Powder Electrodes Research Articles

Synthesis and electrochemical properties of TiO 2/nanodiamond nanocomposite

Undoped nanodiamond (ND) powders were coated with TiO 2 through two steps: firstly Ti lay was deposited by cycled vacuum-feeding chemical vapour deposition from gaseous TiCl 4/H 2, and secondly an oxidation treatment was carried out in air. The structure and the morphology of the TiO 2/ND composite were characterized by Raman spectrum and transmission electron microscopy. The electrochemical properties of the TiO 2/ND powder electrode in a solution containing [Fe(CN) 6] 3−/4 − or NO 2 − were investigated. The results showed that a continuous coating consisting of Ti nanoparticles covered on ND particle after the deposition. The following oxidation at 500 °C resulted in the formation of anatase phase TiO 2 nanoparticles of about 10 nm. The electrochemical results confirmed that the TiO 2/ND powder electrode exhibited higher electrochemical activity than the pristine ND electrode, especially higher catalytic ability toward the oxidation of nitrite anions. Moreover, the TiO 2/ND powder electrode presented fast response towards nitrite oxidation with a detection limit of 0.55 µM and a linear range of 0.05 to 1.0 mM.

Electrochemical properties of xLi2MnO3⋅(1−x)LiMn0.33Ni0.33Co0.33O2 (x

xLi2MnO3⋅(1−x)LiMn0.33Ni0.33Co0.33O2 electrode powders (in which x=0–0.5) were synthesized by the co-precipitation method. Agglomerates of ∼500 nm particles are shown in scanning electron microscopy (SEM) photos. The cyclic voltammogram of xLi2MnO3⋅(1–x)LiMO2 electrode powders clearly shows two peaks at 4.3 V and 4.6, which correspond to the oxidation peaks of LiMO2 and Li2MnO3. In the case of x=0.1, there were no ordering peaks at 20–25° in the x-ray diffraction (XRD) pattern, and the lowest capacity compared with other experimental compositions was observed.

Electrochemical processes on graphite powder electrodes in HNO3 solutions

Nature and kinetics of electrode processes on disperse graphite electrodes were studied in 15–60% HNO3 solutions.

Production of Oxidizing Intermediates during Corrosion of Iron: Implications for Remediation of Contaminants from Mineral and Metal Processing

Elemental iron has a long history of use for reductive recovery of dissolved metals from waters associated with ore bodies, mining and mineral processing activities. It has recently been recognized that Fenton's reagent, which generates powerful oxidants, may be generated when iron corrodes in the presence of oxygen. If the iron is nanoparticulate, enough oxidant may be generated for practical applications. However, there is ample indication in the literature that oxidation reactions on iron at near-neutral pH are strongly sensitive to the source of the iron, which affects the surface. This was investigated here for electrolytic iron powder, and two types of nanoparticulate iron, using a modified packed powder electrode. The behavior of bulk iron was investigated using a rotating disk electrode. The results revealed significant differences in the corrosion behavior of the different iron samples, indicating that these would yield significantly different results if employed for oxidation reactions.

Performance of Difference Electrode Materials in Electrical Discharge Machining of Tungsten Carbide

Problem statement: Electrical Discharge Machining (EDM) is now a well-established machining option in many industries. Tungsten carbide (WC-Co) is an important tool and die material mainly because of its high hardness, strength, wear resistance and high melting point. Normally, EDM is capable of machining geometrically complex or hard material component, that are precise and difficult to machine. The objective of this research is to study the performance of different electrode materials on tungsten carbide workpiece with EDM process. Approach: The electrode materials were graphite (Poco EDM-3), copper-graphite (Poco EDM-C3) and copper-tungsten (solid).The important parameters were discharge current, on time, off time, open-circuit voltage and electrode polarity. A workpiece material was a tungsten carbide (W 90-Co10). Results: The results show that the electrode negative polarity performs very well, Poco EDM-3 gives higher Material Removal Rate (MRR). Both powder electrode (EDM-3 and EDM-C3) give the better MRR and EWR more than solid electrode. Conclusion: The suitable duty factor is 11%. The Surface Roughness (SR) of copper-tungsten give the best when current peak intensity not over 20 amperes.

