Showing papers in "Journal of Applied Electrochemistry in 2010"

Reverse electrodialysis: evaluation of suitable electrode systems

Abstract: Reverse electrodialysis (RED) is a method for directly extracting electrical energy from salinity gradients, especially from sea and river water. For the commercial implementation of RED, the electrode system is a key component. In this paper, novel electrode systems for RED were compared with existing systems on safety, health, environment, technical feasibility and economics. Systems with inert DSA-type electrodes and a NaCl–HCl supporting electrolyte with the reversible Fe2+/Fe3+ redox couple or the [Fe(CN)6]4–/Fe(CN)6]3– couple achieved the highest ranking. Improvements of the electrode system are also discussed like the use of special stable metal electrodes, graphite electrodes, other reversible redox couples, capacitive electrodes and electrolytes with carbon particles.

Mathematical modeling of high-pressure PEM water electrolysis

Abstract: This paper is devoted to the modeling and numerical optimization of proton-exchange membrane (PEM) water electrolysers for operation at elevated pressures (up to 130 bars). The model takes into account different geometrical parameters of the PEM cell, the kinetics of the hydrogen and oxygen evolution reactions, the electro-osmotic drag of water molecules, the permselectivity of the solid polymer electrolyte and associated gas cross-over phenomena. The role of various operating parameters (such as pressure, temperature, current density, flow rate of water) on cell efficiency, faradaic yield and heat produced during water electrolysis is evaluated and discussed. The model is also used for the purpose of optimizing the performances of PEM cells. In particular, optimal values of some critical operating parameters (current density, rate of water supplied to the anodes) are recommended.

Adsorption, synergistic inhibitive effect and quantum chemical studies of ampicillin (AMP) and halides for the corrosion of mild steel in H2SO4

Abstract: The corrosion inhibition of ampicillin (AMP) and its synergistic combination with halides (KI, KCl and KBr) for the corrosion of mild steel in H2SO4 have been investigated using gravimetric, gasometric, thermometric and infrared (IR) methods. The inhibition efficiencies of AMP for the corrosion of mild steel increased with increase in concentration but decreased with rise in temperature. The adsorption of AMP on the mild steel surface was found to obey the Langmuir adsorption isotherm model. The combination of AMP with the halides (KI, KBr and KCl) enhanced the inhibition efficiency and adsorption behavior of the inhibitor indicating synergism. The inhibition efficiency of AMP increased with increasing concentration and the adsorption of the inhibitor was spontaneous. Physical adsorption mechanism has been proposed from the thermodynamic data obtained. There was a significant correlation between the inhibition efficiency of AMP and some quantum chemical parameters (R 2 = 0.96) using the quantitative structure–activity relationship (QSAR) method. Some quantum chemical parameters and the Mulliken charge densities on the optimized structure of AMP were calculated using the B3LYP/6-31G (d,p) basis set method to provide further insight into the mechanism of the corrosion inhibition process.

Electrodeposited Zn–TiO2 nanocomposite coatings and their corrosion behavior

Abstract: The present paper aims to investigate the electrodeposition on steel substrate and the corrosion behavior of Zn–TiO2 nanocomposite coatings. Zn–TiO2 composite coatings were electrodeposited on OL 37 steel from an electrolyte containing ZnCl2, KCl, HBO3 (pH 5.7) brightening agents and dispersed nanosized TiO2. Corrosion measurements were performed in 0.2 g L−1 (NH4)2SO4 solution (pH 3) by using electrochemical methods (open-circuit potential measurements, polarization curves, electrochemical impedance spectroscopy). The results of electrochemical measurements were corroborated with those obtained by using non-electrochemical methods (X-ray diffraction, atomic force microscopy and scanning electron microscopy). The results indicate that the composite coatings exhibit higher corrosion resistance as compared to pure Zn coatings and a non-linear dependence of their polarization resistance on TiO2 concentration in the plating bath was found. The importance of TiO2 nature and concentration regarding the properties of the composite coatings was demonstrated.

The electrochemical performance of lithium–sulfur batteries with LiClO4 DOL/DME electrolyte

Abstract: The electrochemical performance of lithium–sulfur batteries with LiClO4 DOL/DME as electrolyte was investigated. Impedance and SEM analysis indicated that too high content of DME(Dimethoxy ethane) in electrolyte could raise the interfacial resistance of battery due to the impermeable layer formed on the surface of the sulfur cathode, which led to bad cycle performance, while the increase of DOL(1,3-dioxolane) could change those phenomena. The optimal composition of electrolyte was DME:DOL = 2:1 (v/v). With this electrolyte, the lithium–sulfur battery obtained a high initial discharge capacity of 1,200 mA h g−1 and still remained 800 mA h g−1 after 20 cycles.

