Electrochemical study of chitosan films deposited from solution at reducing potentials

We report the electrochemical characterization of chitosan films deposited at gold electrodes from an acidic solution at reducing potentials. Cyclic voltammetry was used to characterize the deposition and electroactivity of chitosan coated gold electrodes. Chitosan films were found to deposit at gold electrodes at potentials more negative than −1.0 V versus Ag/AgCl, a potential associated with the onset of water reduction and increase in pH near the electrode. The chitosan films are electrochemically inactive; similar background charging currents are observed at bare gold and chitosan coated electrodes. The chitosan films are permeable to both cationic [Ru(NH₃)₆^3+/2+] and anionic [Fe(CN)₆^3−/4−] redox couples, but anionic complexes are retained in the chitosan film. Semiintegral analysis was used to examine adsorbed redox species at the chitosan coated electrode surface. Electrochemical parameters, including apparent diffusion coefficients for the redox probes at the electrodeposited chitosan modified electrodes are presented and are comparable to values reported for cast chitosan films.     

Electrochemical and spectroscopic characterization of poly(1,8-diaminocarbazole): Part II. Electrochemical, in situ vis/NIR and Raman studies of redox reaction of PDACz in protic and aprotic media

Electrochemical redox reactions of poly(1,8-diaminocarbazole) (PDACz) films in aqueous (0.1 M HClO₄) and nonaqueous (0.1 M LiClO₄ in acetonitrile) solutions were studied by cyclic voltammetry, in situ vis/NIR and Raman spectroscopy. It has been demonstrated that spectroelectrochemical behavior of the polymer is strongly dependent on the nature of the solution used for doping-undoping but not on the medium used for electropolymerization. A redox couples Fe²⁺/Fe³⁺, Fe(CN)₆^4−/3− and tertrathiafulvalene were used as the probes for the studies of electroactivity of the oxidized polymer films. The results were discussed in terms of different mechanism of deprotonation process of the polymer in aqueous solution of 0.1 M HClO₄ and in 0.1 M LiClO₄ solution in aprotic acetonitrile and the reaction schemes in the two media are proposed.     

Electrochemical and spectral studies on the catalytic oxidation of nitric oxide and nitrite by high-valent manganese porphyrins at an ITO electrode

Catalytic oxidation of nitric oxide and nitrite by water-soluble manganese(III) meso-tetrakis(N-methylpyridinium-4-yl) porphyrin (Mn(III)(4-TMPyP) was first studied at an indium-tin oxide (ITO) electrode in pH 7.4 phosphate buffer solutions. A stepwise oxidation of Mn(III)(4-TMPyP) through high-valent manganese porphyrin species has been observed by electrochemical and spectroelectrochemical (OTTLE) techniques. The formal potential of 0.63 V for the formation of OMn(IV)(4-TMPyP) has been estimated from OTTLE data. The product, oxoMn(IV) porphyrin, was relatively stable decaying slowly to Mn(III)(4-TMPyP) with a first-order rate constant of 3.7 × 10⁻³ s⁻¹. OMn(IV)(4-TMPyP) has been found to oxidize NO catalytically at potentials about 70 mV more negative than that previously reported for OFe(IV)(4-TMPyP) with good selectivity against nitrite. Nitrite was catalytically oxidized at potentials higher than 1.1 V presumably by OMn(V)(4-TMPyP). OMn(IV)(4-TMPyP) was observed as an intermediate species. Nitrate has been confirmed to be a final product of the electrolysis at 1.2 V, while at 0.8 V nitrite left unchanged, demonstrating that OMn(IV)(4-TMPyP) could not oxidize nitrite. A possible schemes of the catalytic oxidation of NO by OMn^IV(4-TMPyP) and NO₂⁻ by OMn(V)(4-TMPyP) have been proposed.     