Mechanism of aerobic visible light formic acid oxidation catalyzed by poly(tri-s-triazine) modified titania

Visible light aerial oxidation of formic acid catalyzed by N/C-modified titania (TiO(2)-N,C) is investigated by wavelength-dependent photocatalytic and photoelectrochemical experiments in the presence of oxygen, tetranitromethane, and methylviologen as electron acceptors. The title reaction is shown to proceed both through oxidative and reductive primary processes. Contrary to the urea-derived (TiO(2)-N,C), so-called "N-doped" titania (TiO(2)-N) as prepared from ammonia is inactive. In accord with photocurrent action spectra of corresponding powder electrodes, this different activity of the two photocatalysts is traced back to the different chemical nature of the reactive holes localized at the modifier. Hole stabilization by delocalization within an extended poly(tri-s-triazine) network of TiO(2)-N,C is proposed to render recombination with conduction band electrons less probable than in TiO(2)-N.

Cyclic Voltammetry of ZrO2 Powder in the Metallic Cavity Electrode in Molten CaCl2

The electrochemical reduction of the insulative powder in molten was investigated using the metallic cavity electrode (MCE) in molten at . Cyclic voltammograms (CVs) revealed two consecutive reduction peaks corresponding to (i) to and (ii) to Zr. The intermediate, , was metastable and underwent disproportionation to and Zr, which was responsible for the detection of Zr metal in the potentiostatic reduction at less negative potentials. In the anodic scan, four main oxidation processes were observed. The relevant reactions were rationalized as the reoxidation of (iii) to , (iv) Zr to , (v) Zr to , and (vi) Zr to . The metastable intermediate also contributed to the unique current variations in the anodic potential scans under different conditions. Potentiostatic electrolysis of the powder in the MCE at the feature potentials of the CVs and analyses of the electrolysis products by scanning electron microscopy and energy dispersive X-ray spectroscopy confirmed the electroreduction mechanism and revealed the localized conversion of the dense aggregates of the submicrometer particles of to cauliflower-like aggregates of the nanoparticulates of Zr in the early stage of the electroreduction process.

Electrochemical characteristics of hydrothermally deposited nickel hydroxide on multi-walled carbon nanotube for supercapacitor electrode

Supercapacitor performance of nickel hydroxide powder electrode with different carbon conductor and nickel hydroxide/multi-walled carbon nanotube composite electrode had been studied by cyclic voltammetic method in 6 M KOH solution. Active carbon, Superp, Ketjen Black and multi-walled carbon nanotube were used as carbon conductor in nickel hydroxide powder electrode. It showed that multi-walled carbon nanotube conductor can bring good performance for nickel hydroxide powder supercapacitor electrode. Moreover, nickel hydroxide/multi-walled carbon nanotube composite was fabricated by hydrothermal method, using as supercapacitor electrode. Our findings show that 10 wt% nickel hydroxide loading on multi-walled carbon nanotube has good power performance. The capacitances for 10 wt% nickel hydroxide loading amount at high scan rate 100 and 500 mV/s were 221 and 118 F/g, respectively. Nickel hydroxide evenly loaded onto multi-walled carbon nanotube composite electrode has good conductivity and can contribute more capacitance.

Thermoelectrochemically Activated MoO2 Powder Electrode for Lithium Secondary Batteries

The high temperature lithiation behavior of the electrode is examined, which is lithiated by one-electron reduction (by addition reaction) at room temperature. At elevated temperatures, this electrode is lithiated with four-electron reduction by addition and continued conversion reaction. As a result of four-electron reduction, the initial crystalline phase is decomposed into a nanosized mixture of metallic Mo and , which is in turn converted to nanosized upon forthcoming delithiation. An interesting feature here is that as-generated nanosized is now fully lithiated up to four-electron reduction even at room temperature. This phenomenon is named “thermoelectrochemical activation” because the extension from one- to four-electron reduction is achieved by a simple charge–discharge cycling made at elevated temperatures. The thermoelectrochemically activated electrode delivers a reversible specific capacity that is close to the theoretical four-electron capacity with an excellent cycle performance at room temperature.

