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.     

A wall jet electrode reactor and its application to the study of electrode reaction mechanisms Part II: A general computational method for the mass transport problems involved

A numerical computational method to solve the problems of mass transport to the impinged surface of a wall-jet electrode reactor is put forward, thus providing the necessary tool for a quantitative electrochemical investigation of the mechanism of electrode processes, using a wall-jet electrode reactor as a hydrodynamic electrode system. The computational method is based on a second order-correct implicit finite difference approach and a coordinate transformation making a simple Cartesian space discretization compatible with efficient computing, thus allowing the computations to be performed on a personal computer. The computational approach is demonstrated through calculation of a single step chronoamperometric transient for a simple one electron transfer reaction and shown to be accurate by comparing the computed with experimentally determined current transients using as a model reaction the reduction of ferricyanide ions at a platinum electrode surface from a 0.01 m K₃Fe(CN)6-0.01 m K₄Fe(CN)₆ solution containing l m KCl as supporting electrolyteList of symbols a nozzle diameter (m) - C _i concentration of electroactive species i (mol m^–3) - C _i normalized concentration of electroactive species i - D _i diffusion coefficient of the electroactive species i (m² s^–1) - E electrode potential (V vs SCE) - E ₀ equilibrium potential (V vs SCE) - F Faraday's constant (C mol^–1) - dimensionless parameter, describing the distance normal to the impinged electrode - H distance between the working electrode and the tip of the nozzle (m) - I electrode current (A) - k _r constant linking the typical velocity of the wall-jet to the mean velocity in the nozzle - M flux of exterior momentum flux - v kinematic viscosity (m² s^–1) - r distance along the impinged electrode in cylindrical pole coordinates having their origin at the intersection of the jet axis and the electrode surface - R radius of the impinged electrode (m) - dimensionless time - t time (s) - v _I velocity component along the impinged electrode (m s^–1) - v _Z velocity component normal to the impinged electrode (m s^–1) - V _f volume flow rate (m^–3 s^–1) - dimensionless parameter, describing the distance normal to the impinged electrode - z distance normal to the impinged electrode in cylindrical pole coordinates having their origin at the intersection of the jet axis and the electrode surface (m)     

The electrodeposition of gallium from synthetic Bayer-process liquors

Gallium was electrodeposited from a synthetic Bayer solution comprising 4.5m NaOH/0.2m Na₂CO₃/0.3m NaCl/1.7m Al(OH)₃. Hydrogen evolution occurred in parallel with gallium deposition, the latter process being in part controlled by mass transfer and in part by the electron transfer step. Combined coulometric and voltammetric measurements allowed estimation of a diffusion coefficient for Ga (III) of 3.6×10^–6 cm² sec^–1 at 40° C. The coulombic efficiency for gallium deposition was a function of current density, deposition time, electrode rotation rate, temperature and gallium concentration. Values of up to 11% were obtained on a copper electrode from a solution containing 3.2×10^–3 m Ga (III). Heavy-metal impurities, such as iron and vanadium, usually found in these liquors, promote the hydrogen evolution reaction, completely inhibiting gallium production if present above certain critical concentrations.     

Oxidation of arsenopyrite (FeAsS) in acid Part II: Stoichiometry and reaction scheme

The electrochemical oxidation of arsenopyrite (FeAsS) in 0.01 iv1 chloride solution at pH 2 has been investigated and the effect of electrode potential, temperature and arsenopyrite mineral composition on the reaction stoichiometry studied. Iron, arsenic and sulfur products were formed in the ratio 1 : 1 : 1, for all conditions for arsenic deficient and stoichiometric arsenopyrite. Product speciation was dependent on temperature and potential, but not on arsenopyrite composition. At 25°C, Fe(ii), Fe(iii), As(iii), As(v), S, SO ₄ ^2– and S(x) (which could be a polythionate such as tetrathionate or pentathionate) were formed and 9e^– produced per mol of arsenopyrite oxidized. At 75°C, practically no S(x) was formed and 7.5 e^– produced per mol of arsenopyrite oxidized. A qualitative reaction scheme, based on the decomposition of thiosulfate to polythionate in the presence of As(iii), is outlined.     

