Supporting Electrolyte Solution Research Articles

Rhodamine B-sensitised tin (IV) oxide photo-electrochemical cells: effects of doping, hydroquinone, oxygen and methanol

Rhodamine B-sensitised anodic photocurrents were measured in thin film SnO2 liquid junction cells. The effects of pH, hydroquinone, oxygen and methanol in the supporting electrolyte solution on the sensitisation currents and dark currents were analysed and compared for F-doped and unintentionally doped SnO2 electrodes. Photocurrents were generally smaller in the F-doped SnO2 electrodes than in the unintentionally doped electrodes, due to a narrow depletion region and impurity states which may give rise to electron back-tunnelling. However, the presence of the reducing agent hydroquinone caused photocurrents to be of similar magnitude in the two types of anodes, by preventing back-tunnelling in the highly doped SnO2. In addition, the presence of O2, and oxidising agent, suppressed the photocurrent in the undoped electrode, while causing an enhancement of the sensitised photocurrent in the doped electrode, particularly in the presence of 15-25% methanol.

クロルプロマジンの電極酸化反応に及ぼす共存電解質の影響

A comparison of the rate constants (kobs) of the chemical reactions which occure after the electrochemical oxidation of chlorpromazine (CPZ) to CPZ cation radical (CPZ) in various supporting electrolyte solutions was made. In solutions containing bivalent anions (such as phosphate, sttccinate and glutarate solutions)the kobs's obtained by rotating disk voltammetry were larger than those in solutions containing monovalent anions (like an acetate solution). The rate constant depended on the structure of the anion.

The reduction of Cr(III) in concentrated aqueous electrolytes at a DME

Abstract The reduction of Cr(III) at a dropping mercury electrode is studied in the presence of highly concentrated NaCl, NaI and Na2SO4 solutions. Thermodynamic analyses of the interface in the supporting electrolyte solutions are also performed in order to account for the double-layer contributions to the reaction rates. The results can be rationalized better fi the relative surface excesses are corrected for the amount of adsorbed water and if the discharge plane is situated outside the OHP. The reactivities in NaI solutions are higher than those in NaClO4 at the same concentration but they are equal when compared at the same water activity. Lower rate constants are observed in NaCl and Na2SO4 solutions, which are explained on the basis of ion-pair associations in the bulk of the solution.

Researches on chemically modified electrodes

A novel electrochromic film of vanadium hexacyanoferrate (VHF), an analogue of mixed-valence-compound Prussian blue, was deposited electrochemically on a platinum substrate for the first time. The preparative conditions, electrochemical properties and infrared spectra of the VHF film were investigated in detail. The VHF film modified electrode gave three couples of redox waves by cyclic voltammetry (CV) in a supporting electrolyte solution of H2SO4 and K2SO4, with midwave potentials (Em = (Epa + Epc)/2) of 0.90, 0.98, and 1.06 V (vs. KCl sat. Ag/AgCl), respectively. Reversible color switches with a sharp contrast between yellow, green and blue can be observed successively. The corresponding electrochemical reactions are considered as follows: Waves at 0.90 V: M+V3+FeII(CN)6 + H2O + M+ ⇌ M+2VO2+FeII(CN)6 + e− + 2 H+ Waves at 0.98 V: M+2VO2+FeII(CN)6 + H2O ⇌ M+2(VO2H)+FeIII(CN)6 + e− + H+ Waves at 1.06 V: M+2(VO2H)+FeIII(CN)6 ⇌ M+2(VO2)+FeIII(CN)6 + e− + H+ Both the metallic M+ (which can be K+, Na+ or Li+) and the hydrogen ion H+ participate in the redox process, while anions do not. The electrochemical stability of the VHF film on platinum is quite good. Only a small reduction in the peak current of the VHF film modified electrode was observed through one thousand cycles of continuous potential scanning. The infrared spectra of the film are very similar to those of Prussian blue but considerably diffrent from those of the Na3VO4 and K3Fe(CN)6 from which the film was made.