Inhibiting effects of 5-substituted isatin-based Mannich bases on the corrosion of mild steel in hydrochloric acid solution

Abstract: The inhibition effect of all the three Mannich bases against the corrosion of mild steel in 1 M HCl solution was studied by weight loss, electrochemical impedance spectroscopy (EIS), potentiodynamic polarization, and atomic force microscopy techniques. Data obtained from EIS studies were analyzed to model the corrosion inhibition process through appropriate equivalent circuit models. The adsorption of Mannich bases obeyed Langmuir adsorption isotherm. Both thermodynamic and activation parameters were calculated and discussed. Polarization curves indicate that they are mixed type of inhibitors. All the Mannich bases were adsorbed physically at lower concentration, whereas chemisorption was favored at higher concentration. The results obtained from weight loss, EIS, and Potentiodynamic polarization are in good agreement.

Developments in the soluble lead-acid flow battery

Abstract: The history of soluble lead flow batteries is concisely reviewed and recent developments are highlighted. The development of a practical, undivided cell is considered. An in-house, monopolar unit cell (geometrical electrode area 100 cm2) and an FM01-LC bipolar (2 × 64 cm2) flow cell are used. Porous, three-dimensional, reticulated vitreous carbon (RVC) and planar, carbon-HDPE composite electrodes have been used in laboratory flow cells. The performance of such cells under constant current density (10–160 mA cm−2) cycling is examined using a controlled flow rate (mean linear flow velocity <14 cm s-1) at a temperature of approximately 298 K. Voltage versus time and voltage versus current density relationships are considered. High charge (<90%), voltage (<80%) and energy (<70%) efficiencies are possible. Possible failure modes encountered during early scale-up from a small, laboratory flow cell to larger, pilot-scale cells are discussed.

Inhibition by Jasminum nudiflorum Lindl. leaves extract of the corrosion of cold rolled steel in hydrochloric acid solution

Abstract: The inhibition effect of Jasminum nudiflorum Lindl. leaves extract (JNLLE) on the corrosion of cold rolled steel (CRS) in 1.0 M hydrochloric acid (HCl) was investigated by weight loss, potentiodynamic polarization, and electrochemical impedance spectroscopy (EIS) methods. The results show that JNLLE acts as a very good inhibitor, and the inhibition efficiency increases with the concentration of JNLLE. The adsorption of JNLLE obeys Langmuir adsorption isotherm. Values of inhibition efficiency obtained from weight loss, potentiodynamic polarization, and electrochemical impedance spectroscopy (EIS) are in good agreement. Polarization curves show that JNLLE behaves as a mixed-type inhibitor in hydrochloric acid. EIS shows that charge-transfer resistance increase and the capacitance of double layer decreases with the inhibitor concentration, confirming the adsorption process mechanism. The adsorbed film on CRS surface containing JNLLE inhibitor was also measured by Fourier transform infrared spectroscopy (FTIR) and scanning electron microscope (SEM). A probable inhibitive mechanism is proposed from the viewpoint of adsorption theory.

A microbial fuel cell using manganese oxide oxygen reduction catalysts

Abstract: Microbial fuel cells (MFCs) are a potential method for enhanced water and waste treatment, which offer the additional benefit of energy generation. Manganese oxide was prepared by a simple chemical oxidation using potassium permanganate. Carbon-supported manganese oxide nanoparticles were successfully characterised as cathode materials for MFCs. The manganese oxide particles when used in a two-chamber MFC, using inoculum from an anaerobically digested sewage sludge, were found to exhibit similar oxygen reduction performance to that in separate electrochemical tests. MFC tests were conducted in a simple two chamber cell using aqueous air-saturated catholytes separated from the anode chamber by a Nafion membrane. MFC peak power densities were ca. 161 mW m−2 for MnO x /C compared to 193 mW m−2 for a benchmark Pt/C, in neutral solution at room temperature. The catalyst materials demonstrated good stability in the 7.0–10.0 pH range. Theoretical (IR free) peak power densities were 937 mW m−2 for MnO x /C compared with 1037 mW m−2 for Pt/C in the same experimental conditions: showing the MFCs performances can easily be improved by using more favourable conditions (more conductive electrolyte, improved cathode catalyst etc.). Our studies indicated that the use of our low cost MnO x /C catalysts is of potential interest for the future application of MFC systems.