Selective oxidation of pentachlorophenol on diamond electrodes

The influence of electrode potential on pentachlorophenol (PCP) oxidation on boron doped diamond (BDD) electrodes in a 0.1 mol L^–1 Britton–Robinson buffer (pH 5.5) is described. Controlled potential electrolyses were carried at 0.9, 2.0 and 3.0 V vs Ag/AgCl and the solutions analysed by square wave voltammetry, high performance liquid chromatography, chloride ion selective electrode and spectroscopy in the ultraviolet–visible region. At low positive potential (0.9 V), the formation of an adherent film on the electrode surface involving the transference of 1 electron per PCP molecule was observed. The film was identified as the dimer 2,3,4,5,6-pentachloro-4-pentachlorophenoxy-2,5-cyclohexadienone and the current efficiency was as high as 90%. At potentials close to the onset of O₂ evolution (2.0 V), the formation of the corresponding quinone (p-tetrachlorobenzoquinone) was detected at the beginning of the process. This was followed by further oxidation to the hydroxy-benzoquinone with a practically quantitative yield. Electrolyses carried out well into the region of oxygen evolution (3.0 V) lead to the electrochemical combustion of PCP to CO₂ and H₂O as well as to the release into solution of 5 Cl^– ions per PCP molecule destroyed.     

Redox chemistry of H2S oxidation by the British Gas Stretford process part IV: V-S-H2O thermodynamics and aqueous vanadium (v) reduction in alkaline solutions

The thermodynamics of V-H₂O and V-S-H₂O systems at 298 K are summarized in the form of potential-pH and activity-pH diagrams calculated from recently published critically assessed standard Gibbs energies of formation. At pH 9, as used in Stretford Processes, V-H₂O potential-pH diagrams predicted that the V(v)/V(iv) couple involves HV₂O₇ ^3–/V₄O₉ ^2– ions. However, in neutral and alkaline solutions there is difficulty in discriminating between kinetic intermediates and thermodynamically stable solution species, some with V(v)/V(iv) mixed oxidation states. Hence, V₁₈O₄₂ ^12– ions may be the stable V(iv) species, depending on the concentration, though no thermodynamic data are available to enable them to be included in potential-pH calculations. Potential-pH diagrams for V-S-H₂O systems predicted an area of stability for VS₄ in the pH range 2–8 and over a restricted potential range; neither VS nor VS₂ were predicted to be stable under any conditions considered. In cyclic voltammetric experiments at Hg, Au and vitreous carbon electrodes, reduction of vanadium (v) species (probably HV₂O₇ ^3– ions) was found to be irreversible on a variety of electrode surfaces and, at lower potentials, led predominantly to the formation of solid oxide films (V₃O₅, V₂O₃ and VO) rather than to V(iv) solution species, of which V₁₈O₄₂ ^12– ions probably predominate at equilibrium. In the presence of the large excess of HS^– ions required to form VS₄ ^3– ions, the electrochemical behaviour of a gold electrode was dominated by the former species.     

Mechanistic and kinetic aspects of silver dissolution in cyanide solutions

The factors influencing the dissolution kinetics of pure silver in cyanide solution have been analysed in terms of an electrochemical mechanism. A kinetic model is presented which incorporates coupled diffusion and charge transfer for the anodic branch, and combined diffusion, adsorption and charge transfer for the cathodic branch. The anodic oxidation of silver has been investigated using a silver rotating-disc electrode for concentrations between 10^–3 and 10^–1 m NaCN. Oxygen reduction on silver has been studied at oxygen partial pressures between 0.104 and 1.00 atm. Mechanistic aspects of the oxygen discharge reaction are considered in explaining the kinetic differences between gold and silver dissolution in cyanide solution. It is shown that under conditions typical of conventional cyanidation gold dissolves measurably faster than silver.     

