Electrochemical incineration of chloranilic acid using Ti/IrO2, Pb/PbO2 and Si/BDD electrodes

The electrochemical oxidation of chloranilic acid (CAA) has been studied in acidic media at Pb/PbO₂, boron-doped diamond (Si/BDD) and Ti/IrO₂ electrodes by bulk electrolysis experiments under galvanostatic control. The obtained results have clearly shown that the electrode material is an important parameter for the optimization of such processes, deciding of their mechanism and of the oxidation products. It has been observed that the oxidation of CAA generates several intermediates eventually leading to its complete mineralization. Different current efficiencies were obtained at Pb/PbO₂ and BDD, depending on the applied current density in the range from 6.3 to 50 mA cm⁻². Also the effect of the temperature on Pb/PbO₂ and BDD electrodes was studied.UV spectrometric measurements were carried out at all anodic materials, with applied current density of 25 and 50 mA cm⁻². These results showed a faster CAA elimination at the BDD electrode. Finally, a mechanism for the electrochemical oxidation of CAA has been proposed according to the results obtained with the HPLC technique.     

Structure and properties of PbO2-CeO2 anodes on stainless steel

The lack of ideal anodes with excellent activity and stability is one of the critical problems in electrochemical oxidation for organic wastewater treatment. It is reported in this paper that the PbO₂-CeO₂ films electrodeposited on stainless steel were used as catalytic electrodes for treating antibiotic wastewater. The PbO₂-CeO₂ films on stainless steel were proved to be high stability, good activity and relatively low cost. Because of these properties, the films are more attractive than any other electrocatalytic materials among conventional dimensionally stable anodes (DSA). Experimental results showed that the PbO₂-CeO₂ electrode has a service life of 1100 h in 3 M H₂SO₄ solution under a current density of 1 A cm⁻² at 35 °C, compared with 300 h for PbO₂ under the same conditions. The X-ray diffraction (XRD) patterns and SEM images indicated that the PbO₂-CeO₂ films on stainless steel have a dense structure and the preferred crystalline orientation on the substrate surface was changed. Color and chemical oxygen demand (COD) of antibiotics wastewater were studied by electrolysis by using these electrodes as anode and stainless steel as cathode. The results indicated that the anodes have excellent activity in antibiotic wastewater treatment. The PbO₂-CeO₂ electrodes have high chemical stability which contributed by the superstable nature of the electrode, dense microstructure, good conductivity and the improvement of bonding with the stainless steel during electrodeposition.     

Effects of ultrasound on electrochemical oxidation mechanisms of p-substituted phenols at BDD and PbO2 anodes

The effects of low-frequency (40 kHz) ultrasound are investigated with regard to the effectiveness and mechanisms of electrochemical oxidation of p-substituted phenols (p-nitrophenol, p-hydroxybenzaldehyde, phenol, p-cresol, and p-methoxyphenol) at BDD (boron-doped diamond) and PbO₂ anodes. Although ultrasound improved the disappearance rates of p-substituted phenols at both the BDD and PbO₂ anodes, the degree of enhancement varied according to the type of p-substituted phenol and type of anode under consideration. At the BDD anode, the %Increase values were in the range 73-83% for p-substituted phenol disappearance and in the range 60-70% for COD removal. However, at the PbO₂ anode, the corresponding %Increase values were in the range 50-70% for disappearance of p-substituted phenols and only 5-25% for COD removal, much lower values than obtained at the BDD anode. Further investigations on the influence of ultrasound on the electrochemical oxidation mechanisms at BDD and PbO₂ anodes revealed that the different increase extent were due to the specialized electrochemical oxidation mechanisms at these two anodes. The hydroxyl radicals were mainly free at the BDD electrodes with a larger reaction zone, but adsorbed at the PbO₂ electrodes with a smaller reaction zone. Therefore, the enhancement due to ultrasound was greater at the BDD anode than at the PbO₂ anode.     