Background subtraction for rapid scan voltammetry

Methods for the elimination of residual current in fast scan (> 300 V s −1) voltammetry have been evaluated at microvoltammetric electrodes. Staircase voltammetry is found to give only a modest improvement in the ratio of the faradaic current to the residual current. Supeior results are obtained when the residual current, obtained in supporting electrolyte solution, is digitally subtracted from the voltammogram obtained in the presence of the electroactive species. The subtraction process is facilitated by conducting the whole experiment in a flow injection apparatus so that the electrode remains in solution while the two voltammograms are obtained. Undistorted voltammograms have been obtained for the reduction of anthracene (∼ 2 m M) at scan rates up to 10,000 V s −1. At 300 V s −1, virtually undistorted voltammograms are obtained for the reduction of Tl + at low concentration (20 μ M) in aqueous solution at a mercury microvoltammetric electrode. Analog offset of the residual current was used to improve the dynamic range. The limits of this technique are caused by the electronic noise in the ideal case where flat residual current curves are obtained.

Factors Affecting the Zeta Potential at Wool Fiber Surfaces

A streaming potential method has been used to determine the zeta potential at the surface of wool fibers in a supporting electrolyte solution. The zeta potential gives a measure of the average charge density at the surface of shear and, when measured as a function of pH, yields a titration curve for the fiber surface. The reproducibility of the curves for a particular wool sample is now such that zeta potential determination provides a means of assessing chemical reactions at the fiber surface through changes in surface charge. The technique has been applied to studies of the chlorine/Hercosett shrinkproofing process. The shapes of the curves and the pH of the isoelectric point can be significantly affected by the choice of cleaning procedures adopted to remove contaminants. In addition, the state of the surface changes with time; this aging process leads to a more negative surface through atmospheric oxidation. Chemical oxidation by acid chlori nation of disulphide groups brings about a large excess of anions and a negative surface. Subsequent modification by deposition of a cationic polymer, as in the chlorine/ Hercosett process, results in a more positive surface. However, the interaction between the polymer and the wool causes the new surface to be less positive than for Hercosett film coated on a glass substrate.

Purification of Supporting Electrolyte by a Moderate Current Pre-Electrolysis Potentiostat

ABSTRACT Anodic stripping voltammetry (ASV) is a well known technique for determining ppb levels of metal ions in environmental samples. One problem in the determination of metal ions at this low concentration level is the contribution of comparatively large amounts of metal ions originating from supporting electrolyte that is added to the sample and used to prepare standards. Pre-electrolysis has been found to reduce the heavy metal content in supporting electrolyte solutions to a few ppb. A moderate current, low cost, potentiostat and an electrochemical cell have been developed for the purification of supporting electrolytes by pre-electrolysis. It provides the moderate current needed at the start of the electrolysis especially during double layer charging as well as the small faradaic current needed through the duration of the electrolysis.

ジメチルスルホキシド中におけるビス（１，３‐ジアルキル‐１，３‐プロパンジオナト）ニッケル（ＩＩ）錯体のポーラログラフィー

The polarography of three bis(1, 3-dialkyl-1, 3-propanedionato)nickel(II)complexes, viz., [Ni(acac)2], [Ni(dppm)2], and [Ni(dpm)2], was studied in dimethyl sulfoxide solution c ontaining one of the supporting electrolytes of NaClO4, TMAP, or TBAP of 0.05 mol⋅dm-3 in concentration, where acac-, dppm-, and dpm- mean the enolate anions of acetylacetone, d i propionylmethane, and dipivaroylmethane respectively. The polarographic behavior of [NiT(acac)2] in all the supporting electrolyte solutions and that of [Ni(dppm)2] and [Ni(dpm)2] in MAP and TBAP solutions were explained by the electrode reaction given in Scheme 1.The dissolved state of ten bis(β-diketonato)nickel(II) complexes was related to the properties of their ligands, where seven complexes had been studied by us.

