Fe Electrodes Research Articles

In-situ grazing incidence X-ray diffraction measurements of relaxation in Fe/MgO/Fe epitaxial magnetic tunnel junctions during annealing

The relaxation of Fe/MgO/Fe tunnel junctions grown epitaxially on (001) MgO substrates has been measured by in-situ grazing incidence in-plane X-ray diffraction during the thermal annealing cycle. We find that the Fe layers are fully relaxed and that there are no irreversible changes during annealing. The MgO tunnel barrier is initially strained towards the Fe but on annealing, relaxes and expands towards the bulk MgO value. The strain dispersion is reduced in the MgO by about 40% above 480K post-annealing. There is no significant change in the “twist” mosaic. Our results indicate that the final annealing stage of device fabrication, crucial to attainment of high TMR, induces substantial strain relaxation at the MgO barrier/lower Fe electrode interface.

Investigation of technical and economic analysis of electrocoagulation process for the treatment of great and small cattle slaughterhouse wastewater

In this study, the treatment of slaughterhouse wastewater by electrocoagulation (EC) was investigated in batch reactor using aluminum and iron electrodes. Effects of operating parameters for the EC process such as initial pH solution (3–8), current density (20–140 A/m2) and operation time of EC (2.5–60 min) were evaluated for optimum operating conditions. The removal efficiencies for COD, oil-grease and turbidity in slaughterhouse wastewaters were obtained to be 78.3, 94.7, and 90.2% for aluminum and 76.7, 92.8, and 95.9% for iron electrodes at the optimum conditions (pH 4, 100 A/m2, and 20 min EC time for Al; pH 6, 100 A/m2, and 20 min EC time for Fe). Operation costs for removal of slaughterhouse wastewater at the optimum conditions were calculated for Al electrodes as 2.757 $/m3 and for Fe electrodes as 0.872 $/m3. Besides, the treatment performance of EC and chemical coagulation (CC) processes were compared. For CC process, aluminum sulfate, ferric chloride, and ferric sulfate as coagulants were compared. COD, oil-grease, and turbidity removal efficiencies were 36.4, 93.6, and 89.8% for Al2(SO4)3.18H2O (pH 7–200 mg Al3+/l), 27.6, 88.6, and 85.9% for FeSO4.7H2O(pH 7–200 mg Fe3+/l), and 37.4, 89.9, and 75.6% FeCl3.6H2O (pH 7–100 mg Fe3+/l), respectively. As a result, the EC process is more effective in COD, oil-grease, and turbidity removal efficiencies than CC process.

Electron transfer capacity dependence of quinone-mediated Fe(III) reduction and current generation by Klebsiella pneumoniae L17

Quinone groups in exogenous electron shuttles can accelerate extracellular electron transfer (EET) from bacteria to insoluble terminal electron acceptors, such as Fe(III) oxides and electrodes, which are important in biogeochemical redox processes and microbial electricity generation. However, the relationship between quinone-mediated EET performance and electron-shuttling properties of the quinones remains incompletely characterized. This study investigates the effects of a series of synthetic quinones (SQs) on goethite reduction and current generation by a fermenting bacterium Klebsiella pneumoniae L17. In addition, the voltammetric behavior and electron transfer capacities (ETCs) of SQ, including electron accepting (EAC) and donating (EDC) capacities, is also examined using electrochemical methods. The results showed that SQ can significantly increase both the Fe(III) reduction rates and current outputs of L17. Each tested SQ reversibly accepted and donated electrons as indicated by the cyclic voltammograms. The EAC and EDC results showed that Carmine and Alizarin had low relative capacities of electron transfer, whereas 9,10-anthraquinone-2,6-disulfonic acid (AQDS), 2-hydroxy-1,4-naphthoquinone (2-HNQ), and 5-hydroxy-1,4-naphthoquinone (5-HNQ) showed stronger relative ETC, and 9,10-anthraquinone-2-carboxylic acid (AQC) and 9,10-anthraquinone-2-sulfonic acid (AQS) had high relative ETC. Enhancement of microbial goethite reduction kinetics and current outputs by SQ had a good linear relationship with their ETC, indicating that the effectiveness of quinone-mediated EET may be strongly dependent on the ETC of the quinones. Therefore, the presence of quinone compounds and fermenting microorganisms may increase the diversity of microbial populations that contribute to element transformation in natural environments. Moreover, ETC determination of different SQ would help to evaluate their performance for microbial EET under anoxic conditions.