Intermediate temperature single-chamber methane fed SOFC based on Gd doped ceria electrolyte and La0.5Sr0.5CoO3−δ as cathode

Abstract Single-chamber fuel cells with electrodes supported on an electrolyte of gadolinium doped ceria Ce1−xGdxO2−y with x = 0.2 (CGO) 200 μm thickness has been successfully prepared and characterized. The cells were fed directly with a mixture of methane and air. Doped ceria electrolyte supports were prepared from powders obtained by the acetyl-acetonate sol–gel related method. Inks prepared from mixtures of precursor powders of NiO and CGO with different particle sizes and compositions were prepared, analysed and used to obtain optimal porous anodes thick films. Cathodes based on La0.5Sr0.5CoO3 perovskites (LSCO) were also prepared and deposited on the other side of the electrolyte by inks prepared with a mixture of powders of LSCO, CGO and AgO obtained also by sol–gel related techniques. Both electrodes were deposited by dip coating at different thicknesses (20–30 μm) using a commercial resin where the electrode powders were dispersed. Finally, electrical properties were determined in a single-chamber reactor where methane, as fuel, was mixed with synthetic air below the direct combustion limit. Stable density currents were obtained in these experimental conditions. Temperature, composition and flux rate values of the carrier gas were determinants for the optimization of the electrical properties of the fuel cells.

Influence of irreversible reactions at non-graphitizable carbon electrodes on their thermal stability in Li-ion batteries

The thermal stability of four kinds of non-graphitizable carbon negative-electrodes was studied quantitatively by differential scanning calorimetry (DSC). Charged non-graphitizable carbon electrode powder gave exothermic peaks at around 300 °C. The heat values increased with both the charge capacity and the amount of charged electrode powder sealed in a hermetic pan. Based on the present and previous results, the heat values increase with an increase in the charge capacity, the irreversible capacity, and the amount of charged electrode powder. Exothermic peaks were seen at around 290 °C even for discharged non-graphitizable carbon electrode powder. The heat values increased with the irreversible capacity. The amount of Li-ions remaining in the carbon as well as the amount of surface film should increase with the irreversible capacity, and therefore the heat values increased for discharged non-graphitizable carbon.

Electropolymerizing polyaniline on undoped 100 nm diamond powder and its electrochemical characteristics

Conductive polyaniline (PANI) was electropolymerized on undoped 100 nm diamond powders in sulphuric acid solution containing aniline to improve the conductivity and the electrochemistry of the nano- or submicro-scaled diamond particles. Cyclic voltammetry (CV) experiment was carried out at an upper potential of 1.1 V in initial sweeps and a potential range of −0.2–0.9 V for the growth of PANI on a diamond powder electrode. Field emission-scanning electron microscope (FESEM) result reveals that the diamond particles were well coated by PANI films with globular or fibroid surface morphology. Cyclic voltammetry and electrochemical impedance spectroscopy (EIS) were employed to investigate the electrochemical properties of the PANI/diamond composite electrode. It presents lower resistance and better capacitance than the pristine diamond powder.