Preparation and electrochemical performance of Li-rich layered cathode material, Li[Ni0.2Li0.2Mn0.6]O2, for lithium-ion batteries

Abstract: The Li-rich layered cathode material, Li[Ni02Li02Mn06]O2, was synthesized via a “mixed oxalate” method, and its structural and electrochemical properties were compared with the same material synthesized by the sol–gel method X-ray diffraction (XRD) shows that the synthesized powders have a layered O3–LiCoO2-type structure with the R-3m symmetry X-ray photoelectron spectroscopy (XPS) indicates that in the above material, Ni and Mn exist in the oxidation states of +2 and +4, respectively The layered material exhibits an excellent electrochemical performance Its discharge capacity increases gradually from the initial value of 228 mA hg−1 to a stable capacity of over 260 mA hg−1 after the 10th cycle It delivers a larger capacity of 258 mA hg−1 at the 30th cycle The dQ/dV curves suggest that the increasing capacity results from the redox-reaction of Mn4+/Mn3+

DSA electrochemical treatment of olive mill wastewater on Ti/RuO2 anode

Abstract: The electrochemical oxidation of olive mill wastewater (OMW) over a Ti/RuO2 anode was studied by means of cyclic voltammetry and bulk electrolysis and compared with previous results over a Ti/IrO2 anode. Experiments were conducted at 300–1,220 mg L−1 initial chemical oxygen demand (COD) concentrations, 0.05–1.35 V versus SHE and 1.39–1.48 V versus SHE potential windows, 15–50 mA cm−2 current densities, 0–20 mM NaCl, Na2SO4, or FeCl3 concentrations, 80 °C temperature, and acidic conditions. Partial and total oxidation reactions occur with the overall rate being near first-order kinetics with respect to COD. Oxidation at 28 Ah L−1 and 50 mA cm−2 leads to quite high color and phenols removal (86 and 84%, respectively), elimination of ecotoxicity, and a satisfactory COD and total organic carbon reduction (52 and 38%, respectively). Similar performance can be achieved at the same charge (28 Ah L−1) using lower current densities (15 mA cm−2) but in the presence of various salts. For example, COD removal is less than 7% at 28 Ah L−1 in a salt-free sample, while addition of 20 mM NaCl results in 54% COD reduction. Decolorization of OMW using Ti/RuO2 anode seems to be independent of the presence of salts in contrast with Ti/IrO2 where addition of NaCl has a beneficial effect on decolorization.

An interesting and efficient green corrosion inhibitor for aluminium from extracts of Chlomolaena odorata L. in acidic solution

Abstract: The leaf extracts of Chromolaena odorata L. (LECO) has been studied as a possible source of green inhibitor for corrosion of aluminium in 2 M HCl using gasometric and thermometric techniques at 30 and 60 °C. Results obtained showed that the LECO functioned as an excellent corrosion inhibitor for aluminium in the acidic environment. Inhibition efficiency increased with extract concentration but decreased with temperature. The adsorption of LECO on Al surface is in accord with Langmuir adsorption isotherm. Both kinetic and thermodynamic parameters governing the adsorption process were calculated and discussed. From the experimental results obtained, it can be concluded that LECO which are biodegradable, environmentally benign, and are obtained from a renewable resource with minimal health and safety concerns have the potential to be a cost effective alternative to synthetic corrosion inhibitors. This present study provides new information on the inhibiting characteristics of LECO extract under specified conditions. The environmentally friendly inhibitor could find possible applications in metal surface anodizing and surface coating in industries.