Electrodeposited PbO2 thin film as positive electrode in PbO2/AC hybrid capacitor

Lead dioxide (PbO₂) thin films were prepared on Ti/SnO₂ substrates by means of electrodeposition method. Galvanostatic technique was applied in PbO₂ film formation process, and the effect of deposition current on morphology and crystalline form of the PbO₂ thin films was studied by means of scanning electron microscopy (SEM) and X-ray diffraction (XRD). The energy storage capacity of the prepared PbO₂ electrode was investigated by means of cyclic voltammetry (CV) and charge/discharge cycles, and a rough surface structure PbO₂ film was selected as positive electrode in the construction of PbO₂/AC hybrid capacitor in a 1.28 g cm⁻³ H₂SO₄ solution. The electrochemical performance was determined by charge/discharge tests and electrochemical impedance spectroscopy (EIS). The results showed that the PbO₂/AC hybrid capacitor exhibited high capacitance, good cycling stability and long cycle life. In the voltage range of 1.8-0.8 V during discharge process, considering the weight of all components of the hybrid capacitor, including the two electrodes, current collectors, H₂SO₄ electrolyte and separator, the specific energy and power of the device were 11.7 Wh kg⁻¹ and 22 W kg⁻¹ at 0.75 mA cm⁻², and 7.8 Wh kg⁻¹ and 258 W kg⁻¹ at 10 mA cm⁻² discharge currents, respectively. The capacity retains 83% of its initial value after 3000 deep cycles at the 4 C rate of charge/discharge.     

Preparation and characterization of PbO2 electrodes doped with different rare earth oxides

PbO₂ electrodes doped with rare earth oxides (Re-PbO₂), including Er₂O₃, Gd₂O₃, La₂O₃ and CeO₂, were prepared by anodic codeposition in order to investigate the effect of rare earth oxide dopants on the properties of PbO₂ electrodes. The physicochemical properties of the Re-PbO₂ electrodes were analyzed by spectral methods and electrochemical measurements. The surface morphology of the Re-PbO₂ electrodes held the characteristics of the dopants and the crystal grain of PbO₂. The crystal structure of the PbO₂ electrodes was also influenced by doping with different rare earth oxides. The presence of Er₂O₃ and La₂O₃ in the PbO₂ films could enhance the direct anodic oxidation, which was helpful to mineralize 4-chlorophenol. The 4-chlorophenol decay on the Re-PbO₂ electrodes was analyzed and good fitting was found using the relation for the pseudo-first order reaction. Of the electrodes examined, the Er-PbO₂ electrode exhibited the best performance for the degradation of 4-chlorophenol. The removal rates of COD and 4-chlorophenol during the 9 h electrolysis at a current density of 20 mA cm⁻² were 80.7 and 100%, respectively, with the current efficiency being 16.0-10.1%.     

Electrocatalytic oxidation of ascorbic acid by [Fe(CN)6] redox couple electrostatically trapped in cationic N,N-dimethylaniline polymer film electropolymerized on diamond electrode

Multinegatively charged metal complex, hexacyanoferrate ([Fe(CN)₆]⁴⁻), was electrostatically trapped in the cationic polymer film of N,N-dimethylaniline (PDMA) which was electrochemically deposited on the boron-doped diamond (BDD) electrode by controlled-potential electro-oxidation of the monomer. This ferrocyanide-trapped PDMA film was used to catalyze the oxidation of ascorbic acid (AA). Increase in the oxidation current response with a negative shift of the anodic peak potential was observed at the cationic PDMA film-coated BDD (PDMA|BDD) electrode, compared with that at the bare BDD electrode. A more drastic enhancement in the oxidation peak current as well as more negative shift of oxidation potential was found at the ferrocyanide-trapped PDMA film-coated BDD ([Fe(CN)₆]^3−/4−|PDMA|BDD) electrode. This [Fe(CN)₆]^3−/4−|PDMA|BDD electrode can be used as an amperometric sensor of AA. Ferrocyanide, electrostatically trapped in the polymer film shows more electrocatalytic activity than that coordinatively attached to the polymer film or dissolved in the solution phase. The electrocatalytic current depends on the surface coverage of ferricyanide, Γ_Fe, within the polymer film. Diffusion coefficient (D) of AA in the solution was estimated by rotating disk electrode voltammetry: D = (5.8 ± 0.3) × 10⁻⁶ cm² s⁻¹. The second-order rate constant for the catalytic oxidation of AA by ferricyanide was also estimated to be 9.0 × 10⁴ M⁻¹ s⁻¹. In the hydrodynamic amperometry using the [Fe(CN)₆]^3−/4−|PDMA|BDD electrode, a successive addition of 1 μM AA caused the successive increase in current response with equal amplitude and the sensitivity was calculated as 0.233 μA cm⁻² μM⁻¹.     