Electrochemical behavior of pyrite in sulfuric acid solutions containing silver ions

A systematic electrochemical study of pyrite in H₂SO₄ solutions containing dissolved silver was undertaken to gain more information about the transfer of silver ions to pyrite and their role in enhancing the direct oxidation of pyrite. The results of cyclic voltammetry experiments provide additional evidence of the formation of metallic silver on the FeS₂ surface under open-circuit conditions. A pyrite electrode held at the open-circuit potential for 2 h in the presence of 10^–3 m Ag⁺ exhibits a large and sharp anodic peak at about 0.7V. The current associated with this peak is the result of the dissolution of metallic silver deposited during the initial conditioning period. There is no evidence of silver deposition without preconditioning until the potential drops below about 0.6V for Ag⁺ concentrations ranging from 10^–4 to 10^–2 m. However, subsequent silver deposition appears to be very sensitive to the dissolved silver concentration in this range. There is also evidence that the state of the pyrite surface has a pronounced influence on its interaction with silver ions. Agitation has also been found to have a significant effect on the electrochemistry of the Ag–FeS₂ system.     

Determination of overall mass transport coefficients in gas diffusion electrodes

Gas diffusion electrodes are used for many purposes, for example in fuel cells, in synthesis and as anodes in electrodeposition processes. The behaviour of gas diffusion electrodes has been the subject of many studies. In this work the transport of gas in the gas diffusion electrode, characterized by the overall mass transport coefficient, has been investigated using hydrogen-nitrogen mixtures. A reactor model for the gas compartment of the gas diffusion electrode test cell is proposed to calculate the concentration of hydrogen in the gas compartment as a function of the input concentration of hydrogen and the total volumetric gas flow rate. The mass transport coefficient is found to be independent of variations in hydrogen concentration and volumetric gas flow rate. The temperature dependence of the mass transport coefficient has been determined. A maximum was found at 40°C.Notation Agd geometric electrode surface area (m²) - C _in concentration of reactive component at the inlet of the gas compartment (mol m^–3) - c _out concentration of reactive component at the outlet of the gas compartment (mol m^–3) - E potential (V) - E _e equilibrium potential (V) - E _t upper limit potential (V) - F _v volumetric flow rate (m^–3 s^–1) - F _v,H volumetric flow rate of hydrogen (m^–3 s^–1) - F _v,N volumetric flow rate of nitrogen (m^–3 s^–1) - F _vin volumetric flow rate at the inlet of the gas compartment (m^–3 s^–1) - F _v,out volumetric flow rate at the outlet of the gas compartment (in ^–3 s^–1) - F _v,reaction volumetric flow rate of reactive component into the gas diffusion electrode (m^–3 s^–1) - Faraday constant (A s mo^–1) - I _gd current for gas diffusion electrode (A) - i _gd current density for gas diffusion electrode (A m^–2) - I _gd,1 diffusion limited current for gas diffusion electrode (A) - i _gd,1 diffusion limited current density for gas diffusion electrode (A m^–2) - I _gd,1,calc calculated diffusion limited current for gas diffusion electrode (A) - i _gd,1,calc calculated diffusion limited current density for gas diffusion electrode (A m^–2) - I _hp current for hydrogen production (A) - k _s mass transport coefficient calculated from c _out (m s^–1) - n number of electrons involved in electrode reaction - T temperature (°C) - V _m molar volume of gas (m³ mol^–1) - overpotential (V)     

Oxygen reduction on stainless steel

Oxygen reduction was studied on AISI 304 stainless steel in 0.51 m NaCl solution at pH values ranging from 4 to 10. A rotating disc electrode was employed. It was found that oxygen reduction is under mixed activation-diffusion control. The reaction order with respect to oxygen was found to be one. The values of the Tafel slope depend on the potential scan direction and pH of the solution, and range from – 115 to – 180 mV dec^–1. The apparent number of electrons exchanged was calculated to be four, indicating the absence of H₂O₂ formation.Nomenclature B =0.62 nFcD ^2/3 –^1/6 - c bulk concentration of dissolved oxygen (mol dm^–3) - D molecular diffusion coefficient of oxygen (cm² s^–1) - E electrode potential (V) - EH standard electrode potential (V) - E _H ⁰ Faraday constant (96 500 As mol^–1) - I current (A) - j current density (A cm^–2) - j _k kinetic current density (A cm^–2) - j _L limiting current density (A cm^–2) - m reaction order with respect to dissolved oxygen molecule - M molar mass (g mol^–1) - n number of transferred electrons per molecule oxygen - density (g cm^–3) - kinematic viscosity (cm² s^–1) - angular velocity (s^–1)     