Recent developments and trends in the electrochemical promotion of catalysis (EPOC)

Abstract: Electrochemical Promotion of Catalysis (EPOC or NEMCA effect) is one of the most exciting discoveries in Electrochemistry with great impact on many catalytic and electrocatalytic processes. According to the words of John O’M. Bockris, EPOC is a triumph, and the latest in a series of advances in electrochemistry which have come about in the last 30 years. It has been shown with more than 80 different catalytic systems that the catalytic activity and selectivity of conductive catalysts deposited on solid electrolytes can be altered in a very pronounced, reversible and, to some extent, predictable manner by applying electrical currents or potentials (typically up to ±2 V) between the catalyst and a second electronic conductor (counter electrode) also deposited on the solid electrolyte. The induced steady-state change in catalytic rate can be up to 135 × 103% higher than the normal (open-circuit) catalytic rate and up to 3 × 105 higher than the steady-state rate of ion supply. EPOC studies in the last 7 years mainly focus on the following four areas: Catalytic reactions with environmental impact (such as reduction of NOx and oxidation of light hydrocarbons), mechanistic studies on the origin of EPOC (using mainly oxygen ion conductors), scale-up pf EPOC reactors for potential commercialization via development of novel compact monolithic reactors and application of EPOC in high or low temperature fuel cells via introduction of the concept of triode fuel cell. The most recent EPOC studies in these areas are discussed in the present review and some of the future trends and aims of EPOC research are presented.

Amperometric hydrogen peroxide biosensor based on a modified gold electrode with silver nanowires

Abstract: A novel amperometric biosensor for the detection of hydrogen peroxide (H2O2) was prepared by immobilizing horseradish peroxidase (HRP) on highly dense silver nanowire (Ag-NW) film. The modified electrode was characterized using UV–Vis spectroscopy, scanning electron microscopy, X-ray diffraction, and transmission electron microscopy. The electrochemical performances of the electrode were studied by cyclic voltammetry and chronoamperometry. The HRPs immobilized on the surface of Ag-NWs exhibited an excellent electrocatalytic response toward reduction of H2O2. The resulting Ag-NW modified sensor showed a sensitivity of ~2.55 μA μM−1 (correlation coefficient r = 0.9969) with a linear range of 4.8 nM–0.31 μM. Its detection limit was 1.2 nM with a signal-to-noise ratio of 3. The Michaelis–Menten constant K M app and the maximum current density I max of the modified electrode were 0.0071 mM and 8.475 μA, respectively. The preparation process of the proposed biosensor was convenient, and the resulting biosensor showed high sensitivity, low detection limit and good stability.

Electrochemical process for the treatment of landfill leachate

Abstract: In this paper, the anodic oxidation of a real leachate from an old municipal solid waste landfill has been studied using an electrolytic flow cell equipped with a lead dioxide (PbO2) anode and stainless steel as the cathode. The influence of several operation parameters such as (i) the applied current (from 0.5 to 3 A), (ii) liquid flow rate (from 50 to 420 L h−1), (iii) temperature (from 25 to 50 °C), and (iv) pH (from 3.5 to 8.2) on the COD removal rate, current efficiency, and energy consumption has been evaluated. The galvanostatic electrolyses always yielded COD values below the discharge limit (COD <160 mg L−1); the COD removal rate increased with rising applied current, solution pH, and temperature, whereas it remained almost unaffected by the recirculation flow rate. These results indicate that the organic compounds were mainly removed by their indirect oxidation by the active chlorine generated from chlorides oxidation. The specific energy consumption necessary to reduce the organic load to below the disposal limit was 90 kWh m−3.

Modelling microbial fuel cells with suspended cells and added electron transfer mediator

Abstract: Derivation of a mathematical model for microbial fuel cells (MFC) with suspended biomass and added electron-transfer mediator is described. The model is based on mass balances for several dissolved chemical species such as substrate, oxidized mediator and reduced mediator. Biological, chemical and electrochemical reactions can occur in the bulk liquid and at the electrode surface, respectively. Model outputs include time-dependent production of current and electrical charge, current–voltage and current–power curves, and the evolution of concentrations of chemical species. The model behaviour is illustrated using a test case based on detailed experimental observations reported in the literature for a microbial fuel cell operated in batch mode and repeatedly fed with a single substrate. A detailed model parameter estimation procedure is presented. The model simulates the current–time evolution and voltage–current curves in the MFC with glucose as anode substrate and the ferrocyanide/ferricyanide redox couple as the oxidation reaction at the cathode. Simulations show the effect of different parameters (electrical resistance, mass transfer resistance, exchange current, coulombic yields and biomass, substrate and mediator concentrations) on the MFC characteristics. The model explains how the endogenous metabolism or intracellular substrate storage could lead to a non-zero background current even when the added substrate has been depleted. Different trends (increasing or decreasing) in the initial current are explained by the initial oxidation state of the mediator (oxidized or reduced, respectively). The model has potential applications for other bioelectrochemical systems.