On the performances of lead dioxide and boron-doped diamond electrodes in the anodic oxidation of simulated wastewater containing the Reactive Orange 16 dye

The performances of the Ti-Pt/β-PbO₂ and boron-doped diamond (BDD) electrodes in the electrooxidation of simulated wastewaters containing 85 mg L⁻¹ of the Reactive Orange 16 dye were investigated using a filter-press reactor. The electrolyses were carried out at the flow rate of 7 L min⁻¹, at different current densities (10-70 mA cm⁻²), and in the absence or presence of chloride ions (10-70 mM NaCl). In the absence of NaCl, total decolourisation of the simulated dye wastewater was attained independently of the electrode used. However, the performance of the BDD electrode was better than that of the Ti-Pt/β-PbO₂ electrode; the total decolourisations were achieved by applying only 1.0 A h L⁻¹ and 2.0 A h L⁻¹, respectively. In the presence of NaCl, with the electrogeneration of active chlorine, the times needed for total colour removal were markedly decreased; the addition of 50 mM Cl⁻ or 35 mM Cl⁻ (for Ti-Pt/β-PbO₂ or BDD, respectively) to the supporting electrolyte led to a 90% decrease of these times (at 50 mA cm⁻²). On the other hand, total mineralization of the dye in the presence of NaCl was attained only when using the BDD electrode (for 1.0 A h L⁻¹); for the Ti-Pt/β-PbO₂ electrode, a maximum mineralization of 85% was attained (for 2.0 A h L⁻¹). For total decolourisation of the simulated dye wastewater, the energy consumption per unit mass of dye oxidized was only 4.4 kWh kg⁻¹ or 1.9 kWh kg⁻¹ using the Ti-Pt/β-PbO₂ or BDD electrode, respectively. Clearly the BDD electrode proved to be the best anode for the electrooxidative degradation of the dye, either in the presence or absence of chloride ions.     

Effect of chloride concentration on the electrochemical treatment of a synthetic tannery wastewater

The electrochemical treatment of a synthetic tannery wastewater prepared with 30 compounds used in animal skin processing was studied. Electrolyses were performed in a one-compartment flow cell at a current density of 20 mA cm⁻², using a dimensionally stable anode (DSA^®) of composition Ti/Ir_0.10Sn_0.90O₂ as the working electrode. Effects of chloride concentration and presence of sulfate were evaluated. Variation in the concentration of phenolic compounds as a function of electrolysis time revealed a first-order exponential decay; faster phenol removals were obtained with increasing chloride concentration in the wastewater. Lower phenol removals were obtained in the presence of sulfate. Higher chloride concentrations led to a faster decrease in total organic carbon (TOC), chemical oxygen demand (COD), and absorbance values at 228 nm. Faster wastewater color removal, higher current efficiency and lower energy consumption were also obtained. This electrochemical treatment was also able to reduce the wastewater toxicity for Daphnia similis.     

A comparison of electrochemical degradation of phenol on boron doped diamond and lead dioxide anodes

This work compares two electrode materials used to mineralize phenol contained in waste waters. Two disks covered with either boron doped diamond (BDD) or PbO₂ were used as anodes in a one compartment flow cell under the same hydrodynamic conditions. Efficiencies of galvanostatic electrolyses are compared on the basis of measurements of Total Organic Carbon (TOC) and Chemical Oxygen Demand (COD). Galvanostatic electrolyses were monitored by analysis of phenol and of its oxidation derivatives to evaluate the operating time needed for complete elimination of toxic aromatics. The experimental current efficiency is close to the theoretical value for the BDD electrode. Other parameters being equal, phenol species disappeared at the same rate using the two electrode materials but the BDD anode showed better efficiency to eliminate TOC and COD. Moreover, during the electrolysis less intermediates are formed with BDD compared to PbO₂ whatever the current density. A comparison of energy consumption is given based on the criterion of 99% removal of aromatic compounds.     