Electrosynthesis and spectroelectrochemical characterization of poly(3,4-dimethoxy-thiophene), poly(3,4-dipropyloxythiophene) and poly(3,4-dioctyloxythiophene) films

Poly(3,4-dialkoxythiophene) films with different length of alkyl chain (1,3 and 8 carbon atoms) were obtained on Pt and ITO electrodes from the monomer solutions in acetonitrile by cyclic voltammetry (CV). The properties of the resulting films were studied by electrochemical methods, UV-Vis, FTIR and NMR spectra. The CVs were correlated with differential cyclic voltabsorptograms (DCVA) recorded at the absorption maxima to explain the shape of the voltammograms of the polymers studied, dependent on the alkyl-chain length in alkoxy group. The presence of the zones of different crystallinity in the polymer film was postulated. Significant influence of the type of the solvent on asymmetry of the cyclic voltammograms for the polymer doping-undoping has been discussed in terms of the solvent interaction with radical cation (polaron) delocalized on the alkoxy side groups. The polaron delocalization was proved by ¹H-NMR spectra. Appearance of infrared activated vibrations (IRAVs) in the range 1500-600 cm⁻¹ and a characteristic electronic band at 3300 cm⁻¹ at the polarization potential +0.25 V versus Ag/Ag⁺ and their gradual changes upon further polymer oxidation were interpreted in terms of evolution of different charge carriers in lightly and heavily doped polymer.     

The photoelectrocatalytic oxidation of aqueous nitrophenol using a novel reactor

This paper reports the oxidation of aqueous 4-nitrophenol solutions in a photo-electrochemical bubble column reactor (BCR) in which mass transfer has been shown not to be rate limiting. The work represents the first steps in the scale-up of active photoanodes and efficient reactors for the disinfection and detoxification of water. The preparation, optimization and application of two types of electrode are described and the results are compared with those for a TiO₂ electrode supplied by Ineos Chlor. Photocurrents measured in tap water and in aqueous methanol were used for the initial characterization of the electrodes. The methanol was employed for diagnostic purposes only, as discussed below; methanol can react either by direct hole transfer or by hydroxyl radical recombination, but the balance of these reactions depends upon the nature of the electrode surface. The most active thermal electrodes were fabricated by heating titanium metal in air at 750 °C for 10 min, whilst the most active sol–gel electrodes were heated at 600 °C for 10 min. Three of the central achievements of the work were to: (1) show that it is possible to design and fabricate photoelectrochemical reactors capable of effecting the mineralization of strongly absorbing organics; (2) confirm that the photocatalytic decomposition of 4-NP in reactors with a 4 dm³ capacity can be increased by the application of a small positive potential and (3) that the application of such a potential significantly enhances the mineralization of 4-NP. For the mineralization of 0.25 mM nitrophenol solutions the reactivity sequence is: Photoelectrocatalytic > Photocatalytic > Photochemical > Electrochemical. However, even at 3 V applied potential, charge recombination is not eliminated. The order of electrode activity was: Ineos > Sol Gel > Thermal. Differences between the activities of different electrodes were attributed to changes in the structure and morphology of the TiO₂. It is noteworthy that although, for nitrophenol oxidation, the thermal electrodes were the least active, for photoelectrocatalytic disinfection in the same type of reactor, thermal electrodes were the most active.     

Electrochemical dissolution of calaverite(AuTe2) in thiourea acidic solutions

Cyclic voltammetric studies of carbon paste electrodes of a synthetic gold telluride, calaverite (AuTe2), in acidic aqueous thiourea solutions indicate that for potentials of about 0.4V vs SCE adsorbed thiourea decomposes to formamidine disulphide, while gold from calaverite oxidizes and complexes with thiourea. The chemical oxidation of calaverite with the formamidine disulphide produced occurs in parallel with these electrodic processes. Additionally, for potentials in the vicinity of 0.5V vs SCE tellurium from calaverite transforms to telluril ion, HTeO+2. A passive film of tellurous acid H2TeO3 forms at potentials around 0.7 V vs SCE whereas at potentials above 0.9 V vs SCE the formation of gold oxides and hydroxides is apparent. Reduction of calaverite occurs at potentials less than –0.7 V vs SCE. Other cathodic peaks are associated to the reverse processes of the anodic decomposition stages.     