Electrodialytic remediation of copper mine tailings with sinusoidal electric field

Abstract: In this work an electrodialytic remediation cell for copper mine tailings using sinusoidal electric field was analyzed, in order to increase the removal efficiency. The sinusoidal electric field was obtained by applying simultaneously continuous-alternating voltages; in this work an alternating voltage of low frequency was applied. The system was tested considering the effect of: (1) the effective voltage applied to the cell, (2) the period for the alternating voltage, (3) remediation time, and (4) copper complexing capacity of citric acid. According to the conditions studied in this investigation, the laboratory results showed that decreasing the effective voltage improves the remediation action, due to polarity reversal of the system, which reduces polarization during the process, but in terms of the period for the alternating voltage there is no effect. As expected the remediation time and copper complexing capacity of citric acid improves the amount of remediated material and the remediation action in general.

Potentiometric determination of the chloride ion activity in cement based materials

Abstract: The chloride content at the reinforcement is one of the decisive factors for the initiation and propagation of localised corrosion in concrete structures. A monitoring technique for the chloride concentration which is accurate, non-destructive and continuous would thus be highly desirable. For this reason, the performance of ion selective electrodes (ISEs) was investigated both in alkaline solutions and embedded in mortar. The Ag/AgCl electrodes used in this work showed Nernstian behaviour with a slope of –59 ± 1 mV per decade and a detection limit for chloride ions below 10−2 mol dm−3 even at pH close to 14; the selectivity coefficient for hydroxide interference was estimated at $$ k_{{{\text{Cl}}^{ - } ,{\text{OH}}^{ - } }}^{\text{pot}} \approx 4 \cdot 10^{ - 3} $$ . The Ag/AgCl membranes show good long-term stability over more than 6 months even in highly alkaline solutions as long as chloride ions are present; in the complete absence of chloride the measured potentials were affected by the pH of the solution. The sensors are, however, able to recover fast as soon as they come into contact with chloride. When using ISEs embedded in concrete, diffusion potentials between the reference electrode and the ISE, as arising e.g. from gradients in pH, significantly affect the potential measurement and present a most important error source for the application of direct potentiometry to concrete. To minimise such errors, the reference electrode has to be positioned as close to the ISE as possible.

Antibacterial drugs as inhibitors for the corrosion of stainless steel type 304 in HCl solution

Abstract: The effect of three antibacterial drugs (3-thiazinonyl-bicyclo [4.2.0] octene-carboxylate derivatives) on the corrosion behavior of stainless steel type 304 in 1.0 M HCl solution has been investigated using weight loss, potentiodynamic polarization, and electrochemical impedance spectroscopy (EIS) techniques. The inhibition efficiency increased with increase in inhibitor concentration but decreased with increase in temperature. The thermodynamic functions of corrosion and adsorption processes were evaluated. The potentiodynamic polarization measurements indicated that the inhibitors are of mixed type. The adsorption of these inhibitors was found to obey Langmuir’s adsorption isotherm. Synergism between iodide ion and inhibitors was proposed. The inhibitive action was satisfactory explained by using both thermodynamic and kinetic models. The results obtained from the three different techniques were in good agreement.

Electrochemical degradation of Reactive Red 120 using DSA and BDD anodes

Abstract: Electrochemical oxidation of an azo dye (Reactive Red 120) was studied in acidic media (1 M HClO4) using DSA type (Ti/IrO2-RuO2) and boron doped diamond (BDD) anodes. Ti/IrO2-RuO2 exhibited low oxidation power with high selectivity to organic interme- diates and low TOC removal (10% at 25 C and 40% at 80 C). On the other hand BDD was found to be suitable for total mineralization of the organic loading to CO2 .I n both cases, the decoloration of the solution was almost 100% achieved very quickly with BDD (2 Ah L -1 ) but only after long treatment with Ti/IrO2-RuO2 (25 Ah L -1 ). The instantaneous current efficiency (ICE) was up to 0.13 in the case of Ti/IrO2-RuO2 and up to 0.45 in the case of BDD.