Electrochemical removal of the insecticide imidacloprid from water on a boron-doped diamond and Ta/PbO<Subscript>2</Subscript> anodes using anodic oxidation process

The removal of pesticides from water is a major environmental concern. This study investigates the electrochemical removal of the insecticide imidacloprid (IMD) from aqueous solutions on a boron-doped diamond (BDD) and Ta/PbO₂ anodes under galvanostatic electrolysis. The influence of operating parameters, such as applied current density (50–100 mA cm^?2), initial chemical oxygen demand COD (0) (281–953 mg L^?1), temperature (25–65 °C) and pH (3.0–10.0) on COD and instantaneous current efficiency (ICE), was studied using the BDD electrode. The degradation efficiency of IMD increased by increasing current density and temperature, but noticeably decreased by the increase of initial pH value and initial concentration of IMD. The COD decay follows a pseudo-first-order kinetic, and the process was under mass transport control. COD removal reaches 90% when using an apparent current density of 100 mA cm^?2, initial COD of 953 mg L^?1, pH of 3.0 and at 25 °C after 4.5 h electrolysis time. Compared with Ta/PbO₂, BDD anode has shown better performance and rapidity in the COD removal using the same electrolysis device.     

Oxygen transport in composite mediated biocathodes

A numerical simulation of an enzyme-catalyzed oxygen cathode is presented and applied to the analysis of transport limitations in operating electrodes, with the goal of predicting the limits of obtainable cathode current density. Based on macrohomogeneous and thin-film theories, and accounting for dual-substrate enzyme kinetics, the one-dimensional model predicts a maximum current density of about 9.2 mA cm⁻² at 0.6 V (SHE) for a 300 μm thick electrode operating oxygen-saturated pH 5 buffer at 37 °C and relying on diffusion of dissolved oxygen alone. However, by introducing gas-phase diffusive transport, or alternatively a convective, flow-through approach, the model predicts that electrodes of identical thickness may provide current densities up to 60 mA cm⁻² in air and exceeding 100 mA cm⁻² in pure O₂. Such performance would move enzyme electrodes closer to practical implementation in implantable power devices and other low-temperature fuel cells such as direct methanol fuel cells.     

Study of the electrochemical hydrogen storage properties of the proton-conductive perovskite-type oxide LaCrO3 as negative electrode for Ni/MH batteries

LaCrO₃ was prepared by glycine combustion method and investigated as negative electrode for Ni/MH batteries. The structures of the as-calcined powder and the 20th charge-discharge cycle sample were characterized by XRD. The electrochemical experimental results demonstrated that the LaCrO₃ electrode showed excellent electrochemical reversibility and considerably high charge-discharge capacity at various temperatures. Except for the charge-discharge cycle at 298 K, the discharge capacities of LaCrO₃ electrode keep steady at 107.1 mA h g⁻¹and 285 mA h g⁻¹ at 313 K and 333 K after 5 cycles, respectively.     

Effect of synthesis condition on the structural and electrochemical properties of Li[Ni1/3Mn1/3Co1/3]O2 prepared by the metal acetates decomposition method

In order to get homogeneous layered oxide Li[Ni_1/3Mn_1/3Co_1/3]O₂ as a lithium insertion positive electrode material, we applied the metal acetates decomposition method. The oxide compounds were calcined at various temperatures, which results in greater difference in morphological (shape, particle size and specific surface area) and the electrochemical (first charge profile, reversible capacity and rate capability) differences. The Li[Ni_1/3Mn_1/3Co_1/3]O₂ powders were characterized by means of X-ray diffraction (XRD), charge/discharge cycling, cyclic voltammetry and SEM. XRD experiment revealed that the layered Li[Ni_1/3Mn_1/3Co_1/3]O₂ material can be best synthesized at temperature of 800 °C. In that synthesized temperature, the sample showed high discharge capacity of 190 mAh g⁻¹ as well as stable cycling performance at a current density of 0.2 mA cm⁻² in the voltage range 2.3-4.6 V. The reversible capacity after 100 cycles is more than 190 mAh g⁻¹ at room temperature.     