Electrochemical study of the Eu(III)/Eu(II) system in molten fluoride media

The electrochemical behaviour of the Eu(III)/Eu(II) system was examined in the molten eutectic LiF–CaF₂ on a molybdenum electrode, using cyclic voltammetry, square wave voltammetry and chronopotentiometry. It was observed that EuF₃ is partly reduced into EuF₂ at the operating temperatures (1073–1143 K). The electrochemical study allowed to calculate both the equilibrium constant and the formal standard potential of the Eu(III)/Eu(II) system. The reaction is limited by the diffusion of the species in the solution; their diffusion coefficients were calculated at different temperatures and the values obey Arrhenius’ law. The second system Eu(II)/Eu takes place out of the electrochemical window on an inert molybdenum electrode, which inhibits the extraction of Eu species from the salt on such a substrate.     

Electrocatalytic behaviour of a poly(N-methylaniline) filmed electrode to hydroquinone

Poly(N-methylaniline) (PNMA) was prepared on a bare platinum electrode by electrooxidation of N-methylaniline in 1.0 mol dm^–3 HCl. The PNMA film was more stable to anodic treatment than the polyaniline film. The electric conductivity of the PNMA film was potential dependent. High conductivity appeared only within the potential region where PNMA itself was redox-active. The PNMA filmed electrode showed redox response to dissolved hydroquinone whose redox current was evident within the potential region. Furthermore, the PNMA film behaved as an electrocatalyst for the electrode reaction of hydroquinone. The kinetics of the electrocatalytic reaction were investigated mainly using a rotating disc electrode. The experimental results obtained were analysed by the theory of Albery and Hillman, and the rate constant of the electron cross-exchange transfer between hydroquinone and the redox-active sites in the film (k) was determined and found to be 6.4 × 10³ m ^–1 s^–1 at 20° C.     

Anodic Oxidation of Nitric Oxide on Au/Nafion®: Kinetics and Mass Transfer

The rate determining step for the anodic oxidation of nitric oxide on Au/Nafion^® was experimentally and theoretically found to beNO + Au Au–NO_ads The anodic oxidation of nitric oxide was first order with respect to nitric oxide. The reaction rate constant increased from 3.3×10^–5 to 9.6×10^–5cm s^–1 as the applied potential increased from 0.74 to 0.77V. The anodic oxidation of nitric oxide was controlled by the electrochemical kinetics when the anodic potential was less than 0.8 V. When the potential was greater than 1.0 V, it was located in the mass transfer region. The limiting current increased from 1184 to 1589A with increase in gas flow rate from 250 to 750ml min^–1 when the potential was set at 1.05 V and the concentration of nitric oxide was 100 ppm. The diffusion resistance in the gas diffusion layer can be neglected for gas flow rates greater than 750 ml min^–1. The diffusivity of nitric oxide and the equivalent diffusion layer thickness within the porous electrode were evaluated to be 3.43×10^–4cm²s^–1 and 0.051 cm, respectively.     

A kinetic study of the electrocatalytic oxidation of reduced glutathione at Prussian blue film-modified electrode using rotating-disc electrode voltammetry