Electroxidation of oxalic acid at different electrode materials

Abstract: Oxalic acid is one of the proposed metabolites of the anodic oxidation of more complex organic molecules In spite of its simple structure, its mineralization strongly depends on the nature of the electrode material at which the process is carried out Sargisyan and Vasil’ev (Elektrokhimiya 18:845, 1982) pointed out such dependence, investigating the kinetic behavior of OA at different metal (Rh, Pd, Os, Ir, Pt and Au), at dimensionally stable anodes (RuO2–TiO2) and at glassy carbon (GC) electrodes Their conclusions highlighted the important role played by the organic anion adsorption step, claiming that OA is oxidized with increasing difficulty at electrode materials having higher oxygen affinity More recently, these assumptions have been supported by data on OA oxidation at high anodic potentials (Martinez-Huitle et al, Electrochim Acta 49:4027, 2004) To further enrich the picture, in the present paper, kinetic investigations were carried out at different mixed-oxides, Pt, GC and highly conductive, boron-doped diamond (BDD) electrodes, with either oxygen or fluorine at their surface

On the activation and physical degradation of boron-doped diamond surfaces brought on by cathodic pretreatments

Abstract: The electrochemical activation and physical degradation of boron-doped diamond (BDD) electrodes with different boron doping levels after repeated cathodic pretreatments are reported. Galvanostatic cathodic pretreatment passing up to −14000 C cm−2 in steps of −600 C cm−2 using −1 A cm−2 caused significant physical degradation of the BDD surface, with film detachment in some areas. Because of this degradation, a great increase in the electrochemically active area was observed in Tafel plots for the hydrogen evolution reaction (HER) in acid media. The minimum cathodic pretreatment needed for the electrochemical activation of the BDD electrodes without producing any observable physical degradation on the BDD surfaces was determined using electrochemical impedance spectroscopy (EIS) measurements and cyclic voltammetry: −9 C cm−2, passed at −1 A cm−2. This optimized cathodic pretreatment can be safely used when electrochemical experiments are carried out on BDD electrodes with doping levels in the range between 800 and 8000 ppm.

Investigation of triazole derived Schiff bases as corrosion inhibitors for mild steel in hydrochloric acid medium

Abstract: 3,5-Diamino-1,2,4-triazole Schiff base derivatives and their inhibition efficiency, based on the effect of changing functional groups, were reported to establish a relationship between inhibitor efficiency and molecular structure using weight loss method, electrochemical and Fourier transform infrared spectral techniques. It was found that the molecules containing more electron donating groups have higher inhibition efficiency than the corresponding compounds with low electron donating groups. The results indicate that the order of inhibition efficiency of the triazole and its Schiff bases in solution and the extent of their tendency to adsorb on mild steel surfaces are as follows: vanilidine 3,5-diamino-1,2,4-triazole > furfuraldine 3,5-diamino-1,2,4-triazole > anisalidine 3,5-diamino-1,2,4-triazole > 3,5-diamino-1,2,4-triazole.

Structural analyses of RuO 2 –TiO 2 /Ti and IrO 2 –RuO 2 –TiO 2 /Ti anodes used in industrial chlor-alkali membrane processes

Abstract: The morphology and composition of RuO2–TiO2/Ti and IrO2–RuO2–TiO2/Ti anodes, which have been used for the production of chlorine for more than 10 years, were analyzed by various methods; such as high-resolution scanning electron microscopy, high-resolution Auger electron spectroscopy, electron probe X-ray emission microanalysis and X-ray diffraction analysis. Drastic changes in the surface morphology, including partial exfoliation of a small amount of the oxide layer and a reduction in the content of ruthenium species through dissolution, were observed for the RuO2–TiO2/Ti anode. For the IrO2–RuO2–TiO2/Ti anode, on the other hand, there were moderate changes in the surface morphology and moderate dissolution of iridium and ruthenium species.

Pulsed electrokinetic removal of Cd and Zn from fine-grained soil

Abstract: Pulsed electrokinetics studies were carried out to optimize the removal of Zn and Cd from fine-grained soils and to observe the effects of varying the pulse frequency, pulse time ratio (on/off), and DC voltage gradient. Existing forms of heavy metals in the soil matrix were determined using a sequential extraction method. The strongly bound fraction (bound to organic matter and residuals) that is difficult to remove from the soil matrix comprised 74 and 62% of the total Zn and Cd, respectively. In the electrokinetic remediation experiments, MgSO4 was employed to increase the ionic strength of the soil for 2 weeks. Transportation of heavy metals was influenced by the frequency, pulse ratio, and the voltage gradient of the pulsed electric field. Extraction efficiency of Zn and Cd near the anode was correlated positively with the voltage gradient at a given pulse and ratio. A high pulse frequency (1,800 cycles/h) enhanced the removal efficiency of the heavy metals compared to a low pulse frequency (1,200 cycles/h) at a supplied voltage gradient of 1 V/cm. Although pulsed electrokinetics was more effective in extracting and desorbing ions near the anode than conventional electrokinetics, its ability to transport heavy metals from the anode to the cathode was relatively small. Total removals with pulsed electrokinetics were 21–31% for Zn and 18–24% for Cd. In summary, pulsed electrokinetics can enhance removal efficiency of heavy metals and is beneficial with regard to electrical energy consumption.