Decolorization Treatment of Copper Phthalocyanine Textile Dye Wastewater by Electrochemical Methods

Electrochemical decolorization and degradation treatment of aqueous copper phthalocyanine reactive dye solutions was comparatively studied by electrocoagulation, electrooxidation and electro-Fenton processes. In the electrocoagulation process with aluminum electrodes the colored aqueous solutions of initial pH 6.4 containing 50 mg L-1 copper phthalocyanine and 6 g L-1 NaCl were treated at applied current densities of 2.5 and 5 mA cm-2. Fast and 100% decolorization was achieved in 4 and 2 minutes of electroprocessing respectively. The indirect electrooxidation process was conducted in acidic electrolyte solutions containing 50 mg L-1 copper phthalocyanine and 6 g L-1 NaCl with Ti/Pt and graphite plate electrodes at the applied current density of 10 mA cm-2. Even after 90 minutes of electrolysis time the dye remained by 23 and 18.8 % respectively undegradable. By the direct and indirect electrooxidation with the same amount of Na2SO4 electrolyte and added H2O2 respectively and using the same electrodes, the copper phthalocyanine dye was not or was only barely degraded respectively. In the electro-Fenton process with Fe electrodes and added amounts of H2O2 at pH 3 and an applied current density of 5 mA/cm2 complete degradation of copper phthalocyanine occurred in 15 minutes.

Detailed analysis of spin-dependent quantum interference effects in magnetic tunnel junctions with Fe quantum wells

We investigated spin-dependent quantum interference effects in Cr(001)/wedge Fe(001)/MgO(001)/Fe(001) magnetic tunnel junctions by dI/dV measurements. dI/dV intensities were mapped two-dimensionally as a function of applied voltage and Fe thickness, indicating a clear signature of quantum well (QW) states in the ultrathin Fe (001) electrode. However, resonant positions of QW states were systematically shifted by one monolayer when compared with the first-principles calculation results. X-ray absorption spectroscopy and magnetic circular dichroism measurements were also performed. While Fe oxide presence at Fe/MgO interface was ruled out, Fe/Cr intermixing could not be excluded. Hence, controlling the Fe/Cr interface may affect QW state.

Highly sensitive amperometric sensor for micromolar detection of trichloroacetic acid based on multiwalled carbon nanotubes and Fe(II)–phtalocyanine modified glassy carbon electrode

A highly sensitive electrochemical sensor for the detection of trichloroacetic acid (TCA) is developed by subsequent immobilization of phthalocyanine (Pc) and Fe(II) onto multiwalled carbon nanotubes (MWCNTs) modified glassy carbon (GC) electrode. The GC/MWCNTs/Pc/Fe(II) electrode showed a pair of well-defined and nearly reversible redox couple correspondent to (Fe(III)Pc/Fe(II)Pc) with surface-confined characteristics. The surface coverage (Γ) and heterogeneous electron transfer rate constant (ks) of immobilized Fe(II)–Pc were calculated as 1.26×10−10molcm−2 and 28.13s−1, respectively. Excellent electrocatalytic activity of the proposed GC/MWCNTs/Pc/Fe(II) system toward TCA reduction has been indicated and the three consequent irreversible peaks for electroreduction of CCl3COOH to CH3COOH have been clearly seen. The observed chronoamperometric currents are linearly increased with the concentration of TCA at concentration range up to 20mM. Detection limit and sensitivity of the modified electrode were 2.0μM and 0.10μAμM−1cm−2, respectively. The applicability of the sensor for TCA detection in real samples was tested. The obtained results suggest that the proposed system can serve as a promising electrochemical platform for TCA detection.

Electrocoagulation of synthetic dairy wastewater

This study compares the effectiveness of pollutant removal from synthetic dairy wastewater electrocoagulated by means of aluminum and iron anodic dissolution. A method based on the cubic function (third degree polynomial) was proposed for electrocoagulant dosing. Mathematical methods for calculating the optimal electrocoagulant doses proved to be quite precise and useful for practical applications. The results of gravimetric measurements of electrocoagulant (electrode) consumption demonstrated that theoretical doses of Al determined based on Faraday's law were substantially lower than those produced by electrode weighing. The above phenomenon was also discussed in the light of the results of polarization resistance measurements for Al and Fe electrodes used in the study.