The characterization and bioelectrocatalytic properties of hemoglobin by direct electrochemistry of DDAB film modified electrodes

Direct electrochemistry of hemoglobin can be performed in acidic and basic aqueous solutions in the pH range 1-13, using stable, electrochemically active films deposited on a didodecyldimethylammonium bromide (DDAB) modified glassy carbon electrode. Films can also be produced on gold, platinum, and transparent semiconductor tin oxide electrodes. Hemoglobin/DDAB films exhibit one, two, and three redox couples when transferred to strong acidic, weak acidic and weak basic, and strong basic aqueous solutions, respectively. These redox couples, and their formal potentials, were found to be pH dependent. An electrochemical quartz crystal microbalance and cyclic voltammetry were used to study the in situ deposition of DDAB on gold disc electrodes and hemoglobin deposition on DDAB film modified electrodes. A hemoglobin/DDAB/GC modified electrode is electrocatalytically reduction active for oxygen and H₂O₂, and electrocatalytically oxidation active for S₂O₄²⁻ through the Fe(III)/Fe(II) redox couple. In the electrocatalytic reduction of S₄O₆²⁻, S₂O₄²⁻, and SO₃²⁻, and the dithio compounds of 2,2′-dithiosalicylic acid and 1,2-dithiolane-3-pentanoic acid, the electrocatalytic current develops from the cathodic peak of the redox couple at a potential of about −0.9 V (from the Fe(II)/Fe(I) redox couple) in neutral and weakly basic aqueous solutions. Hemoglobin/DDAB/GC modified electrodes are electrocatalytically reduction active for trichloroacetic acid in strong acidic buffered aqueous solutions through the Fe(III)/Fe(II) redox couple. However, the electrocatalytic current developed from the cathodic peak of the redox couple at a potential of about −0.9 V (from the Fe(II)/Fe(I) redox couple) in weak acidic and basic aqueous solutions. The electrocatalytic properties were investigated using the rotating ring-disk electrode method.     

Electrooxidation of stainless steel AISI 304 in carbonate aqueous solution at pH 8

The electrochemical behaviour of stainless steel AISI 304 (SS304) has been investigated in deaerated 0.1–1 m NaHCO₃ solutions at pH 8 using a rotating disc electrode. The polarization curves are characterized by a broad range of passivity at low potentials (–0.8 to 0.3 V), a depassivation region at 0.4 V vs SCE and, at high potentials (0.5 to 0.85 V), a passive region before oxygen evolution. In the low potential range, the SS304 electrode behaves like a Cr-rich metallic phase, and the dissolution of Fe²⁺ ions into the solution is hindered by the formation of a Cr₂O₃ layer. As the potential reaches 0.4V, the oxidation-dissolution of Cr(iii) oxide/hydroxide to CrO₄ ² ions occurs, with the participation of bicarbonate/carbonate as a catalyst in the dissolution reaction. Since the chromium oxide/hydroxide dissolution and subsequent surface enrichment of iron oxides occur, the applied potential, exposure time and oxidation charge have a considerable effect on the passive film properties. At high potentials, the presence of a passive film of iron oxides/hydroxides or oxyhydroxides plays a key role in the SS304 passivity with the presence of Fe(vi) species incorporated or adsorbed into the passive films. Colouration of the SS304 surface is observed in the second passive region. A film of a uniform gold colour formed on SS304, mild steel 1024 and iron in carbonate and borate solutions at pH 8. The colour of the electrode surfaces remain unchanged in air and in solutions at positive potential but it disappears at open-circuit potential or is easily reduced in the first negative-going potential scan.     

High catalytic activity of chemically activated gold electrodes towards electro-oxidation of methanol

Electro-oxidation of methanol has been investigated on activated, rough gold electrodes in alkaline solutions. The electrodes were activated by formation and decomposition of gold amalgam. The oxidation of methanol starts at potentials about 400 mV less positive as compared with smooth poly and single crystal gold electrodes and the oxidation current is much higher. For freshly prepared, activated gold electrodes the oxidation current is similar to that obtained on smooth platinum, however it diminishes with time. The formation of small crystallites, which could trap OH⁻ anions, seems to be the most important factor for this unusual catalytic activity. The dependence of the oxidation process on electrode topography is discussed.     

Electrochemical properties of porous bismuth electrodes

The properties of Bi surfaces with different roughnesses were characterized by electron microscopy, cyclic voltammetry, and impedance spectroscopy. Two different strategies were used for preparation of porous bismuth layers onto Bi microelectrode surface in aqueous 0.1 M LiClO₄ solution. Firstly, treatment at potential E < −2 V (vs. Ag|AgCl in sat. KCl) has been applied, resulting in bismuth hydride formation and decomposition into Bi nanoparticles which deposit at the electrode surface. Secondly, porous Bi layer was prepared by anodic dissolution (E = 1 V) of bismuth electrode followed by fast electroreduction of formed Bi³⁺ ions at cathodic potentials E = −2 V. The nanostructured porous bismuth electrode, with surface roughness factor up to 220, has negligible frequency dispersion of capacitance and higher hydrogen evolution overvoltage than observed for smooth Bi electrodes.     

