Base Electrolyte Concentration Research Articles

Boosting the visible-light-driven photocatalytic efficiency in porous Cu/TiO2 ceramic coatings

In this study, we examined how current density, sodium phosphate concentration, and the addition of copper sulfate to the supporting electrolyte affect PEO coatings on pure titanium. The chemical composition, morphology, and optical behavior of PEO coatings were extensively analyzed using scanning electron microscopy (SEM), X-ray diffraction (XRD), and UV–Vis diffuse reflectance spectroscopy (DRS). With an increase in current density from 6 to 18 A/dm2, the coating's pore size enlarges and the rutile phase content within the coatings increases. The coating created at 12 A/dm2 shows the highest photocatalytic activity and triggers a unique three-stage behavior in the voltage-time diagram. Adding 4 g/l of CuSO4 to the electrolyte resulted in the formation of an unwanted Cu-based precipitates, causing electrolyte instability. To stabilize it, potassium hydroxide was removed, and the base electrolyte concentration was adjusted. To address this issue, potassium hydroxide was eliminated from the supporting electrolyte. Subsequently, the concentration of the base electrolyte was optimized. Also, the synergistic influence of CuSO4 addition (4 g/l) to the supporting electrolyte at different concentrations of 5, 10, and, 15 g/l of trisodium phosphate on PA was investigated. The superior photocatalytic performance of the optimum coating created in the electrolyte containing 5 g/l trisodium phosphate and 4 g/l CuSO4 is attributed to its enhanced porous structure, along with the heterojunction between the anatase and rutile phases. These features significantly boost the available surface area and facilitate the efficient separation and transfer of photogenerated charge carriers. Ultimately, a mechanism for MB photodegradation was proposed based on the findings from Mott-Schottky analysis and DRS.

The kinetics of electroreduction of europium(III) cations at bismuth single-crystal electrode

Electroreduction of Eu(ClO4)3 and Eu2(SO4)3 has been studied at electrochemically polished \( {\text{Bi}}\left( {01\bar{1}} \right) \) single-crystal electrode in an acidic HClO4 or H2SO4 (pH ~3) aqueous solution with LiClO4 or Na2SO4 additions as a surface inactive electrolyte. The Eu3+ cations electroreduction rate depends on the electrode potential applied and the concentration of the supporting electrolyte as well as the concentration of the Eu3+ ions. At the more negative electrode potentials than the zero charge potential (zcp), the diffusion current plateaus were observed. The values of the rate constant for the heterogeneous reaction calculated at zcp are independent of the base electrolyte concentration studied. Analysis of the kinetic data corrected for the electrical double-layer effect shows that the coincidence of the corrected Tafel plots can be achieved, assuming that the effective charge of a reactant (+1.6) is significantly lower than it would be expected (zA = +3).

Detection of the fractal character of compact adsorbed layers by the dropping mercury electrode

The development of compact adsorbed layers at the dropping mercury electrode is used for the detection of resulting changes in the geometry of the electrode–solution interface from Euclidean to fractal. A simple size scaling method of the Hg drop surface is applied, which focus on the time dependence of the drop area under conditions of constant adsorbate and base electrolyte concentration, constant potential and constant mercury flow rate. It is found that the slope of the log–log plots of capacitance or capacitance current against electrode surface area or electrode radius is increasing upon the formation of a compact adsorbed layer. Under equilibrium conditions the slope values of the linear log–log plots can be reasonably identified with the fractal dimension of the electrode/solution interface. However, due to the limited extent of the power-law range of the feature vs. scale relation, the size scaling method of the dropping mercury electrode can be used to probe fractal adsorbate films on a strictly qualitative level.