In Situ Electrokinetic Removal of Salts from Greenhouse Soil Using Iron Electrode

An electrokinetic (EK) field study was performed on a pilot scale (2.2 × 3.3 × 0.3 m3, W × L × D) in a greenhouse by using Fe electrodes and bentonite backfill. When a constant voltage gradient was applied, the current intensity was affected by electrode position, and the soil temperature increased with the current intensity. After the EK treatment, the soil pH was little changed and the cations were hardly removed because of the ion exchange in the bentonite. However, the anions were mostly removed by electromigration, resulting in the reduction of the soil electrical conductivity. The field study demonstrated that in situ EK process is feasible for the remediation of greenhouse soils. In addition, the improvement of EK system and the role of bentonite backfill were discussed.

SERS Investigation of the Interfacial Structure at Fe Electrode in Ionic Liquids

SERS Investigation of the Interfacial Structure at Fe Electrode in Ionic Liquids

Electrocatalytic Activation of Aromatic Carbon-Bromine Bonds toward Carboxylation at Silver and Copper Cathodes

The electrocatalytic activation of the carbon-bromine bond in susbstituted bromobenzenes has been studied in dimethylformamide (DMF) at Ag, Au, Cu, Fe, Ni, Pd, Pt and Zn electrodes. The electrocatalytic properties of these metals have been evaluated by comparing reduction peak potentials, Ep, of C6H5Br at such electrodes with Ep measured for the same compound at glassy carbon (GC). Only Ag, Cu and Au show remarkable electrocatalytic properties with positive shifts of Ep between 0.42 and 0.69 V with respect to GC. Ag, Cu and Au show also good catalytic activities for various substituted bromobenzenes (ArBr). The possibility of exploiting the electrocatalytic activation of ArBr for the synthesis of benzoic acids has also been investigated. In CO2-saturated DMF, Ag and Cu show high conversions of ArBr with moderate to good yields of ArCO2H. In all cases hydrodebromination to ArH is in competition with carboxylation, the relative importance of the two reactions strongly depending on the substituent as well as on the nature of the electrode material. Instead, Au does not show good selectivity for the reduction of ArBr, electroreduction of CO2 being always concomitant with, and sometimes even more favorable than, that of ArBr.

First-principles Study of Bias Effect on Magnetoresistance of Fe/MgO/Fe Tunnel Junctions

ABSTRACTWe studied the transport properties of the Fe/MgO/Fe and Fe/Ag/MgO/Ag/Fe magnetic tunnel junctions (MTJs) with 13-layer MgO barrier under bias voltage based on first-principles calculations. Our results showed that two features determine the TMR value decreases with bias of Fe/MgO/Fe MTJ: (1) interfacial states lying at 1.06 eV in spin down channel (2) the energy level of the spin down Δ1 band of the Fe electrode. Our results showed that an inserted Ag mono-layer at Fe/MgO interface can remarkably improve the TMR effect at a high bias voltage.

In Situ Soft X‐ray Microscopy Study of Fe Interconnect Corrosion in Ionic Liquid‐Based Nano‐PEMFC Half‐Cells

AbstractThis in situ soft X‐ray scanning microscopy electrochemical study of model proton exchange cathodic and anodic nano‐fuel cells is exploring the evolving structure and chemical composition of key cell components represented by Au and Fe electrodes in contact with Nafion‐ionic liquid composite electrolyte containing Pt black catalyst particles. Morphological and chemical changes of the electrodes as well as the chemical state and fate of the Fe species released into the electrolyte are monitored in short circuit and with applied cathodic or anodic polarization. The in situ X‐ray absorption images of the cathodic cell fed with 2.5 × 10–5 mbar O2 have revealed corrosion‐induced morphology changes in the Fe electrode, being more pronounced in the vicinity of Pt‐black particles, and deposition of the Fe species released into the electrolyte, onto the intact Au counter electrode upon cathodic polarization. The Fe electrodes of the anodic cell containing NaBH4 in the electrolyte appear relatively more corrosion resistant. The Fe L3 absorption spectra taken in different locations within the Fe electrode have shown lateral variations in the relative ratio between Fe2+ and Fe3&4+ oxidation states, whereas the Fe species released into the RTIL electrolyte are only in the high Fe3&4+ oxidation states.