Adsorption of thiourea on monocrystalline silver electrodes in neutral solution

Impedance spectroscopy and radiometric method have been used in the study of thiourea (TU) adsorption on monocrystalline silver electrodes of basal indices: (1 1 1), (1 0 0) and (1 1 0) in neutral solution. The dependence of the surface concentration of TU on the electrode potential and on the bulk concentration was determined for each studied surface. From radiometric measurements it follows that adsorption of TU on silver electrodes takes place in the entire range of applied potentials. The process of adsorption is practically reversible with respect to the electrode potential (in the range of the double layer) and the bulk concentration of TU. Differential capacity of silver electrodes in 0.01 M NaClO₄ solution containing TU of concentrations from 10⁻⁶ to 5 × 10⁻⁴ M has been measured. The isotherms of TU adsorption, determined from the capacitance and radiometric measurements have been compared and the Gibbs energy of adsorption was calculated. The values of limiting surface concentration of adsorbed TU as well as the Gibbs energy of adsorption depend on the plane of Ag electrode and follow the sequence: Ag(1 1 1) > Ag(1 0 0) > Ag(1 1 0) which is in agreement with the surface density of Ag atoms.     

Electrochemistry and ion-sensing properties of calix[4]arene derivatives

The cyclic voltammetric properties of several substituted calix[4]arenes were examined in acetonitrile and dichloromethane. The compounds that contained one phenolic group in the macrocyclic cavity were able to be electrochemically oxidised at positive potentials. In acetonitrile, cyclic voltammetry experiments indicated that the phenolic compounds were oxidised in a two-electron (one-proton) process over all measured scan rates (up to 50 V s⁻¹), while in dichloromethane, the oxidation process occurred by one-electron at scan rates ≥5 V s⁻¹, to most likely form the radical cations. In both solvents, longer timescale (minutes to hours) controlled potential coulometry experiments indicated that the oxidation process occurred by two-electrons per molecule, to form reactive diamagnetic cations that could not be reduced back to the starting materials under electrolysis conditions. The ion-sensing properties of the compounds were investigated in polymer membrane ion-selective electrodes and it was found that they responded reversibly in a Nernstian fashion to Groups 1 and 2 metals and had the highest selectivity to the cesium cation.     

Electrochemical modification of glassy carbon electrode by poly-4-nitroaniline and its application for determination of copper(II)

Electrochemical modification of glassy carbon (GC) electrode by poly-4-nitroaniline (P4NA), electrochemical reduction of P4NA and applicability of electrode modified in this way for determination of copper(II) (Cu(II)) is reported in this study. Electrochemical surface modification was performed by cyclic voltammetry in the potential range between +0.9 V and +1.4 V vs. Ag/Ag⁺ (in 10 mM AgNO₃) at the scan rate of 100 mV/s by 100 cycles in non-aqueous media. In order to provide electrochemical reduction of nitro groups on the P4NA-modified GC electrode surface (P4NA/GC), the cyclic voltammograms inducing/evidencing the reduction of nitro groups were performed in the potential range between −0.1 V and −0.8 V vs. Ag/AgCl/(sat.KCl) at the scan rate of 100 mV/s. The reduced P4NA/GC surfaces (Reduced-P4NA/GC) were treated with aqueous solution of nitrilotriacetic acid. The sensitivity of GC electrode modified in described way towards Cu(II) was investigated in Britton-Robinson buffer solution, pH 5.0. The potentiometric generic pulse technique was applied as innovative electrochemical method for detection of analytical signal. It was shown that GC electrodes modified in here described way will be suitable for the determination of Cu(II) in technological waste water and/or some other solutions containing Cu(II) ions.     