Thermodynamic analysis of (bi)sulphate adsorption on a Pt(1 1 1) electrode as a function of pH

A complete thermodynamic study of (bi)sulphate adsorption on Pt(1 1 1) electrodes from solutions at four different pHs (pH 0.43, 2.1, 3.1 and 4.1) is reported. The effect of pH on the sum of the Gibbs excesses of sulphate and bisulphate species, standard Gibbs energies of adsorption and formal partial charge numbers is analyzed. The results provide relevant information on the nature of species involved in the different voltammetric features. The experiments at pH 0.43 were performed in a higher base electrolyte concentration (0.5 M), that allows the study of (bi)sulphate adsorption in a broader range of concentrations. Under these conditions, two adsorption steps are clearly defined, associated to two different voltammetric features, between 0.30 and 0.60 V and between 0.65 and 0.90 V (standard hydrogen scale, SHE). Once the pH is increased, a marked decrease in absolute value of the (bi)sulphate adsorption Gibbs energy is observed, concomitant with an increasing amount of OH co-adsorption.

Monolayer-Protected Metallic Nanoparticles: Limitations of the Concentric Sphere Capacitor Model

Monolayer-protected clusters (MPC) having metallic core diameters of the order of 1 nm behave as multivalent redox molecules with small capacitances CMPC ≈ 1 aF. Theoretical estimations of this capacitance are usually based on the concentric sphere capacitor model. We have analyzed critically the predictions of this model over a broad range of experimental parameters: the metallic core radius r o , the monolayer thickness d, the charge number z of the metallic core, the dielectric constant of the monolayer e r,m , the base electrolyte concentration c s , and the dielectric constant of the solvent e r,s . To this end, we have solved the nonlinear Poisson-Boltzmann equation taking into account ion penetration. It is shown that the concentric sphere capacitance C o gives the correct order of magnitude as well as some qualitative features of the total MPC capacitance C MPC , although significant deviations are obtained for realistic values of the above parameters, especially when ion and solvent penetration are important. The results obtained are compared with recent theoretical and experimental work by Murray et al. (Anal. Chem. 2005, 77, 2662), Girault et al. (J. Phys. Chem. B 2006, 110, 21460), and Quinn et al. (J. Am. Chem. Soc. 2003, 125, 6644) and provide some extensions of these previous studies.

Electroreduction of Hexaamminecobalt(III) Cation on Bi ( hkl ) Electrodes from Weakly Acidified LiClO4 Solutions

The cyclic voltammetry and rotating disk electrode methods have been used for investigation of electroreduction kinetics of the hexaamminecobalt(III) cations on the electrochemically polished Bi planes. The rate constant for the heterogeneous electroreduction reaction of the cation on the Bi(001) and planes in M aqueous base electrolyte solutions has been established and the results have been compared with the data for the Ag(110), , and Hg electrodes as well as with the data for in M solutions. In the region of zero charge potential, the value of the experimental transfer coefficient is slightly higher than 0.5 and depends on the crystallographic structure of the Bi plane. For more concentrated base electrolyte solutions, the values of apparent transfer coefficient , corrected for the double-layer effect, are practically independent of the base electrolyte concentration and slightly depend on the electrode polarization. Noticeably different values of the double-layer-corrected rate constant and for the Bi(001), , Bi(111), Hg, and Ag(110) electrodes from the data for planes have been explained by the different water and adsorption energies at the metals under discussion.

The kinetics of electroreduction of peroxodisulfate ions on single crystal cadmium and bismuth electrodes

The electroreduction of the peroxodisulfate anions on the electrochemically polished (EP) Cd(0 0 0 1), Bi(1 1 1) and Bi ( 0 1 1 ¯ ) planes has been studied by cyclic voltammetry, rotating disc electrode and impedance methods. The rate constant values of the heterogeneous electroreduction reaction of the S 2 O 8 2 - anion on the EP Cd(0 0 0 1) and Bi( h k l) planes dependent on electrode polarisation and base electrolyte concentration have been calculated. The values of apparent transfer coefficient α app corrected for the double layer effect ( α app ⩽ 0.15) only very weakly depend on the electrode potential and base electrolyte concentration. The very low values of the apparent charge transfer coefficient for S 2 O 8 2 - electroreduction show that the activationless charge transfer mechanism is valid for EP Cd(0 0 0 1) and EP Bi( h k l) electrodes in various surface inactive base electrolyte solutions. This conclusion is in a good agreement with the theoretical models for the high hydrogen overvoltage metals based on the diabatic charge transfer mechanism from the metal to an ion [R.R. Nazmutdinov, D.V. Gluhov, O.A. Petrii, G.A. Tsirlina, G.N. Botikova, J. Electroanal. Chem. 552 (2003) 261].