Decontamination of synthetic textile wastewater by electrochemical processes: energetic and toxicological evaluation

The treatment of a synthetic textile wastewater, prepared with several compounds used in the finishing of textile materials, was comparatively studied by electrochemical methods such as electrooxidation (EO) (titanium electrode) and electrocoagulation (EC) (with aluminum and iron electrodes). The influence of pH, current density and operating time on the treatment was assessed by the parameters used to measure the level of organic contaminants in the wastewater; i.e. color, toxicity and chemical oxygen demand (COD). The experimental results showed that an effective electrochemical oxidation was achieved in which the wastewater was decolorized and 92% of COD was completely eliminated. In particular, the mineralization took place by indirect oxidation, mediated by active chlorine, and the treatment efficiency was enhanced by the addition of NaCl to the wastewater and by increasing the applied current density. The toxicity, still higher than the toxicity of the raw effluent, indicated a presence of toxic products after EO. Good results were obtained with the Al and Fe electrodes, mainly with respect to the removal of color and toxicity. EC is more economical than EO and the toxicity evaluation with the Daphnia magna test shows a significant reduction after EC.

Treatment of Endocrine Disrupting Chemical From Aqueous Solution by Electrocoagulation

The removal of endocrine disrupting chemical (BPA; Bisphenol–A) from aqueous solution was experimentally investigated by electrocoagulation process. The effects of different combinations of aluminum (Al) and iron (Fe) electrode pair, supporting electrolyte type, supporting electrolyte concentration, initial pH and applied current density and initial BPA concentration on the Chemical Oxygen Demand (COD), and energy consumption performances were critically evaluated. The experiment results indicate that Al–Al electrode pair is the most efficient choice of the four electrode pairs. The COD removal efficiency was increased when NaCl was used as the supporting electrolyte instead of Na2SO4 and NaNO3. The optimum supporting electrolyte type and its concentration, initial pH, applied current density and treatment time were found to be NaCl, 0.05 M, pH 7.0, 12 mA cm−2 and 40 min, respectively. Energy consumption was found to decrease with increase of NaCl concentration while it increases with increasing applied current density. The initial and treated sample was characterized by UV–vis spectroscopy to confirm the treatment efficiency. The sludge formed during electrocoagulation was characterized by XRD and SEM/EDAX analysis.

Removal of turbidity, COD and BOD from secondarily treated sewage water by electrolytic treatment

A preliminary study was conducted for the removal of turbidity (TD), chemical oxygen demand (COD) and biochemical oxygen demand (BOD) from secondarily treated sewage (STS) water through the electrolytic batch mode experiments with DC power supply (12 V) up to 30 min and using a novel concept of electrode combinations of different metals. The different surface areas (40, 80, 120 and 160 cm2) of the electrodes as a function of cross-sectional area of the reactor and the effect of inter-electrode distances (2.5–10 cm) on the electrolysis of STS water were studied. This study revealed that the effluent can be effectively treated with the aluminum (Al) and iron (Fe) electrode combinations (Al–Fe and Fe–Al). The maximum removal of TD (81.51 %), COD (74.36 %) and BOD (70.86 %) was recorded with Al–Fe electrode system, while the removal of these parameters was found to be 71.11, 64.95 and 61.87 %, respectively, with Fe–Al electrode combination. The Al–Fe electrode combination had lower electrical energy consumption (2.29 kWh/m3) as compared to Fe–Al electrode combination (2.50 kWh/m3). The economic evaluation of electrodes showed that Al–Fe electrode combination was better than Fe–Al electrode combination. This revealed the superiority of aluminum as a sacrificial electrode over that of iron which can probably be attributed to better flocculation capabilities of aluminum than that of iron.

Single Molecule Magnetoresistance with Combined Antiferromagnetic and Ferromagnetic Electrodes

The magnetoresistance of a hydrogen-phthalocyanine molecule placed on an antiferromagnetic Mn(001) surface and contacted by a ferromagnetic Fe electrode is investigated using density functional theory based transport calculations and low-temperature scanning tunneling microscopy. A large and negative magnetoresistance ratio of ~50% is observed in combination with a high conductance. The effect originates from a lowest unoccupied molecular orbital (LUMO) doublet placed almost in resonance with the Fermi energy. As a consequence, irrespective of the mutual alignment of magnetizations, electron transport is always dominated by resonant transmission of Mn-majority charge carries going through LUMO levels.