Electrochemical surface nanopatterning by selective reductive desorption from mixed metal surfaces

We report on a novel strategy to the functionalisation of electrode surfaces based on the preparation and patterning of mixed metal electrodes using metal selective electrodesorption of a sacrificial alkanethiol. Plain palladium (Pd) and plain polycrystalline gold (poly-Au) electrodes were used initially to determine metal specific potential windows within which electrodesorption of the short alkanethiol mercaptoethanol could be achieved. We found that stripping of mercaptoethanol from gold was achieved at potentials lower than −0.800 V, whilst stripping from palladium was achieved at more positive potentials i.e. around −0.650 V. Mixed metal electrodes were prepared by electroplating for short period of times palladium onto poly-Au electrodes. The resulting surfaces were characterised electrochemically in 1 M H₂SO₄ and clearly exhibited reduction peaks for both gold and palladium oxide formation. The mixed metal electrodes were coated with mercaptoethanol, which was further selectively removed from Pd by cyclic voltammetry in NaOH in the Pd-specific potential window. The presence of bare Pd domains revealed following electrodesorption was confirmed by subsequently adsorbing the electroactive alkanethiol 6-ferrocenylhexanethiol onto the freshly revealed Pd. Cyclic voltamogramms exhibited sharp redox peaks that could only be attributed to the successful immobilisation of 6-ferrocenylhexanethiol onto fresh Pd domains. Control surfaces, i.e. MCE fully coated Pd/Poly-Au electrode, exposed to 6-ferrocenylhexanethiol did not exhibit significant voltammetric features, attesting to the efficient patterning of the mixed metal electrode by employing metal specific reductive desorption of short alkanethiols. The possibility to pattern electrode surfaces in such way will find application in the field of diagnostics, and also in heterogeneous catalysis where Pd-Au alloys have received an increased interest in the recent years.     

Electrochemical synthesis of Cr(II) at carbon electrodes in acidic aqueous solutions

The electrochemical synthesis of Cr(II) has been investigated on a vitreous carbon rotating disc electrode and a graphite felt electrode using cyclic voltammetry, impedance spectroscopy and chronoamperometry. The results show that in 0.1 M Cr(III) + 0.5 M sulphuric acid and in 0.1 M Cr(III) + 1 M hydrochloric acid over an electrode potential range of –0.8 to 0.8 V vs SCE, the electrochemical reaction at carbon electrodes is essentially a surface process of proton adsorption and desorption, without significant hydrogen evolution and chromium(II) formation. At electrode potentials more negative than –0.8 V vs SCE, both hydrogen evolution and chromium(II) formation occurred simultaneously. At electrode potentials –0.8 to –1.2 V vs SCE, the electrochemical reduction of Cr(III) on carbon electrodes is controlled mainly by charge transfer rather than mass transport. Measurements on vitreous carbon and graphite felt electrodes in 1 M HCl, with and without 0.1 M CrCl₃, allowed the exchange current density and Tafel slope for hydrogen evolution, and for the reduction of Cr(III) to Cr(II), to be determined. The chromium(III) reduction on vitreous carbon and graphite electrodes can be predicted by the extended high field approximation of the Butler–Volmer equation, with a term reflecting the conversion rate of Cr(III) to Cr(II).     

Anodic decomposition of citric acid on gold and stainless steel electrodes: An in situ-FTIR-spectroscopic investigation

The electrochemical decomposition of citric acid on gold and stainless steel AISI 304 (18% Cr, 10% Ni) electrodes was investigated using the technique of in situ InfraRed Reflection Absorption FTIR Spectroscopy (IRRAS) in combination with cyclic voltammetric measurements. The applied potential sweep starts from −0.265 up to +2.5 V on gold and from +0.4 up to +2.4 V on steel electrodes. The initial potentials of the anodic decomposition of citric acid could be observed on both electrode materials. Carbon dioxide was detected as decomposition product. Using stainless steel electrodes, the decarboxylation of citric acid and the forming of citrate complexes were observed. The consumption of citric acid is both due to its anodic decomposition and the generation of soluble citrate complexes of iron, nickel and chromium, resulting from the transpassive dissolution of the electrode material. At potentials more positive than +500 mV both processes are occurring simultaneously.     