Polymer films on electrodes: Part XV. The incorporation of Ru(bpy) 2+3 into polymeric films generated by electrochemical polymerization of 2,2'-bipyrazine (bpz) and Ru(bpz) 2+3

Modified glassy carbon electrodes have been prepared by anodic oxidation of solutions of Ru(bpz) 2+ 3 (bpz = 2,2'-bipyrazine) or bpz. A measurement of film resistance indicates ϱ = ∼10 6 ω for the ‘bpz’ film. These electrodes readily incorporate Ru(bpy) 2+ 3 (bpy = 2,2'-bipyridine) and cyclic voltammetry in pure supporting electrolyte solution yields reversible redox waves corresponding to the Ru(bpy) 3+ 2+ 3 couple. The thickness of films deposited by the above technique can be systematically varied by altering the duration of electropolymerization, and the surface concentration of incorporated Ru(bpy) 2+ 3 varies accordingly. The cyclic voltammograms exhibit surface film behavior for the thin films while the behavior for thick films is diffusional in nature (apparent diffusion coefficient, D app = 2.2 × 10 −9 cm 2/s for films ∼ 1.6 μm thick). The concentration of surface-confined polypyridyl complex can be as high as 3.5 × 10 −8 mol/cm 2 of electrode area (i.e., an effective bulk concentration of 0.22 M for a 1.6 μm film) but gradual loss of electroactive material is observed upon cycling the potential between the redox waves. The loss of material does not occur, however, in 5 × 10 −5 M Ru(bpy) 2+ 3. Incorporation of Ru(bpy) 2+ 3 from solutions at pH 10.5 led to voltammograms with an additional reversible couple ( E 1 2 = 0.69 V vs. SSCE), believed to arise from the decomposition of Ru(bpy) 3+ 3 at high pH. Electrogenerated Ru(bpy) 3+ 3 in the film reacts with oxalate ions in solution to produce chemiluminescence. The films are completely porous to hydroquinone dissolved in the supporting electrolyte (0.05 M phosphate buffer; 0.1 M Na 2SO 4; pH 4.8) and the hydroquinone—quinone couple is considerably more reversible at these modified electrodes; however, a similar increase in reversibility is observed at the bare electrode following anodization in 7 M H 2SO 4.

Decrease in the Quantum Efficiency of a Cadmium Sulfide Photoanode Due to Sulfur Deposition. Determination of Quantum Efficiency by Temperature Measurement

Abstract CdS photoelectrodes dissolve during photoanode reactions in a supporting electrolyte solution, and the quantum efficiency changes due to sulfur deposition. Temperature measurement technique has been used in this work to determine the quantum efficiency of the CdS photoelectrode. It has been found that decreases in the quantum efficiency can be monitored easily by this method.

Underpotential alloy formation in the system Ag( hkl)/Cd 2+

The underpotential deposition (UPD) of Cd on “real” and “quasi-ideal” silver single crystal surfaces of (111) and (100) crystallographic orientation as well as on polycrystalline silver substrate has been investigated in 0.5 M Na 2SO 4 supporting electrolyte solutions. At high underpotentials 100 < Δ E < 350 mV, the UPD is characterized by a quasi-reversible adsorption/desorption of Cd whereas at low underpotentials. Δ E < 50 mV, an increase of the anodic stripping charge with the polarization time is found due to the formation of an AgCd alloy at the substrate surface. The time dependence of this process can be described by a parabolic rate law, the rate constant of which is a function of Δ E and temperature T. Relatively low activation energies of about 70 kJmol −1 were determined from measurements at 293 ⩽ T ⩽ 338 K. The results are discussed in terms of a semi-infinite-linear diffusion model. The alloy formation process is assumed to be initiated by a place exchange between Ag substrate atoms and vacancy sites within a mobile Cd adsorbate layer thus forming the initial stage of a highly distorted AgCd alloy. The further growth will take place by the movement of Ag atoms through the vacancy-rich surface alloy and the simultaneous deposition of Cd at the interface AgCd/Cd 2+.