Direct Synthesis of ZnO Nanorod Field Emitters on Metal Electrodes

Tapered zinc oxide (ZnO) nanorods have been grown directly on Fe and Cu electrode surfaces using a facile, one-step seedless (catalyst-free) solution processing method. Diaminopropane (DAP) is used to facilitate the growth of tapered nanorods. Fe electrodes remain nearly intact for the duration of synthesis, yielding low areal density ZnO nanorod arrays, while Cu electrodes were continuously etched and grew relatively high areal density arrays with a strong interfacial connection. However, despite the presence of dissolved metal ions within the synthesis solution, Auger analysis reveals dopant-free ZnO nanorods. The fabricated nanorod arrays were demonstrated as a field emission source.

Transport Properties of Fe/GaAs/Ag(001) System

We present results of ab initio transport calculations for epitaxial magnetic tunnel junctions Fe/GaAs/Ag(001). The electronic structure is calculated by means of the tight-binding linear muffin-tin orbital method and the ballistic conductances are evaluated within the Kubo-Landauer formalism which includes the effect of the spin-orbit interaction. Particular attention is paid to the dependence of the conductances on the orientation of magnetization direction of the Fe electrode with respect to the crystal lattice and on the thickness of the tunneling barrier. We have found that the in-plane tunneling anisotropic magnetoresistance (TAMR) exhibits a non-monotonic thickness dependence with a maximum around 7.5 nm of GaAs. This behavior is ascribed to a hybridization of interface resonances formed on both sides of the junction and manifested as hot spots in k[]-resolved conductances. For thicker GaAs barriers, the relative intensity of the hot spots is reduced on account of the contribution from a narrow central region of the two-dimensional Brillouin zone which leads to the final decrease of the TAMR effect.

Effect of operational parameters on the removal of phenol from aqueous solutions by electrocoagulation using Fe and Al electrodes

The removal of phenol from aqueous solutions in a batch electrocoagulation (EC) process using Fe and Al electrodes was investigated. Experiments were carried out to remove phenol by the EC covering a wide range of operating conditions such as initial pH (4–9), current density (20–80 A/m2), initial phenol concentration (20–80 mg/L), conductivity (500–1,500 μS/cm), and operating time (0–100 min). The optimum operating conditions were determined as initial pH 7.0, initial concentration of 50 mg/L, current density of 40 A/m2, operating time of 100 min, and conductivity of 1,200 μS/cm for both electrodes, respectively. The removal efficiencies of phenol at the optimum operating conditions were 98.6% for Fe electrode and 99.2% for Al electrode. The operating cost and consumptions of electrode and energy in the EC process were calculated as 7.4 €/m3, 3.85 kg/m3, and 43.27 kWh/m3 for Fe electrode and 6.1 €/m3, 1.28 kg/m3, and 42.18 kWh/m3 for Al electrode, respectively. The EC process with Al electrode was found to be more efficient than the EC process with Fe electrode in terms of the removal efficiency and operating cost.

Kinetic study of slaughterhouse wastewater treatment by electrocoagulation using Fe electrodes

In this study, treatment of slaughterhouse wastewater by electrocoagulation was investigated in batch system using Fe electrodes. The effect of various variables such as electrode number, current density and operating time was tested. Pollutant removal efficiency increased with increasing electrode number and operating time. The biochemical oxygen demand (BOD(5))(,) chemical oxygen demand (COD), total suspended solid (TSS), and total nitrogen (TN) removal efficiencies using eight electrodes at a contact time of 50 min and a current density of 10 A/m(2) were 66, 62, 60, and 56%, respectively. Higher electrode numbers will allow shorter operating times to achieve certain removal efficiencies. Also, removal efficiencies increased by increasing the current density; the highest removal efficiencies of BOD(5,) COD, TSS, and TN at a contact time of 50 min and a current density of 25 A/m(2) were 97, 93, 81, and 84%, respectively. The results also show that the reactor pH varies directly with the current density; at 25 A/m(2), the reactor pH increased from an initial value of 7.1 to 7.7 after 50 min. The experimental results showed that the kinetics of BOD(5), COD, TSS and TN removal could be fitted adequately using a first order kinetic model (higher R(2)).