Electroreduction of nitrate ions on Pt(1 1 1) electrodes modified by copper adatoms

Kinetics and mechanism of nitrate ion reduction on Pt(1 1 1) and Cu-modified Pt(1 1 1) electrodes have been studied by means of cyclic voltammetry, potentiostatic current transient technique and in situ FTIRS in solutions of perchloric and sulphuric acids to elucidate the role of the background anion. Modification of platinum surface with copper adatoms or small amount of 3D-Cu crystallites was performed using potential cycling between 0.05 and 0.3 V in solutions with low concentration of copper ions, this allowed us to vary coverage θ_Cu smoothly. Following desorption of copper during the potential sweep from 0.3 to 1.0 V allowed us to estimate actual coverage of Pt surface with Cu adatoms. Another manner of the modification was also applied: copper was electrochemically deposited at several constant potentials in solutions containing 10⁻⁵ or 10⁻⁴ M Cu²⁺ and 5 mM NaNO₃ with registration of current transients of copper deposition and nitrate reduction.It has been found that nitrate reduction at the Pt(1 1 1) surface modified by copper adatoms in sulphuric acid solutions is hindered as compared to pure platinum due to induced sulphate adsorption at E < 0.3 V. Sulphate blocks the adsorption sites on the platinum surface and/or islands of epitaxial Cu(1 × 1) monolayer thus hindering the adsorption of nitrate anions and their reduction. The extent of inhibition weakly depends on the copper adatom coverage. Deposition of a small amount of bulk copper does not affect noticeably the rate of nitrate reduction.Nitrate reduction on copper-modified Pt(1 1 1) electrodes in perchloric acid solutions occurs much faster as compared to pure platinum. The steady-state currents are higher by 4 and 2 orders of magnitude at the potentials of 0.12 and 0.3 V, respectively. The catalytic effect of copper adatoms is largely caused by the facilitation of nitrate adsorption on the platinum surface near Cu_ad and/or on the islands of the Cu(1 × 1) monolayer (induced nitrate adsorption).Hydrogen adatoms block the adsorption sites on platinum for NO₃⁻ anion adsorption and inhibit reactions of nitrate reduction even at moderate surface coverage.The products of nitrate reduction in sulphuric and perchloric acids are essentially the same (NO and ammonia) irrespective of the presence or absence of Cu on the platinum surface.     

Influence of halide anions on the behavior of pyridine adsorbed on Au(111) electrode

The effect of halide anions on pyridine-d₅ adsorbed on Au(111) electrode has been studied in neutral solutions containing F⁻, Cl⁻, and Br⁻ by IRAS and differential capacity measurement. In the NaF solution, N-bonded pyridine increases up to 0.1 V, and a new adsorbed state due to the N-bonded type grows at positive potentials. In the NaCl solution, the N-bonded type grows at all of adsorbed potential except for the appearance of the new adsorbed state at 0.2 V. In the NaBr containing solution, the new adsorbed state is not observed. In the NaCl and NaBr solutions, the total amount of the N-bonded pyridine is suppressed at positive potentials. We propose that the new band is attributed to an ordered layer of the N-bonded pyridine on the Au(111) electrode, and that the formation of the ordered layer is inhibited by the adsorption of Cl⁻ and Br⁻.     

Standard potential determinations for the magnesium and magnesium amalgam electrodes and conductance data for magnesium salts in selected aprotic solvents

Standard potentials for the magnesium and magnesium amalgam electrodes relative to the silver electrode have been determined in dimethylformamide (DMF), propylene carbonate (PC) and acetonitrile (AN) solutions at ambient temperature (295 ± 2K) from emf measurements obtained using both stationary pool and flowing amalgam electrodes. Specific and molar conductance data are also presented for MgCl₂ and Mg(ClO₄)₂ solutions in DMF, PC, AN and γ-butyrolactone (BL) at 295 K and 233 K. On the basis of the molar conductance data for PC/MgCl₂ and BL/MgCl₂ solutions, the formation of magnesium halide-bridged polymeric species is proposed.     

Cyclic voltammetry study of arsenic in acidic solutions

An electrochemical investigation of arsenic species in acidic solutions, using cyclic voltammetry at a platinum rotating disk electrode, has been carried out. A well defined peak at about 1 V_SCE, with a large overpotential (>0.5 V) is attributed to the oxidation of As(III) to As(V). The reaction is under the mixed control of ionic transport and charge transfer. The corresponding reduction of As(V) is not observed in the potential range of the study (−0.6 to +1.2 V_SCE). As(V) is not electrochemically active in this range and it has no effect on hydrogen evolution. With As(III) in solution, hydrogen evolution on Pt is shifted towards more negative potentials and it takes place simultaneously with arsine production. A small cathodic peak at −0.2 V_SCE and a corresponding anodic peak at +0.3 V_SCE are attributed to the deposition of a thin layer of As by reduction of As(III) and its dissolution.