Magnetite Electrode Research Articles

Electrochemical characterization of binder effect in natural magnetite electrodes for fluoride removal of well water

This work presents the study of the behavior of magnetite in fluoride electroadsorption. A concern in the fluoride electroadsorption is related to the type of binder, fluoride concentration, pH, and coexisting ions. A graphite/Nafion/magnetite electrode increases the specific capacitance of the surface favoring the surface complexation of anions due to the increase in the effective adsorption surface in this system. There is a tendency to increase the specific capacitance when the concentration and pH increase. The anionic affinity of the system is directly related to the nature of the ions and the hydrated ionic radius, in ions with the same charge, a lower hydrated radius results in a greater possibility of surface complexation. Excess OH− groups increase the accumulation of charge in the double layer, making the surface complexation of the anionic species towards the surface difficult. The selectivity trend is: CO32− > SO42− > F− > Cl− > NO3−.

Construction of conductive network using magnetite to enhance microflora interaction and petroleum hydrocarbons removal in plant-rhizosphere microbial electrochemical system

The combined bioremediation of microorganisms and plant roots is an environmentally friendly soil remediation technology with the application prospect. The inefficiency of electron transfer hinders the decomposition of reluctant petroleum hydrocarbons and the further absorption by plant roots in plant-rhizosphere microbial electrochemical system. A conductive network of extracellular electron transfer was constructed in this study by the combination of magnetite and external electrode, committed to strengthening the process of Direct interspecific electron transfer (DIET), Dissimilation iron reduction (DIR), and long-distance electron transport. The microbial conversions of C, N, and Fe related to the hydrocarbon removal were investigated in the compound remediation system (Fe + MEC). Compared with the control group (PCK), an increased 174–232% of Total petroleum hydrocarbons (TPHs) was removed from Fe + MEC, accompanied by the generation of bio-current. Synchronously, the reduction of iron oxide (mainly DIR) and nitrogen (mainly denitrification) was promoted due to the rapid transfer of extracellular electrons. A reinforced synergistic network of the potential degradation, denitrification, and iron-reducing/exoelectrogenic bacteria was constructed in the compound system, which may be connected through the magnetite-mediated electron transport chain. The results in this study provide an insight into the impasse overcoming of inefficient electron transfer during the remediation of organic contaminated soil.

Preparation of self-assembled porous flower-like nanostructured magnetite (Fe3O4) electrode material for supercapacitor application

Preparation of self-assembled porous flower-like nanostructured magnetite (Fe3O4) electrode material for supercapacitor application

X-ray fluorescence mapping: Insights into mesoscale structure impact on battery functional electrochemistry

Electron transfer and ion transport occurs over multiple-length scales ranging from the atomic to mesoscale within battery materials and electrodes. Micro-X-ray fluorescence (µ-XRF) is an important characterization tool as it can resolve structural, compositional, and redox information while providing insight into the spatial distribution of an electroactive material. In this work, µ-XRF mapping is used to probe the distribution of iron within thin planar slurry-based and thick porous carbon nanotube (CNT)-based magnetite (Fe3O4) electrodes. Notably, the porous CNT-based electrode showed homogenous distribution of Fe within the electrode whereas the planar electrode demonstrated distinct Fe aggregates. This information was used to rationalize the electrochemistry observed by cyclic voltammetry and galvanostatic cycling. The thick porous electrode delivered 215% more capacity per gram of magnetite during the first discharge, consistent with increased electrode homogeneity enabling effective ion access and electron transfer.Graphical

Insight into the charging–discharging of magnetite electrodes: in situ XAS study

Insight into the charging–discharging of magnetite electrodes: <i>in situ</i> XAS study

Electrochemical Sensor Based on Reduced Graphene Oxide Incorporated with Magnetite and Silver Nanoparticles Composite Electrode for Determination of Dopamine