The kinetics of electroreduction of hexaamminecobalt(III) cation on Bi planes in aqueous HClO 4 solutions

The electroreduction kinetics of hexaamminecobalt(III) cations on electrochemically polished Bi planes has been studied by cyclic voltammetry and rotating disc electrode methods. The rate constant for the heterogeneous electroreduction reaction of the [Co(NH 3) 6] 3+ cation on the Bi(0 0 1), Bi(1 1 1) and Bi( 0 1 1 ̄ ) planes has been established and the results have been compared with the data for the Ag(1 1 0), Au( h k l ) and Hg electrodes [Electrocatalysis, Wiley, New York, 1998, p. 323 (Chapter 8); J. Electroanal. Chem. 498 (2001) 93; J. Am. Chem. Soc. 97 (1975) 4403; J. Electroanal. Chem. 209 (1986) 109; J. Electroanal. Chem. 223 (1987) 171]. In the region of zero charge potential, the value of the experimental transfer coefficient α exp obtained depends on the crystallographic structure of the Bi plane. α exp is only slightly higher than 0.5 for the Bi(1 1 1) and Bi(0 0 1) planes but somewhat lower than 0.5 for the electrochemically most active Bi( 0 1 1 ̄ ) plane. For more concentrated base electrolyte solutions, the values of the apparent transfer coefficient α app corrected for the double layer effect are practically independent of the base electrolyte concentration and depend slightly on the electrode polarisation. Noticeably different values of the double layer corrected rate constant and α app for the Bi(0 0 1), Bi( 0 1 1 ̄ ), Bi(1 1 1), Hg and Ag(1 1 0) electrodes from the data for the Au( h k l ) planes have been explained by the different inner layer structure, i.e. by the different water and ClO 4 − adsorption energies at the metals under discussion.

Electroreduction of hexacyanoferrate(III) anions on electrochemically polished Cd(0 0 0 1) plane

Electroreduction of hexacyanoferrate(III) anion on an electrochemically polished Cd(0 0 0 1) plane in aqueous KF solutions with different additions of K 3[Fe(CN) 6] was studied by rotating disc voltammetry. The rate of electroreduction of [Fe(CN) 6] 3− depends on the electrode potential and base electrolyte concentration. The kinetic current densities obtained have been used for the determination of the rate constant values for the heterogeneous electroreduction reaction of the [Fe(CN) 6] 3− anion on the Cd(0 0 0 1) plane. The diffuse layer potential values ψ d calculated according to the Gouy–Chapman–Grahame (GCG) model have been used for the construction of the corrected Tafel plots, which were linear in the limited region of negative potentials (−1.35 V ≤ ( E− ψ d) ≤ −1.15 V versus Hg|Hg 2Cl 2|4 M KCl) giving the apparent transfer coefficient value α app≈0.35 for 1×10 −3 M KF solution.

The kinetics of electroreduction of peroxodisulfate anion on electrochemically polished Cd(0 0 0 1) plane

The electroreduction of the peroxodisulfate anion on the electrochemically polished (EP) Cd(0 0 0 1) plane has been studied by cyclic voltammetry and rotating disc electrode methods. The rate constant of the heterogeneous electroreduction reaction of the S 2O 8 2− anion on the EP Cd(0 0 0 1) plane dependent on electrode polarisation and base electrolyte concentration has been established. The values of apparent transfer coefficient α app corrected for the double layer effect, noticeably lower than 0.5 for the EP Cd(0 0 0 1) plane, only very weakly depend on the electrode potential but noticeably on the electrolyte concentration, decreasing with the base electrolyte concentration. The very low values of the apparent charge transfer coefficient show that the activationless charge transfer mechanism is probably valid for EP Cd(0 0 0 1) | NaF+ Na 2 S 2 O 8 aqueous solution interface in a good agreement with the theoretical models for the high hydrogen overvoltage metals based on the diabatic charge transfer mechanism from the metal to an ion.