In this work a thorough study of the oxidation of reduced glutathione (GSH) by electro-generated Berlin Green (BG) at Prussian blue (PB) film-modified glassy carbon electrode (GCE) was attempted by employing cyclic voltammetry (CV) and rotating-disc electrode (RDE) techniques. It has been shown that oxidation of GSH occurs at the potential coinciding with that of Fe^II(CN)₆ to Fe^III(CN)₆ transformation in the PB film, where no oxidation signal is observed at a bare GCE. The kinetics of catalytic reaction was investigated using a rotating-disc electrode voltammetry. The results obtained for various thicknesses of film and GSH concentrations are explained using the theory of electrocatalytic reactions at chemically modified electrodes (Andrieux–Saveant model) and it was concluded that the reaction has a “surface” reaction mechanism in which a few monolayers at film/solution side engaged in the catalytic process. However, the “surface” reaction tends to a saturation limit with increasing GSH concentration was observed and the behavior has been explained by using Michealis–Menten inner sphere kinetics. Tafel plots for various concentrations of GSH have been drawn and the slope values of 95–110 mV/decade indicate that the first electron transfer is not rate limiting process. The reaction order with respect to GSH and H⁺ were calculated as 0.6 and −0.4, respectively.     

Anodic oxidation of copper cyanide on graphite anodes in alkaline solution

The anodic oxidation of copper cyanide has been studied using a graphite rotating disc with reference to cyanide concentration (0.05–4.00 M), CN:Cu mole ratio (3–12), temperature (25–60 °C) and hydroxide concentration (0.01–0.25 M). Copper had a significant catalytic effect on cyanide oxidation. In the low polarization region (about 0.4 V vs SCE or less), cuprous cyanide is oxidized to cupric cyanide complexes which further react to form cyanate. At a CN:Cu ratio of 3 and [OH^–] = 0.25 M, the Tafel slope was about 0.12 V decade^–1. Cu(CN)₃ ^2– was discharged on the electrode and the reaction order with respect to the predicted concentration of Cu(CN)₃ ^2– is one. With increasing CN:Cu mole ratio and decreasing pH, the dominant discharged species shifted to Cu(CN)₄ ^3–. Under these conditions, two Tafel slopes were observed with the first one being 0.060 V decade^–1 and the second one 0.17–0.20 V decade^–1. In the high polarization region (about 0.4 V vs SCE or more), cuprous cyanide complexes were oxidized to copper oxide and cyanate. Possible reaction mechanism was discussed.     

Current efficiency during anodic dissolution of iron to ferrate(vi) in concentrated alkali hydroxide solutions

The dependence of the current efficiency for oxidation of an iron anode to ferrate(vi) ions in 14m NaOH was measured in the region of free convection. The highest current yield of 40% was obtained at a current density of 2.1 mA cm^–2 and temperature of 30°C. The iron anode was activated by cathodic prepolarization. The iron concentration in low oxidation states in solution was determined as 0.13 ± 0.1 and 0.29 ± 0.25 g Fe dm^–3 at 20 and 30°C, respectively. The steady state anodic polarization curves of iron in the transpassive potential region are shifted to lower potential values with increasing NaOH concentration from 11 to 171 m. At 40°C all the curves show a limiting current density around 660 mV vs Hg/HgO, namely 9 and 23 mA cm^–2 at NaOH concentrations of 11 and 17 m, respectively.     

A reaction model for the electrochemical production of p-anisidine

The work examines the possibility of a simple reaction model describing a complex organic electrosynthesis, such as the formation of p-anisidine. The experimental results obey the linear relationships of the model and in consequence the kinetic constants obtained in this way define reaction behaviour. The paper demonstrates how such a model can play a useful role in the design of pilot plant experimentation. Results from a parallel plate cell fit prediction from the model.Nomenclature [X] Concentration of species X (kmol m^–3) - b Slope of Tafel plot (mV^–1) - E Electrode potential (mV) - F Faraday (C g-equiv^–1) - F Faraday based on k-equiv = 10³F (C k-equiv^–1) - i _A Partial current density for the primary reaction (A m^–2) - i _B Partial current density for the consecutive secondary reaction (A m^–2) - i _H Partial current density for the parallel secondary reaction (A m^–2) - i Total current density=i _A+i _B+i _H (A m^–2) - k Reaction rate constant (A m^–2 per kmolm^–3) - k _H Rate constant for the parallel secondary electrode reaction (A m^–2) - k _I Individual mass transfer coefficient (m s^–1) - N Flux (kmol m^–2 s^–1) - r Reaction rate (kmol m^–2 s^–1) Sufixes A Appertaining to primary electrode reaction or species A - B Appertaining to consecutive secondary electrode reaction or species B - b In the bulk of the electrolyte - H Parallel secondary electrode reaction - s Near the electrode surface     