Heterogeneous photo-electro-Fenton process using different iron supporting materials

Abstract: In this work, the application of heterogeneous photo-electro-Fenton processes using iron supported on Nafion membranes and ion exchange amberlite and purolite resins is studied Spectroscopic and TOC results using as a model pollutant an aqueous Orange II dye solution indicate that the process can be carried out with any of the iron supporting materials under study While the resins can incorporate between 59 and 65 mg Fe/g of substrate, a Nafion membrane can fix 45 mg Fe/g of supporting material Iron desorption analysis after a photo-electro-Fenton degradation test on the other hand, indicates that the ion exchange resins and the Nafion membrane hold more than 90% of iron An alkaline rinse after the activation exchange process for the amberlite resin and the Nafion membrane, results in a larger stability of the fixed iron species

Effect of some tripodal bipyrazolic compounds on C38 steel corrosion in hydrochloric acid solution

Abstract: The corrosion inhibition of C38 steel in molar HCl by N,N-bis[2-(3,5-dimethyl-1H-pyrazol-1-yl)ethyl]buthylamine (P1) and 5-{N,N-bis[2-(3,5-dimethyl-1H-pyrazol-1-yl)ethyl] amino} pentanol (P2) has been investigated at 308 K using electrochemical and weight loss measurements. Measurements show that these compounds act as good inhibitors without changing the mechanism of the corrosion process. Moreover, the inhibiting efficiency increases with the increase in concentration of the studied inhibitors. Compound P2 showed better protection properties even at relatively higher temperatures when compared to P1. The associated activation corrosion and free adsorption energies have been determined. P1 and P2 are adsorbed on the C38 steel surface according to a Langmuir isotherm adsorption model.

The use of macrocyclic compounds as electrocatalysts in fuel cells

Abstract: Macrocyclic compounds such as metallophthalocyanines demonstrated good catalytic activities toward electrochemical reactions. The characteristics of the central cations in metallophthalocyanines significantly influenced their electrocatalytic activities. Addition of conjugated polymers in electrodes improved the electrocatalytic activity by enhancing the electric conductivity. The electrocatalytic activities of macrocyclic compounds could be further improved by heat treatment. The formation of metallic clusters or metal containing organic fragments after pyrolyzing played an important role in improving electrocatalytic activities of macrocyclic compounds. It was considered that macrocyclic compounds might be functioned as a precursor to obtain well-distributed metallic clusters or metal containing organic fragments.

Electrochemical impedance spectroscopy and cyclic voltammetry of ferrocene in acetonitrile/acetone system

Abstract: The oxidation of ferrocene (FeCp2) to ferrocenium cation (FeCp 2 + ) (where Cp: cyclopentadienyl anion, C5H5 −) was investigated by means of electrochemical impedance spectroscopy (EIS) and cyclic voltammetry (CV) on either platinum (Pt) or glassy carbon (G-C) electrodes in acetonitrile (ACN), acetone (ACE), and acetonitrile (ACN)/acetone (ACE) binary mixtures with n-tetrabutylammonium hexafluorophosphate (TBAPF6) as background electrolyte at T = 294.15 K. The half-wave potentials (E 1/2), the diffusion coefficients (D), and the heterogeneous electron-transfer rate constants (k s) were derived. The activation free energies for electron transfer (ΔG exp ) were experimentally determined and compared with the theoretical values (ΔG cal ). The electron-transfer process was reversible and diffusion-controlled in all investigated solvent mixtures. The changes on the metal–ligand bond lengths upon electron transfer were almost insignificant. The E 1/2 values were shifted to less positive potentials with the increase of the ACN content. The k s values obtained on Pt electrode were slightly larger compared to k s measured on G-C electrode, while in both cases the k s values were diminished with the enrichment of the mixtures in ACN. The EIS spectra confirmed that the rate-determining step in the whole process is the diffusion of the FeCp2 species and thus the process can be properly characterized as diffusion-controlled.