Novel concept of pseudocapacitor using stabilized lithium metal powder and non-lithiated metal oxide electrodes in organic electrolyte

A concept of using two non-prelithiated metal oxides (e.g., MnO 2, V 2O 5, and FeO x ) in both positive and negative electrodes in organic Li-ion electrolytes has been proposed and tested to improve the energy density of pseudocapacitors. To take the advantages of this concept, additional lithium source is essential to provide lithium ions during the charge–discharge cycles. The stabilized lithium metal powder (SLMP ™) developed by FMC Corp., provides such an essential Li + source. Here we report the first result of the symmetric pseudocapacitor using two non-prelithiated metal oxide (i.e., manganese oxide/carbon nanotube (MnO 2/CNT)) electrodes, with added SLMP in one of them. The capacitor using the SLMP added MnO 2/CNT (positive) and pure MnO 2/CNT (negative) electrode in 1.2 M LiPF 6-EC:EMC electrolyte shows supercapacitive behaviors in 3.0 V voltage range. The addition of SLMP opens new opportunities of using the non-lithiated metal oxide electrodes in pseudocapacitors and hybrid electrochemical capacitors (ECs), which has not been possible before.

Viscoelastic Inks for Direct-Write Microfabrication of Single-Chamber Micro Solid Oxide Fuel Cells with Coplanar Thick Electrodes

AbstractSingle-chamber micro solid oxide fuel cells (SC-μSOFCs) with coplanar electrodes were fabricated using a robotically controlled direct-write microfabrication approach. Viscoelastic, gel-based inks were employed to create homogeneous electrodes of controlled width and interelectrode distance as well as uniform cross-sectional thickness. Electrode powders, NiO-YSZ (yttria-stabilized zirconia) for the anode and (La0.8Sr0.2)0.98MnO3-YSZ for the cathode, were first dispersed with a cationic polyethyleneimine solution. Polyacrylic acid was added to induce a fluid-to-gel transition. The rheology of the fabricated inks was characterized. The inks were then extruded through cylindrical micronozzles and deposited onto YSZ electrolyte substrates using a robotic deposition apparatus. Thickness and width of the sintered electrodes were close to the diameter of the extrusion nozzle. The improved shape retention of the deposited electrodes also enabled the fabrication of continuous electrodes with square cross-section. The cathode adhered very well to the electrolyte during sintering. However, the mismatch between the thermal expansion coefficient of anode and electrolyte seems to cause detaching and breaking of the anode so that electrochemical characterization of the fabricated cells was not yet possible.

Reversible lithium storage in LiF/Ti nanocomposites

Storage and transport behaviors of lithium in LiF/Ti nanocomposites, either formed in situ through a conversion reaction from TiF(3) powder electrode or prepared by the pulse laser deposition method, have been investigated. Reversible lithium storage in the LiF/Ti nanocomposites shows a sloped voltage profile. The lithium storage capacity in the LiF/Ti nanocomposite thin film is much higher than that in single Ti or LiF thin film with the same thickness and is increased with increasing film thickness. Accordingly, lithium should store at the grain boundary regions since either the LiF or the Ti phase is not active for lithium storage. Hence, this type of interfacial storage is intermediate between the insertion and storage in supercapacitors. The transport properties of electrons and lithium ions in initial LiF/Ti nanocomposites are also investigated by IV, IS and blocking electrode techniques.

Thermal stability of the interface between discharged non-graphitizable carbon and electrolyte for lithium-ion batteries

The thermal stability of a non-graphitizable carbon electrode was studied quantitatively by differential scanning calorimetry (DSC). Charged non-graphitizable carbon electrode powder gave exothermic peaks at around 300 °C and the heat values varied depending on the ratio of the electrode powder to coexisting electrolyte solution. Based on the similarities in the exothermic behaviors of charged graphite and non-graphitizable carbon electrodes, the exothermic reactions at around 300 °C should be assigned to the reductive decomposition of a surface film by charged non-graphitizable carbon. On the other hand, non-graphitizable carbon electrode powder showed exothermic reactions at around 290 °C even at a discharged state, while almost no exothermic heat was seen for a discharged graphite electrode powder at temperatures above 250 °C. The heat values decreased as Li-ions in the non-graphitizable carbon electrode were extracted. Based on the present results and a consideration of the slow diffusion and irreversible trapping of Li-ions in non-graphitizable carbon, Li-ions remaining in non-graphitizable carbon could induce exothermic reactions at around 290 °C, even at a discharged state.