Physicochemical and electrocatalytic properties of LaNiO3 prepared by a low-temperature route for anode application in alkaline water electrolysis

LaNi_1–x Fe_xO₃ (x = 0, 0.25, 0.5) has been synthesized by the hydroxide solid solution precursor method for electrochemical characterization as oxygen anode in strongly alkaline medium. Studies were made at the oxide film, which was obtained by the oxide-slurry painting technique. The cyclic voltammetric study showed the formation of a diffusion-controlled quasireversible redox couple, Ni(ii)/Ni(iii), (E ⁰ - 430 ± 10 mV) at the oxide surface in 1 m KOH. The reaction was observed to follow approximately first-order kinetics in OH^– concentration. Values of the Tafel slope ranged between 59 and 86 mV decade^–1 with all the oxide film electrodes. The electrocatalytic activity was found to be greatest with the Ni/LaNi_0.75Fe_0.25O₃ electrode. A comparison was made between the electrocatalytic activities of LaNiO₃ prepared by the hydroxide solid solution precursor and by the hydroxide coprecipitation technique.     

A wall-jet electrode reactor and its application to the study of electrode reaction mechanisms Part I: Design and construction

A wall jet electrode reactor possessing a laminar flow regime, suitable for mechanistic studies, is reported. This reactor is different from those described in the literature in the size of its working electrode surface area. The reactor is evaluated by means of mass transport-limited current measurements using as a model reaction the reduction of ferricyanide ions at a platinum electrode surface from a 0.01 m K₃Fe(CN)₆-0.01 m K₄Fe(CN)₆ solution containing 1 m KCl as supporting electrolyte. The dependence of the mass transport-limited current on the crucial reactor parameters — the volume flow rate V _f (m³ s^–1), the nozzle diameter a (m) and the radius of the working electrode R (m) — is established and verified by theoretical predictions. The reactor is shown to have the desired wall jet hydrodynamics for: 1.6 × 10^–6 V _f 4.3 × 10^–6 m³ s^–1, 1.5 × 10^–3 a 3 × 10^–3 m and 1.5 × 10^–2 R 2 × 10^–2 m.List of symbols a nozzle diameter (m) - C _A concentration of A in the bulk (mol m^–3) - D _A diffusion coefficient of A (m² s^–1) - F Faraday's constant (C mol^–1) - dynamic viscosity (gm^–1 s^–1) - H distance between the working electrode and the tip of the nozzle (m) - I _lim mass-transport-limited current (A) - k _r constant linking the typical velocity of the wall-jet to the mean velocity in the nozzle - v kinematic viscosity (m² s^–1) - n number of electrons exchanged - density (g m^–3) - R radius of the working electrode (m) - t time (s) - V _f volume flow rate (m^–3 s^–1)     

Electrooxidation of Aqueous p-Methoxyphenol on Lead Oxide Electrodes

Oxidation of p-methoxyphenol (pmp) in aqueous solution on bismuth-doped lead oxide was studied, and the effects of the initial pmp concentration, applied potential and hydrodynamic conditions upon the oxidation rate were identified. Under all conditions studied, the concentration decay of pmp during electrooxidation follows first—order reaction kinetics. Through analysis of rotating ring-disc currents, the faradaic efficiencies for oxidation at various concentrations of pmp in solution were determined. Using u.v.—vis. and H¹RMN spectroscopy for solution analysis, it is shown that partial oxidation of pmp occurs in chloride-free aqueous solutions. The principal products were p-benzoquinone and maleic acid, with low production of CO₂ up to 1000 C dm^–3 charge. Mineralization to CO₂ was considerably improved upon addition of chloride ions to the solution. In situ FTIR spectra of the electrode surface during electrolysis indicated that the presence of chloride ions enhances the mineralization of pmp by reaction of benzoquinone with anodically generated hypochlorite.