Adsorption of Butyl Acetate on Mercury Electrode and Its Effect on Electroreduction of Zn Cations

Adsorption of butyl acetate on the mercury electrode in 1 M, 0.5 M or 0.1 M NaClO4 is described. Differential capacity curves obtained in these solutions for various butyl acetate concentrations point to the strongest decrease in capacity in 0.1 M NaClO4 for the smallest concentration of the ester tested. At the same time the heights of desorption peaks in the solutions tested decrease in the following order: 1 M > 0.5 M > 0.1 M NaClO4. The obtained results show dynamic competitive adsorption in the ClO4--H2O-ester system. In all the systems studied the zero charge potential values determined with a streaming electrode are shifted towards positive potential with increasing ester concentration. These results suggest that the polar molecule of the ester adsorbs on the mercury electrode with its hydrophobic end while hydrophilic ester group is directed towards the solution. The values of the relative surface excess obtained in the range of potentials where the strong adsorption occurs, virtually do not depend on the base electrolyte concentration. The values of the Gibbs energy of adsorption ∆G0 determined from the Frumkin isotherm have also similar values at base concentrations of the electrolyte tested. The values of interaction constant A are radically different: the adsorbed molecules undergo repulsive force in 1 M NaClO4, whereas in 0.5 M and 0.1 M NaClO4 they are under weak attraction. In the range of more negative potentials, the adsorption layer was investigated following the kinetics of the reduction of Zn++ as a pilot ion. It was stated that the concentration of the base electrolyte fundamentally affects the process: the inhibition of butyl acetate decreases in the order 1 M > 0.5 M > 0.1 M NaClO4.

Electroreduction of peroxodisulfate anion at Bi(111) single-crystal plane electrode

Electroreduction of peroxodisulfate anion on electrochemically polished face Bi(111) in aqueous NaF solution with different additions of Na2S2O8 is studied by rotating-disc voltammetry. The S2O 8 2- electroreduction rate depends on the electrode potential and base-electrolyte concentration, i.e. on the diffuse layer thickness. The kinetic current densities atE = const are obtained by the Koutecky-Levich method and used for the determination of the apparent rate constants of electroreduction of S2O 8 2- . The charge number of the reacting S2O 8 2- species is obtained; it depends on the surface-inactive electrolyte concentration and the electrode potential. The ψ0 potential values at the outer Helmholtz plane, obtained for various NaF + H2O systems according to Gouy-Chapman-Stern-Grahame (GCSG) model, are used for constructing corrected Tafel plots (CTP), which are linear atE- ψ0 < -0.9 V (SCE). The charge transfer coefficient oc for electrochemically polished Bi(111) somewhat decreases with the concentration of the base electrolyte (0.22 ≤α ≤0.27), but the value of α is practically independent of the S2O 8 2- concentration in solution if cNaF = const. However, CTP noticeably depend onc NaF.

Electroreduction of peroxodisulfate anion at a Cd(0001) single-crystal plane electrode

Electroreduction of peroxodisulfate anion on electrochemically polished face Bi(111) in aqueous NaF solution with different additions of Na2S2O8 is studied by rotating-disc voltammetry. The S2O82- electroreduction rate depends on the electrode potential and base-electrolyte concentration, i.e. on the diffuse layer thickness. The kinetic current densities atE = const are obtained by the Koutecky-Levich method and used for the determination of the apparent rate constants of electroreduction of S2O82-. The charge number of the reacting S2O82- species is obtained; it depends on the surface-inactive electrolyte concentration and the electrode potential. The ψ0 potential values at the outer Helmholtz plane, obtained for various NaF + H2O systems according to Gouy-Chapman-Stern-Grahame (GCSG) model, are used for constructing corrected Tafel plots (CTP), which are linear atE- ψ0 < -0.9 V (SCE). The charge transfer coefficient oc for electrochemically polished Bi(111) somewhat decreases with the concentration of the base electrolyte (0.22 ≤α ≤0.27), but the value of α is practically independent of the S2O82- concentration in solution if cNaF = const. However, CTP noticeably depend oncNaF.