Dopamine determination has become crucial as the abnormal levels of dopamine can potentially cause psychological disorders as well as Parkinson’s disease. Herein, a novel electrochemical sensing platform based on magnetite (Fe3O4), silver nanoparticles (AgNPs) and reduced graphene oxide (rGO) composite, denoted as rGO-Fe3O4/AgNPs was facilely synthesized using a modified Hummer’s two-step synthesis and co-precipitation approach without the use of any other oxidants or stabilizers. This composite was designed as an electrochemical sensor for exceptionally sensitive DA detection in human urine samples. The microscopic study of the composite revealed that the Fe3O4 and AgNPs were extensively decorated onto the rGO surface. The optimized scan rate of 100 mV s−1 and neutral pH of the supporting electrolyte for the composite-modified electrode was further used to determine dopamine (DA) in human urine samples. DA displayed an anodic peak at 0.20 V vs Ag/AgCl (3.0 mol l−1 KCl) utilizing differential pulse voltammetry technique. With detection limits of 3.98 nM, the analytical curves obtain a wide range of linear from 0.015 μM to 100 μM. The designed sensor had several advantages, including ease of preparation, low cost of nanomaterials utilized, and rapid response.

Insight into the charging-discharging of magnetite electrodes: in situ XAS and DFT study.

The structural changes of Fe3O4 nanoparticle electrodes in Li ion batteries during charging-discharging cycles have been investigated using in situ X-ray absorption spectroscopy (XAS). Chemometric methods viz., Principal Component Analysis (PCA) and Multivariate Curve Resolution-Alternate Least Square (MCR-ALS) have been used for analysis of the in situ XANES data during the charge-discharge cycle, which help to identify the various species formed during the lithiation-delithiation of Fe3O4. The concentration variation of the different species has also been determined and the detailed intercalation-conversion mechanism of the Fe3O4 electrodes during the first discharge has been established. Subsequently, the first charge and second discharge cycles were also studied to apprehend the difference in redox reaction between the first discharge and subsequent cycles. The above studies clearly identify the four species involved in the whole intercalation-conversion process of Fe3O4 electrode of a Li ion battery and also indicate the irreversibility of the conversion reaction in subsequent cycles which may be one of the reasons for capacity fading of these electrodes. The above results have also been corroborated with density functional theory (DFT)based ab inito calculations.

Temporally and Spatially Resolved Visualization of Electrochemical Conversion: Monitoring Phase Distribution During Lithiation of Magnetite (Fe3O4) Electrodes

Fundamental understanding of transport properties across multiple size regimes is critical for the rational design of electrodes with conversion materials. While recent studies have effectively int...

The Effect of Stoichiometry of Iron (II) and (III) and Magnetite Oxides on the Kinetic Regularities of their Dissolution in Orthophosphoric Acid Containing Fe (II) and Fe (III) Ions

The kinetics of dissolution of iron oxides FeO, α-Fe2O3 and Fe3O4 in orthophosphoric acid, including those containing additions of Fe (II) and Fe (III) ions (in the form of perchlorates), has been studied. The values of the stationary potential in the magnetite electrode system--solutions of orthophosphoric acid, including those containing additions of Fe (II) and Fe (III) ions are determined. The dissolution of Fe3O4 in orthophosphoric acid has been studied and described. Based on the experimental results, it was established that the stimulating and inhibitory effect of Fe (II) and Fe (III) ions is related to their effect on the value of the potential at the boundary of the iron oxide phases/electrolyte solution. The orders of reactions for ions Fe (II), Fe (III) and H3PO4 are determined

The Factors Determining Charge Rate of Magnetite Electrode and the Functional Mechanism of Sulfide on the Reaction

The electro-reduction of magnetite is important for many different industries. For example, it relates to the extraction of iron from iron ore and the charging of iron-based batteries. The sluggish electro-reduction reaction of magnetite affects the energy efficiency of iron extraction or the charge rate of iron-based batteries. However, what factors affecting the reduction rate is not well understood. In this study, electrochemical analysis, XRD, SEM, EDS mapping and XPS techniques are adopted to analyze the reaction, and it is proved that two factors determine the electro-reduction rate of magnetite electrode: O2− diffusion inside the particles determines the electro-reduction rate of a single particle, and the electrical resistivity of electrode determines how many magnetite particles are involved in electro-reduction simultaneously. Contact resistance between particles is the dominant part of the electrical resistance of the magnetite electrode. The function mechanism of sulfide in the reaction is also revealed: a sulfide additive can react with magnetite to form amorphous or crystal FeS at different potentials. These compounds, especially crystal FeS, coat onto the surface of magnetite particles, and bond them together. The coating and bonding can decrease contact resistance significantly, thus enhancing the electro-reduction rate of magnetite to one order of magnitude.

