbed and its image charge in the Bi plane, have been calculated. For the Bi(111) plane, where the chemical bonds are all saturated, the formal charge transfer coefficient and the dipole moment of adsorbed anion are practically independent of electrode potential. For more active Bi planes, there is noticeable dependence of both characteristics on the electrode charge, and at higher positive charges, the covalent bonding between Bi( 01 1 ̄ ) surface atoms and I − is probable. Comparison of these data with those for vacuum ∣ metal interfaces shows that the dipole formed is significantly screened by the solvent molecules as well as by the metal electron gas, but the influence of the dielectric and other characteristics of solvent on the values of the effective dipole moment is comparatively small.

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

The adsorption of I − ions on the singular (111), (001) and (011̄) 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)<(011̄) 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.

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 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( 01 1 ̄ ) single crystal planes have been calculated using the electrode potential E and the surface charge density σ as the independent electrical variables. It was found that under comparable conditions the result obtained at constant E and at constant σ 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( 01 1 ̄ ) 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.

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

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.

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

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.

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

The adsorption of I − ions on the (111), (001) and (011̄) planes of a bismuth single crystal electrode from solutions in methanol has been investigated by means of differential capacity and electrode charge measurements. The ionic charge due to the specific adsorption has been obtained using the mixed-electrolyte method. The results have been analyzed 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 of I − ions on various planes of the Bi single crystal in methanol is more pronounced than in the case of Cl − and Br − ions. This is caused by the much stronger adsorption of I − ions on Bi that reduce the influence of the solvent on the adsorption process. The difference in inner layer capacity for various Bi single crystal planes in methanol has been found to be lower than that in 2-propanol and close to that in ethanol and water.

Adsorption of propanol on bismuth single-crystal-plane electrodes

Cyclic voltammetry, impedance and chronocoulometry have been employed for the quantitative study of 1-pentanol (n-PenOH) adsorption at the bismuth single-crystal plane | aqueous Na2SO4 solution interface. The adsorption isotherms, Gibbs energies of adsorption ΔGA∘, the limiting surface excess Γmax and other adsorption parameters, dependent on the crystallographic structure of the electrodes, have been determined. The adsorption of n-PenOH on Bi single-crystal planes is mainly physical and is limited by the rate of diffusion of organic molecules to the electrode surface. Comparison of the adsorption data for n-PenOH with 1-propanol (n-PrOH), 1-butanol (n-BuOH), cyclohexanol (CH) and 1-hexanol (n-HexOH) shows that the adsorption characteristics depend on the structure of the hydrocarbon group. The adsorption activity of adsorbates at the bismuth | solution interface increases in the sequence n-PrOH < n-BuOH < CH ≤ n-PenOH < n-HA as the adsorption activity at the air | solution interface increases. For all the compounds studied, the adsorption activity increases in the sequence of planes (111)<(001)<(011¯).

Adsorption of isomers of butanol on bismuth single crystal plane electrodes

Cyclic voltammetry, impedance and chronocoulometry have been employed for quantitative study of normal butanol ( n-BA), iso-butanol ( iso-BA), sec-butanol ( sec-BA) and tert-butanol ( tert-BA) adsorption at the bismuth single crystal plane¦aqueous Na 2SO 4 solution interface. The adsorption isotherms, Gibbs energies of adsorption, the surface excess and other adsorption parameters have been determined. As found, the adsorption characteristics of the isomers of butanol depend on the crystallographic structure of the electrodes, as well as on the geometrical structure of hydrocarbon chains of adsorbate. The adsorption characteristics obtained from the impedance and chronocoulometric measurements are in good agreement within the limits of surface charge densities — 24 < σ < 3 μC cm −2. The adsorption of n-BA, sec-BA, iso-BA and tert-BA on Bi single crystal planes is physical and is limited by the rate of diffusion of organic molecules to the electrode surface. The adsorption activity of adsorbates at the bismuth¦solution interface increases in the sequence tert-BA < sec-BA < iso-BA < n-BA as the adsorption at the air¦solution interface increases. In the case of all compounds studied, the adsorption activity of planes increases in the sequence (̄10̄1) ≤ (001) < (2̄1̄1) < (01̄1) as the superficial density of atoms increases. According to the values of the standard Gibbs energy of adsorption, it was established that the hydrophilicity of electrodes increases in the sequence Sb(111) < Bi(01̄1) < Bi(211¯) < Bi(̄10̄1) ≤ Hg < Bi(001) < Bi(111) < Cd(0001) < Zn(0001) < Ag(111) < Ag(100) < Ga.