An electrochemical methanol sensor based on a Pd-Ni/SiNWs catalytic electrode

A novel electrochemical methanol sensor based on a catalytic electrode of palladium-nickel/silicon nanowires (Pd-Ni/SiNWs) is presented in this paper. Scanning electron microscopy (SEM), energy-dispersive X-ray spectroscopy (EDS), and electrochemical methods are employed to investigate the Pd-Ni/SiNWs electrode materials. These nanocomposite materials exhibit a highly ordered, wire-like structure with a wire length of ∼50 μm and a wire diameter ranging from 100 to 300 nm. The substrate has good electrocatalytic activity towards the oxidation of methanol in alkaline solutions. The performances of the prototype sensor are characterized by cyclic voltammetry and fixed potential amperometry techniques. In a 1 mol L⁻¹ KOH solution containing different methanol concentrations, the sensor exhibits a good sensitivity of 1.96 mA mmol⁻¹ L cm⁻² with R² = 0.99 and the corresponding detection limit of 18 μmol L⁻¹ (signal-to-noise ratio = 3, S/N = 3) for cyclic voltammetry. Meanwhile, the electrode also displays a sensitivity of 0.48 mA mmol⁻¹ L cm⁻² with R² = 0.98 and the corresponding detection limit of 25 μmol L⁻¹ (S/N = 3) for a fixed potential amperometry at −0.3 V versus an Ag/AgCl reference electrode. The results demonstrate that the Pd-Ni/SiNWs catalytic electrode has potential as an efficient and integrated sensor for methanol detection.     

Evaluation of the photoelectrocatalytic method for oxidizing chloride and simultaneous removal of microcystin toxins in surface waters

The production of chlorine was investigated in the photoelectrocatalytic oxidation of a chloride-containing solution using a TiO₂ thin-film electrode biased at current density from 5 to 50 mA cm⁻² and illuminated by UV light. Such parameters as chloride concentrations from 0.001 to 0.10 mol L⁻¹, pH 2-12, and interfering salts were varied in this study in order to determine their effect on this oxidation process. At an optimum condition this photoelectrocatalytic method can produce active chlorine at levels compatible to water disinfections processes using a chloride concentration higher than 0.010 mol L⁻¹ at a pH of 4 and a current density of 30 mA cm⁻². The method was successfully applied to treat surface water collected from a Brazilian river. After 150 min of photoelectrocatalytic oxidation, we obtained a 90% reduction in total organic carbon removal, a 100% removal of turbidity, a 93% decrease in colour and a chemical oxygen demand (COD) removal of around 96% (N = 3). The proposed technology based on photoelectrocatalytic oxidation was also tested in treating 250 mL of a solution containing 0.05 mol L⁻¹ NaCl and 50 μg L⁻¹ of Microcystin aeruginosa. The bacteria is completely removed after 5 min of photoelectrocatalysis following an initial rate constant removal of −0.260 min⁻¹, suggesting that the present method could be considered as a promising alternative to chlorine-based disinfections.     

Iron-enriched natural zeolite modified carbon paste electrode for H2O2 detection

This work demonstrates that iron-enriched natural zeolitic volcanic tuff (Paglisa deposit, Cluj county, Transilvania, Romania) resulting from a previous use as adsorbent in wastewater treatment can be recycled into effective electrode modifier applied to the electrocatalytic detection of hydrogen peroxide. After physico-chemical characterization of tuff samples using various techniques such as chemical analysis, X-ray diffraction, scanning electron microscopy, infrared spectroscopy, BET analysis and X-ray photoelectron spectroscopy, the electrochemical response of the iron-enriched zeolites was studied on the basis of solid carbon paste electrodes modified with these samples. The results indicate that iron centers in the zeolite are electroactive and that they act as electrocatalysts in the voltammetric and amperometric detection of H₂O₂. Best performance was achieved in phosphate buffer at pH 7, showing a sensitivity of 0.57 mA M⁻¹ cm⁻², a detection limit down to 60 μM, and a linear domain up to 100 mM H₂O₂.     

Electrochemical incineration of chloromethylphenoxy herbicides in acid medium by anodic oxidation with boron-doped diamond electrode

The electrochemical degradation of saturated solutions of herbicides 4-chloro-2-methylphenoxyacetic acid, 2-(4-chlorophenoxy)-2-methylpropionic acid and 2-(4-chloro-2-methylphenoxy)propionic acid in 1 M HClO₄ on a boron-doped diamond (BDD) thin film anode has been studied by chronoamperometry, cyclic voltammetry and bulk electrolysis. At low anodic potentials polymeric products are formed causing the fouling and deactivation of BDD. This is reactivated at high potentials when water decomposes producing hydroxyl radical as strong oxidant of organics. Electrolyses in a batch recirculation system at constant current density ≥8 mA cm⁻² yielded overall decontamination of all saturated solution. The effect of current density and herbicide concentration on the degradation rate of each compound, the specific charge required for its total mineralization and instantaneous current efficiency have been investigated. Experimental results have been compared with those predicted by a theoretical model based on a fast anodic oxidation of initial herbicides, showing that at 30 mA cm⁻² their degradation processes are completely controlled by mass transfer. Kinetic analysis of the change of herbicide concentration with time during electrolysis, determined by high-performance liquid chromatography, revealed that all compounds follow a pseudo first-order reaction. Aromatic intermediates and generated carboxylic acids have been identified using this technique and a general pathway for the electrochemical incineration of all herbicides on BDD is proposed.     