Voltammetric Studies of the Use of the Rotated Oxide Electrode as an Indicator Electrode and as a View to the Determination of EDTA and Other Complexanes

Abstract The accessible potential ranges of rotated lead dioxide (PbO2) and manganese dioxide (MnO2) electrodes were investigated in supporting electrolyte solutions of 0.1 mol/1 (mol/dm3) KNO3 at various pH values, by measuring the base currents of these oxide electrodes. The anodic and cathodic ascending potentials of both the oxide electrodes are pH-independent in a neutral solution. In each neutral system of KNO3, KClO4, K2SO4, and KCl, the accessible potential range of the PbO2 electrode was from +1.4 to +0.2 V vs. SCE, while that of the MnO2 electrode was from +1.2 to +0.3 V, and the lower manganese oxide electrode from +0.3 to −0.9 V. Furthermore, the applications of these electrodes to the determination of EDTA and other complexanes were examined. Both the oxide electrodes gave a good calibration curve which could establish a linear relationship to the EDTA concentration, passing through the point of origin. The rotated PbO2 and MnO2 electrodes seem to be useful for determining depolarizers such as the EDTA-type complxanes.

The Reduction of Hexakis(urea)chromium(III) Ions at the Dropping Mercury Electrodes

Abstract The polarographic reduction of hexakis(urea) chromium (III) ions at the dropping mercury electrode has been studied in various supporting electrolyte solutions. This complex exhibits two irreversible reduction waves; the first corresponds to Cr(III)→Cr(II), and the second, to Cr(II)→Cr(0). The kinetic parameters of the electrode reactions were determined in various supporting electrolyte solutions and at varied ionic strengths by means of Tast polarography. The differential-pulse polarographic characteristics of this complex are also given.

Effects of anions on the reflection spectroscopic behavior of the multiple states of h chemisorption at platinum electrodes

In sufficiently pure solutions and especially at relatively low concentrations, four or five states of chemisorbed H can be resolved at Pt electrodes below the limit of monolayer coverage, even on single crystals. The distribution of the chemisorbed H amongst the states of different energies of adsorption depends on the anion of the supporting electrolyte solution and indirectly the pH; it also depends significantly on the nature of co-adsorbed cations. Reflection spectroscopic studies have been carried out over a range of wave-lengths in the visible and near uv spectrum in an attempt to establish if the distinguisable states of H chemisorption have characteristic optical as well as electrochemical features. Although the quantities of adsorbed H in the various energy states depend on specific adsorption of both ions of the electrolyte, several of the states have a characteristic reflection spectrum at Pt.

Determination of electrochemical kinetic parameters by square-wave polarography Polarographic reduction of Zn(II) in concentrated nitrate and perchlorate supporting electrolyte solutions

The electrochemical kinetic parameters for the polarographic reduction of Zn(II) at a dropping mercury electrode in concentrated supporting electrolytes consisting of sodium, ammonium, lithium, magnesium and calcium nitrates and sodium perchlorate have been determined at 25.0±0.1°C by the square-wave polarographic method. The rate parameter decreased with increase of radius of the alkali-metal cations present in the electrolyte and with increase of charge of the cation of the electrolyte in solution of the same ionic strength. It also decreases, passes through a minimum and then increases with the increase in the concentration of any of the supporting electrolytes. The initial decrease is ascribed to the Frumkin double-layer effect but the latter increase has been explained in terms of the change in the activity of water around the electrode.

Determination of electrochemical kinetic parameters by square-wave polarography: Polarographic reduction of Zn(II) in concentrated nitrate and perchlorate supporting electrolyte solutions

The electrochemical kinetic parameters for the polarographic reduction of Zn(II) at a dropping mercury electrode in concentrated supporting electrolytes consisting of sodium, ammonium, lithium, magnesium and calcium nitrates and sodium perchlorate have been determined at 25.0±0.1°C by the square-wave polarographic method. The rate parameter decreased with increase of radius of the alkali-metal cations present in the electrolyte and with increase of charge of the cation of the electrolyte in solution of the same ionic strength. It also decreases, passes through a minimum and then increases with the increase in the concentration of any of the supporting electrolytes. The initial decrease is ascribed to the Frumkin double-layer effect but the latter increase has been explained in terms of the change in the activity of water around the electrode.