Galvanic corrosion of carbon steel in anoxic conditions at 80 °C associated with a heterogeneous magnetite (Fe3O4)/mackinawite (FeS) layer

Anodic polarization of carbon steel electrodes in deaerated 0.01molL−1 NaCl+0.01molL−1 NaHCO3+0.001/0.01molL−1 Na2S solutions (with pH∼7.5) led to heterogeneous layers made of magnetite and mackinawite. A locally accelerated dissolution of the steel was observed in any case and the most corroded areas were covered with a layer enriched with mackinawite. This suggests that part of the electrode surface was blocked, covered with a magnetite rich layer where water reduction was favored. The effects of the galvanic coupling between a magnetite electrode and a bare carbon steel electrode covered with a ∼5mm thick argillites layer were then studied in a 0.01molL−1 NaCl+0.01molL−1 NaHCO3 solution at room temperature and 80°C. Electrochemical measurements demonstrated that a relatively high galvanic current initially flowed between the magnetite electrode (cathode) and the steel electrode (anode). However, this current decreased with time down to negligible values. Micro-Raman spectroscopy analysis revealed that a magnetite layer was formed on the steel electrode, thus suppressing the initial difference between anode and cathode. When the same experiment was performed with the steel electrode set under an argillites layer enriched with Na2S, the galvanic current density remained constant at a significant value (∼20μAcm−2) during the 11days of experiment. It led to the formation of a layer composed of mackinawite (and chukanovite) on the steel electrode. This result confirms that heterogeneous magnetite/mackinawite layers can favor galvanic corrosion even in anoxic conditions.

Understanding the Role of Particulate Iron in Lead Release to Drinking Water.

Lead service lines (LSLs) are a major source of drinking water lead, and high iron levels are frequently observed along with elevated lead release. A model distribution system, dosed with orthophosphate, was used to evaluate the effect of corroded iron distribution mains on lead release from recovered LSLs. Lead release was higher by 96 μg L(-1), on average, from LSLs supplied by corroded iron compared to the inert reference material (PVC). This effect may be explained by deposition of semiconducting iron oxide particles within LSLs. When galvanic cells with lead and magnetite (Fe3O4) electrodes were short-circuited, lead release increased 8-fold and a current averaging 26 μA was observed. In effluent from LSLs with an upstream iron main, colloidal lead and iron occurred in the same size fraction-possibly due to release of colloidal particles from LSL corrosion scale enriched with iron. Under these circumstances, high molecular weight (>669 kDa) (208)Pb and (56)Fe elution profiles, observed via size-exclusion chromatography, were highly correlated (average R(2) = 0.97). Increasing orthophosphate from 0.5 to 1.0 mg L(-1) (as PO4(3-)) accompanied an average reduction in lead release of 6 μg L(-1) month(-1) but did not significantly reduce the effect of an upstream iron main.

Preparation, physicochemical, and electrochemical properties of magnetite electrodes for methanol electrocatalytic oxidation in an alkaline medium

Iron oxide nanoparticles are novel functional materials applicable in catalysis. Herein, the proposed method involved synthesis of electrocatalyst iron oxide nanoparticles and their application in oxidation process of methanol. The iron oxide nanoparticles prepared using co-precipitation chemical method, in which ferric and ferrous ions were mixed in a 1:2M ratio in highly basic solutions. The electrocatalyst Fe3O4 further applied for methanol oxidation reaction (MOR) in 0.5M KOH solution at room temperature. MOR was performed on cyclic voltammeter (CV) also measured polarization of process. The methanol oxidation on cyclic voltammetry expressed forward and backward oxidation peak with function of currents at 0.7 and 0.5 V. The prepared Fe3O4 nanoparticles showed significant magnetic property measured by a vibration magnetometer at 300 K. Also, the structure and surface morphology of the catalyst were characterized using X-ray diffraction and environmental scanning electron microscopy (ESEM)–energy dispersive spectroscopy, respectively. ESEM was used to determine Fe3O4 particle size and a high degree of nanoparticle dispersion in oxidation system.