Platinum-modified titanium anodes for the electrolytic destruction of nitric acid

Three sets of electrodes, namely Pt electroplated Ti (PET) and diffusion annealed PET (DAPET) of plating thickness 3, 5, 7 and 10 μm and thermochemically glazed mixed oxide coated titanium anode (MOCTA-G) were evaluated for their performance, with a view to optimizing the current density conditions for maximum efficiency during the electrolytic destruction of nitric acid. In the acid killing by electro-reduction process, concentration of nitric acid in the high level waste (HLW) from the spent nuclear fuel reprocessing plant was brought down from about 4 to 0.5 M in order to reduce the amount of HLW by subsequent evaporation and to minimise the corrosion in waste tanks during storage of the concentrated waste solution. The electrochemical reduction of 4 and 8 M nitric acid to near neutral conditions was carried out with the above-said anodes and Ti cathode at various cathodic current densities ranging from 10 to 80 mA cm⁻². At current densities below 15 mA cm⁻² MOCTA-G electrode worked satisfactorily, whereas PET and DAPET electrodes could withstand and function well at much higher cathodic current densities (up to 80 mA cm⁻²). The life assessment of a 3 μm thick PET electrode at a cathodic current density of 60 mA cm⁻² in 8 M HNO₃ for a period of 110 h showed no failure. Phase identification of the plated electrodes was done by XRD measurements and their surface morphology was investigated by SEM.     

A novel micro-spherical CoSn2/Sn alloy composite as high capacity anode materials for Li-ion rechargeable batteries

Micro-scaled spherical CoSn₂/Sn alloy powders synthesized from oxides of Sn and Co via carbothermal reduction at 800 °C were examined for use as anode materials in Li-ion battery. The phase composition and particle morphology of the CoSn₂/Sn alloy composite powders were investigated by XRD, SEM and TEM. The prepared CoSn₂/Sn alloy composite electrode exhibits a low initial irreversible capacity of ca. 140 mAh g⁻¹, a high specific capacity of ca. 600 mAh g⁻¹ at constant current density of 50 mA g⁻¹, and a good rate capability. The stable discharge capacities of 500-515 mAh g⁻¹ and the columbic efficiencies of 95.8-98.1% were obtained at current density of 500 mA g⁻¹. The relatively large particle size of CoSn₂/Sn alloy composite powder is apparently favorable for the lowering of initial capacity loss of electrode, while the loose particle structural characteristic and the Co addition in Sn matrix should be responsible for the improvement of cycling stability of CoSn₂/Sn electrode.     

Studies on the electrochemical behavior of 3-nitrobenzaldehyde thiosemicarbazone at glass carbon electrode modified with nano-γ-Al2O3

Nano-γ-Al₂O₃ is dispersed onto the glass carbon electrode (GCE) by polishing. This nanostructured modified GCE exhibits a great enhancement to the redox responses of 3-nitrobenzaldehyde thiosemicarbazone (3-NBT). In comparison with bare GCE, 3-NBT gives a more sensitive voltammetric response because of the nanoparticle’s unique properties. The lowest detectable concentration (3σ) of 3-NBT is estimated to be 1.18 × 10⁻⁶ M (accumulation for 4 min). The linear relationship between peak current and concentration of 3-NBT holds in the range 1.0 × 10⁻⁵ M to 1.0 × 10⁻⁴ M (r = 0.9981). The electrochemical properties of 3-NBT on this modified electrode have been investigated with various electrochemical methods. The results indicate that the transference of one electron and one proton involves electrode radical reaction processes I and II, respectively. The coverage value (Γ) of 1.62 × 10⁻⁹ mol cm⁻² was calculated and the electrochemical parameters, diffusion coefficient D (2.54 × 10⁻³ cm² s⁻¹, 2.03 × 10⁻³ cm² s⁻¹) and reaction rate constant k_s (5.9573 s⁻¹, 7.15 × 10⁻² cm s⁻¹) were obtained for quasi-reversible system I and irreversible system II, respectively.