Electrochemical Conversion of Oxide Precursors to Consolidated Zr and Zr−2.5Nb Tubes

Porous tubular oxide precursors have been fabricated from the ZrO 2 powder and its mixture with the Nb 2 O 5 powder, and directly metallised to pure Zr or the Zr-2.5Nb Zircaloy tubes through electrochemical reduction and deoxygenation that induces in situ consolidation or sintering of the metallized tubes in molten CaCl 2 at ∼900 °C. This new process is simple, fast, and low in energy consumption, promising a new technology for the fabrication of zirconium/Zircaloy tubes, which are the crucial materials in nuclear reactors and chemical plants. Also reported in this paper is the mechanism of the electrochemical process, correlating the cyclic voltammogram of ZrO 2 powder in a metallic cavity electrode with the morphological and compositional analyses of the products from potentiostatic electrolysis of porous ZrO 2 pellets.

Overpotential and electrochemical impedance analysis on Cr 2O 3 thin film and powder electrode in rechargeable lithium batteries

The overpotentials of Cr 2O 3 thin film and powder electrodes as well as various benchmark anodes and cathodes in rechargeable lithium batteries have been compared by analyzing the galvanostatic voltage profiles. Li-storage in the Cr 2O 3 electrode through the conversion reaction shows higher overpotential values than through other Li-storage mechanisms. The origins of the high overpotential of the Cr 2O 3 electrode have been studied by electrochemical impedance spectroscopy. It is found that the ohmic polarization, charge transfer resistance and diffusion impedance of the Cr 2O 3 electrode decrease significantly with the insertion of lithium and increase with the extraction of lithium. The calculated overpotential contribution from the diffusion impedance is well consistent with the value deduced from the galvanostatic voltage profiles. It means that the sluggish diffusion should be the main origin for high polarization of Cr 2O 3 electrodes.

Bismuth/Glassy Carbon Composite Electrode for the Determination of Trace Lead and Cadmium

We examined the use of a bismuth/glassy carbon (Bi/C) composite electrode for the determination of trace amounts of lead and cadmium. Incorporated bismuth powder in the composite electrode was electrochemically dissolved in 0.1 M acetate buffer (pH 4.5) where nanosized bismuth particles were deposited on the glassy carbon at the reduction potential. The anodic stripping voltammetry on the Bi/C composite electrode exhibited well-defined, sharp and undistorted peaks with a favorable resolution for lead and cadmium. Comparing a non-oxidized Bi/C composite electrode with an in-situ-plated bismuth film electrode, the Bi/C composite electrode exhibited superior performance due to its much larger surface area. The limit of detection was 0.41 μ/L for lead and 0.49 μ/L for cadmium. Based on this study, we are able to conclude that various types of composite electrodes for electroanalytical applications can be developed with a prudent combination of electrode materials.

Structure and Electrochemical Performance of Li[Ni1−x−yCoxMny]O2 [0.025 ≤ x ≤ 0.4, 0.015 ≤ y ≤ 0.25] as Cathodes Compound for Lithium Ion Batteries

Li[Ni(1-x-y)Co(x)Mn(y)]O2 (0.025 < or = x < or = 0.4, 0.015 < or = y < or = 0.25) electrode powders were prepared by a solid-state reaction. The phase purity and R-3m layered structure of the synthesized Li[Ni(1-x-y)Co(x)Mn(y)]O2 materials were confirmed by X-ray diffraction analysis. The particle size of the powder/compounds was decreased with increasing Co and Mn contents to a minimum average particle size of 0.2 approximately 0.3 microm for the LiNi0.35Co0.4Mn0.25O2 powder. A specific capacity of 187 mAh/g was obtained for the LiNi0.35Co0.4Mn0.25O2 electrode with good capacity retention when cycled in the potential region of 3.0-4.6 V with a current density of 20 mA/g at room temperature. Although the structural parameters of the LiNi0.35Co0.4Mn0.25O2 cathode material were similar to those of the LiNil/3CO1/3Mn1/3O2 powder, its specific capacity was higher due to the higher Co contents.