Mesoscale Transport in Magnetite Electrodes for Lithium-Ion Batteries

The mass transport processes occurring within magnetite electrodes during discharge and voltage recovery are investigated using a combined experimental and modeling approach. Voltage recovery data are analyzed through a comparison of the mass transport time-constants associated with different length-scales within the electrode. The long voltage recovery times can be hypothesized to result from the relaxation of concentration profiles on the mesoscale, which consists of the agglomerate and crystallite length-scales. The hypothesis was tested through the development of a multi-scale mathematical model, which showed good agreement with experimental data.

2D Cross Sectional Analysis and Associated Electrochemistry of Composite Electrodes Containing Dispersed Agglomerates of Nanocrystalline Magnetite, Fe₃O₄.

When electroactive nanomaterials are fully incorporated into an electrode structure, characterization of the crystallite sizes, agglomerate sizes, and dispersion of the electroactive materials can lend insight into the complex electrochemistry associated with composite electrodes. In this study, composite magnetite electrodes were sectioned using ultramicrotome techniques, which facilitated the direct observation of crystallites and agglomerates of magnetite (Fe3O4) as well as their dispersal patterns in large representative sections of electrode, via 2D cross sectional analysis by Transmission Electron Microscopy (TEM). Further, the electrochemistry of these electrodes were recorded, and Transmission X-ray Microscopy (TXM) was used to determine the distribution of oxidation states of the reduced magnetite. Unexpectedly, while two crystallite sizes of magnetite were employed in the production of the composite electrodes, the magnetite agglomerate sizes and degrees of dispersion in the two composite electrodes were similar to each other. This observation illustrates the necessity for careful characterization of composite electrodes, in order to understand the effects of crystallite size, agglomerate size, and level of dispersion on electrochemistry.

Capacitance of Fe3O4/rGO nanocomposites in an aqueous hybrid electrochemical storage device

Hybrid electrochemical storage devices comprising a capacitor-type positive electrode and a battery-type negative electrode are regarded as a promising concept combining high power density with high energy density. In this work Fe3O4/reduced graphene oxide (rGO) nanocomposite has been synthesized and applied as negative electrode in an electrochemical energy storage device being a serial internal hybrid of an alkaline battery and an electrochemical double layer capacitor (EDLC). Beneficial effect of graphene on the performance of magnetite electrode has been evidenced by means of cyclic voltammetry, galvanostatic cycling and electrochemical impedance spectroscopy techniques. Unlike in a vast majority of reports, magnetite capacitances have been determined in real electrochemical devices, against activated carbon as positive electrode. In three-electrode cells with activated carbon as the positive electrode magnetite has been found to exhibit from 65 to 83 F g−1 for the rGO content from 9.7 to 27.8 %. The maximum voltage of a capacitor with Fe3O4/rGO negative electrode has been established as 1.0 V, which is higher than typical value of 0.8 V known for the symmetrical carbon-based capacitors.

Electrochemical and Spectroscopic Evidence on the One-Electron Reduction of U(VI) to U(V) on Magnetite

Reduction of U(VI) to U(IV) on mineral surfaces is often considered a one-step two-electron process. However, stabilized U(V), with no evidence of U(IV), found in recent studies indicates U(VI) can undergo a one-electron reduction to U(V) without further progression to U(IV). We investigated reduction pathways of uranium by reducing U(VI) electrochemically on a magnetite electrode at pH 3.4. Cyclic voltammetry confirms the one-electron reduction of U(VI) to U(V). Formation of nanosize uranium precipitates on the magnetite surface at reducing potentials and dissolution of the solids at oxidizing potentials are observed by in situ electrochemical atomic force microscopy. XPS analysis of the magnetite electrodes polarized in uranium solutions at voltages from -0.1 to -0.9 V (E(0)(U(VI)/U(V))= -0.135 V vs Ag/AgCl) show the presence of only U(V) and U(VI). The sample with the highest U(V)/U(VI) ratio was prepared at -0.7 V, where the longest average U-O(axial) distance of 2.05 ± 0.01 Å was evident in the same sample revealed by extended X-ray absorption fine structure analysis. The results demonstrate that the electrochemical reduction of U(VI) on magnetite only yields U(V), even at a potential of -0.9 V, which favors the one-electron reduction mechanism. U(V) does not disproportionate but stabilizes on magnetite through precipitation of mixed-valence state U(V)/U(VI) solids.