Phosphate sorption curves as a soil testing technique: A simplified approach

Abstract Single point phosphate sorption curves effectively estimated phosphate fertilizer requirements while requiring less work than multiple point curves. Correlation coefficients of 0.961 and 0.981 were obtained when phosphate rates, estimated using single point curves, were compared with those from multiple point curves. Reducing the ionic strength of the supporting electrolyte solution by using 0.001 M CaCl2 or water rather than 0.01 M CaCl2 during equilibration increased dissolved inorganic phosphate 73% and 141% on the average thus improving analytical precision. The relative effects of salt concentration were sufficiently independent of pH and phosphorus concentration to suggest that a simple conversion factor can be used to convert external P requirements from one set of equilibrium conditions (salt concentration) to another.

Adsorption properties of polycrystalline and single crystal electrodes and the influence of surface inhomogeneity

It is shown that the adsorption of some neutral organic compounds on individual faces of a zinc single crystal can be described by the Frumkin-Damaskin theory with the use of the two parallel capacitors model. For a polycrystalline electrode a departure from the two parallel capacitors model is observed which is due to the energetic inhomogeneity of the surface. A method is suggested for calculation of the adsorption isotherm, and of the dependence of the surface coverage θ on the potential of a polycrystalline electrode, from capacity measurements data under the condition that for all n crystallographic faces (grains) exposed on the surface, the difference ( C on − C′ n) is the same ( C on and C′ n are the double layer capacities in the supporting electrolyte solution and at θ = 1 of the n-th face, respectively). An adsorption isotherm is proposed for a uniformly inhomogeneous surface which takes account of the attractive interaction between adsorbate particles. Some methods are suggested for evaluation of the surface inhomogeneity factor ( f). This factor has been determined from adsorption data for cyclohexanol and n-amyl alcohol. The differential capacity curves measured on polycrystalline zinc in the presence of cyclohexanol are in good agreement with the calculated curve for a uniformly inhomogeneous surface.

Adsorption properties of polycrystalline and single crystal electrodes and the influence of surface inhomogeneity

It is shown that the adsorption of some neutral organic compounds on individual faces of a zinc single crystal can be described by the Frumkin-Damaskin theory with the use of the two parallel capacitors model. For a polycrystalline electrode a departure from the two parallel capacitors model is observed which is due to the energetic inhomogeneity of the surface. A method is suggested for calculation of the adsorption isotherm, and of the dependence of the surface coverage θ on the potential of a polycrystalline electrode, from capacity measurements data under the condition that for all n crystallographic faces (grains) exposed on the surface, the difference (Con − C′n) is the same (Con and C′n are the double layer capacities in the supporting electrolyte solution and at θ = 1 of the n-th face, respectively). An adsorption isotherm is proposed for a uniformly inhomogeneous surface which takes account of the attractive interaction between adsorbate particles. Some methods are suggested for evaluation of the surface inhomogeneity factor (f). This factor has been determined from adsorption data for cyclohexanol and n-amyl alcohol. The differential capacity curves measured on polycrystalline zinc in the presence of cyclohexanol are in good agreement with the calculated curve for a uniformly inhomogeneous surface.

Analytical chemical studies on electrode processes by column coulometry: I. Basic studies on the column electrode

Summary The basic characteristics of the column electrode have been investigated to elucidate mechanisms of electrode reactions by using this method. Carbon fiber of about 10 μm in diameter was used for the working electrode. When the electrode rate constant is faster than 10−2 cm−1 s the electrode process shows reversible characteristics and when the constant is slower than 10−3 cm s−1 the process shows irreversible characteristics. The transfer coefficient of an electrode reaction can be obtained by changing the flow-rate of the supporting electrolyte solution. The rate constant of an electrode reaction can also be obtained relatively. By using the proposed method, electrode processes of copper have been investigated and results similar to those of the ring-disk electrode polarography were obtained.