Double layer effects in the electrode kinetics of quasi-equilibrium redox reactions

It has been shown that in oxalate solutions the Ru(III)/Ru(II) electrode reaction on the dropping mercury electrode (dme) proceeds under equilibrium conditions with a supporting electrolyte excess, but becomes quasi-equilibrium and, further on, completely irreversible with the gradual decrease in the base electrolyte concentration. These changes in the reversibility of the reaction are in accord with the general concepts of electrochemical kinetics, as it follows from a moment's consideration including the use of the Brönsted rule to describe the double layer structural influence on the kinetics of such quasi-equilibrium reactions. The participation of base electrolyte cations in the elementary act of the studied reaction seems to be most probable in the scope of the accepted outersphere treatment.

Adsorption of 1-alkyl-4-methylpyridinium salts at solid-liquid and water-air interfaces

Determinations of the adsorption at both solid-liquid and water-air interfaces of 1-alkyl-4-methylpyridinium salts have been performed. At the water-air interface, measurements of the surface tension as a function of the bulk concentration of 1-dodecyl-4-methylpyridinium chloride were performed. Mathematical treatment of the resulting isotherm allowed the size of the adsorbed molecule and the CMC to be obtained. The solid adsorbent was a titanium dioxide sample prepared in the laborato Adsorption isotherms of 1-dodecyl-4-methylpyridinium chloride and 1-butyl-4-methylpyridinium chloride were obtained at the same pH and ionic strength. For the shorter-chain surfactant, a second isotherm at a higher base electrolyte concentration was obtained. The experimental isotherms are discussed in the light of literature results and analyzed on the basis of the Frumkin-Fowler-Guggenheim adsorption equation. X-ray photoelectron spectroscopic analyses were performed both on the bare adsorbent and in the presence of the adsorbates. The binding energy of the surfactant elements (both nitrogen and carbon) was observed to undergo significant modifications when the compound was in the adsorbed state. The features of the adsorption of the two organic ions are discussed in light of the different experimental results.

On the potential dependence of the preceding chemical step in the Cd(II) reduction from aqueous KF solutions: a DMμE study

It is shown that the reduction of Cd(II) can be studied using the dropping mercury microelectrode (DMμE) so that the preceding chemical step is kinetically fully rate-determining. Consequently its rate constant can be obtained with good accuracy, which allows us to show that its weak potential dependence can be explained quantitatively using simple double-layer theory. The DMμE voltammogram is shown to vary with base electrolyte concentration in accordance with these ideas.

SERS and Fourier transform SERS studies of the hexacyanoferrate(III)‐hexacyanoferrate(II) couple on gold electrode surfaces

AbstractSurface‐enhanced Raman spectroscopy (SERS) and its Fourier transform (FT) variant were used to study the hexacyanoferrate(III)‐hexacyanoferrate(II) couple at the surface of gold electrodes. The effects of potential, Fe(CN) concentration and base electrolyte (KCl) concentration were measured, and point to distortion of the Fe(CN) ion on the surface of the electrode. The Fe(CN) ion was found not to be strongly adsorbed when a base electrolyte concentration of &gt; 10 mM was used, but the strong adsorption of the Fe(CN) ion was demonstrated. The increased resolution that is possible when using the FT‐SERS technique allows for the partial resolution of bands in the CN stretching region, and thus the construction of a model for the hexacyanoferrate(III) system.