마그네타이트 (Fe3O4) 전극의 제조와 전기화학 특성

Flow Accelerated Corrosion (FAC) causes unexpected accidents in a secondary side of a nuclear power plant. The secondary side pipes are mainly carbon steel tubes that have a protective magnetite (Fe3O4) layer on the inner surface. The stability of the protective magnetite layer depends on the parameters related to the FAC phenomena such as pH, temperature, flow rate, surface roughness etc. The dissolution of magnetite is basically the electrochemical reaction, but the most of the experiments of magnetite dissolution were carried out thermodynamically to determine the solubility of magnetite. The knowledge of the electrochemical properties of magnetite is required to understand the dissolution process of magnetite. This paper reviews the manufacture of the magnetite (Fe3O4) electrode, and summaries the electrochemical properties of the magnetite.

Uranium reduction on magnetite: Probing for pentavalent uranium using electrochemical methods

Pentavalent uranium is generally treated as an unstable intermediate when uranyl, U(VI)O22+, is reduced to U4+. However, mineral surfaces have been shown to stabilize pentavalent uranium, thus hindering further reduction (Ilton et al., 2005, 2010). The subject of this study is to identify the kinetic pathways that lead to U(V)O2+ being a metastable species. Electrochemical methods provide an in situ approach for the investigation of the intermediate reaction of U(V)O2+ on the surfaces of magnetite. Redox reactions of uranyl ions on particulate (∼3μm) and bulk magnetite surfaces were investigated using cyclic voltammetry and potential step chronoamperometry using cavity microelectrodes and bulk (planar) mineral electrodes. The estimated redox potentials are consistent with the standard redox potential of UO22+/UO2+, indicating UO22+ is first reduced to UO2+ on the surfaces of both powder and bulk magnetite. The one-electron reduction of UO22+ to UO2+ was further confirmed by directly measuring the number of electrons transferred during the reduction process on the bulk magnetite electrode. Based on the charge conservation analysis and the positive correlation between the pH and the peak current for the UO2+ transformation to UO22+, the peak corresponding to the oxidation of U4+ to UO22+ was assigned in the voltammograms of particulate magnetite. The presence of U4+ indicates that the disproportionation of UO2+ (2U(V)↔U(IV)+U(VI)) is occurring on the surface of particulate magnetite within the timeframe of the experiment. The lack of a peak for U4+ in voltammograms for bulk magnetite suggests that the rate of the UO2+ disproportionation reaction is slower on bulk magnetite than that on particulate magnetite. The catalytic property of particulate magnetite surfaces on the disproportionation reaction is explained by its ability to adsorb and desorb protons, which could facilitate the proton-coupled disproportionation reaction of UO2+. This increased catalytic activity and related adsorption and desorption kinetics of protons may be related to the increased number of under-coordinated surface sites near step edges on the magnetite powder.

Electrochemical Investigation of Gold Uptake From Chloride Solution by Magnetite

An electrochemical method (potential sweep method) was utilized to investigate the nature of the absorbed gold on magnetite and to determine the gold sorption mechanism. A magnetite electrode was prepared in the laboratory, made in contact with a gold chloride solution at different conditions, and was subjected to cyclic voltammetry. The cyclic voltammogram of the magnetite electrode pretreated in a gold chloride solution recorded an anodic current peak at around 1.0 V (vs. Ag/AgCl), which corresponds to the current generated for the anodic dissolution of metallic gold in a chloride medium. The results of the electrochemical experiments suggest that gold chloride complexes are reduced to metallic gold on the surface of magnetite. A four-stage gold uptake mechanism was proposed: (i) the transport of from the bulk solution to the magnetite surface, (ii) adsorption of ions on magnetite surface by electrostatic attraction, (iii) electrochemical reduction of to metallic Au, and (iv) the transport of soluble species to the solution phase. The electrochemical investigation also revealed that Fe3+ ions released from magnetite into the solution, suppressed the gold uptake at the acidic pH region.