Main Electrode Research Articles

Investigation of H2, CO and Syngas Electrochemical Performance Using Ni/YSZ Pattern Anodes

In this work, Ni/YSZ pattern anodes with well-defined 2-D structure were employed to investigate the electrochemical oxidation of H2, CO and syngas. Electrochemical tests revealed that polarization resistance (Rp) depended on applied overpotenital and gas compositions. In H2/H2O environment, Rp decreases when increasing overpotential, H2 and H2O partial pressure. In CO/CO2 environment, Rp experiences a minimum value when increasing the overpotential from 0 to 0.3 V, and the minimum Rp appears when the overpotential is 0.1 V. Rp decreases with an increase in partial pressure of CO2, but increases when increasing partial pressure of CO. Charge transfer reactions contribute to the main electrode process in both H2/H2O and CO/CO2 environments.

100 Millimeters Sphere-Gap with Non Uniform Field Electrodes Triggered Gaps

A common field distortion triggered spark gap utilizing geometric field enhancement at sharp edges usury operates in a cascade mode via the trigger electrode. A new trigger concept is propos this research allowing strong non-uniform electric field enhancement with output precision voltage by holding-off DC voltage ranging from 1 to 135 kV and direct breakdown between the two main electrodes. A test setup was designed to testing with four modes of operation as mode A, B, C and D to prove the feasibility on this concept. Were result experimental r the recommended mode of operation is mode A and mode D considered to be unsatisfied to most applications. The best results achieved by using the triggering with mode A at a wide precision designed breakdown voltage range 1-120kV with a minimum percentage ratio of Fire/Self-fire Voltage lower to 36-47%

Experimental Study of Flat Format Multichannel Triggered Rail Spark Gap

This paper is concerned with the development and testing of a compact flat format multichannel electrically triggered rail spark gap. It is tested for multichannel discharge under atmosphere for high reliability. Multichannel discharge rail spark gaps can be developed using laser trigger or fast rising trigger voltage pulse . The extra volume and weight added by laser or fast triggering circuits limit the use in pulse power applications. An electrically multitriggered low-inductance spark gap is developed. It is used as a multichannel low-inductance discharging element in a fast rising high-current generation system. The trigger of such rail gap is realized using the set of round copper pins similar to single trigger pin in a field distortion spark gap. In parenthesis, five different trigger pins are located in main trigger plate and these are isolated with high impedance. Therefore, five different trigger signals are generated with time difference of tens of nanoseconds. The major material erosion at five points of both stainless steel main electrodes confirms the multichanneling discharge. The main gap spacing in this switch is 4 mm and the trigger is located close to the ground electrode for reducing the delay time and jitter in delay time. This paper shows the trigger circuit design, main gap voltage, and trigger voltage effect on the closing of the spark gap and picture of electrodes after use.

Double-electrode arc welding process: Principle, variants, control and developments

Double-electrode gas metal arc welding (DE-GMAW) is a novel welding process in which a second electrode, non-consumable or consumable, is added to bypass part of the wire current. The bypass current reduces the heat input in non-consumable DE-GMAW or increases the deposition rate in consumable DE-GMAW. The fixed correlation of the heat input with the deposition in conventional GMAW and its variants is thus changed and becomes controllable. At the University of Kentucky, DE-GMAW has been tested/developed by adding a plasma arc welding torch, a GTAW (gas tungsten arc welding) torch, a pair of GTAW torches, and a GMAW torch. Steels and aluminum alloys are welded and the system is powered by one or multiple power supplies with appropriate control methods. The metal transfer has been studied at the University of Kentucky and Shandong University resulting in the desirable spray transfer be obtained with less than 100A base current for 1.2mm diameter steel wire. At Lanzhou University of Technology, pulsed DE-GMAW has been successfully developed to join aluminum/magnesium to steel. At the Adaptive Intelligent Systems LLC, DE-GMAW principle has been applied to the submerged arc welding (SAW) and the embedded control systems needed for industrial applications have been developed. The DE-SAW resulted in 1/3 reduction in heat input for a shipbuilding application and the weld penetration depth was successfully feedback controlled. In addition, the bypass concept is extended to the GTAW resulting in the arcing-wire GTAW which adds a second arc established between the tungsten and filler to the existing gas tungsten arc. The DE-GMAW is extended to double-electrode arc welding (DE-AW) where the main electrode may not necessarily to be consumable. Recently, the Beijing University of Technology systematically studied the metal transfer in the arcing-wire GTAW and found that the desired metal transfer modes may always be obtained from the given wire feed speed by adjusting the wire current and wire position/orientation appropriately. A variety of DE-AW processes are thus available to suit for different applications, using existing arc welding equipment.

Advancements in OCV Measurement and Analysis for Lithium-Ion Batteries

Incremental open-circuit voltage (OCV) curves and low-current charge/discharge voltage profiles of a lithium-ion (Li-ion) battery are compared and evaluated for optimizing measurement time and resolution. Since these curves are often used for further analysis, minimizing kinetic contributions is crucial for approximating battery OCV behavior. In this context, an incremental OCV measurement is characterized by state of charge (SOC) intervals and relaxation times. Various constant low C-rates, SOC intervals, and relaxation times are tested for approximating OCV behavior. Differential capacity and voltage analysis is used to check whether the main electrode features can be resolved satisfactorily. An interpolation method yields additional data points for the differential analysis of incremental OCV curves. It is shown that incremental OCV measurements are suitable for an approximation of battery OCV behavior, rather than low current-voltage profiles. Furthermore, extrapolation of voltage relaxation enables the estimation of fully relaxed OCV.

Design, Simulation, and Characterization of a Low-Cost In-Plane Spark Gap Microswitch With Dual-Trigger Electrode for Pulsed Power Applications

An in-plane spark gap switch with dual-trigger electrode for pulsed power application has been designed and fabricated based on surface micromachining technology. The switch consists of two main electrodes and a dual-trigger electrode to achieve high peak current and smaller trigger voltage. The simulation result shows that 100-V trigger voltage could break down 30-μm distance and then start up the switch. The main discharge channel length has been set as 800 μm to get the optimized output of rise time combined with peak current. The prototype microswitch has been fabricated and characterized. The peak and rising edge of the discharge current are 3450.75 A and 164 ns, respectively, which well agree with simulation values.

Li2NiO2 as a sacrificing positive additive for lithium-ion batteries

This work addresses the electrochemical performances of an over-lithiated lithium nickel oxide (Li2NiO2) as a sacrificing positive additive for lithium-ion batteries. Li2NiO2 decomposes along with a crystalline to amorphous phase transition at 3.5V (vs. Li/Li+) in the first charging period, which is far below the charging potential of common positive electrodes (for instance, ca. 4.0V for LiCoO2). The decomposed amorphous phases then deliver a de-lithiation capacity up to >300mAhg−1 in the first charging. The combined feature of easy decomposition and large first de-lithiation capacity demonstrates that Li2NiO2 is a promising positive additive to provide the electric charges/Li+ ions for the charge compensation on negative electrodes. In addition, this over-lithiated lithium nickel oxide delivers a reversible capacity amounting to 70–90mAhg−1 in the continuing cycles, which is an extra capacity to be added to that delivered by main positive electrodes. It is found that the capacity gain (extra capacity) is larger when Li2NiO2 is decomposed at a faster rate due to a smaller charge transfer resistance. This finding suggests that, when Li2NiO2 is used as the sacrificing positive additive, the use of higher current in the first charging is preferred for the capacity gain.

Fabrication and Testing of Metal Foil Planar Switch

Abstract A metal foil spark gap switch is fabricated by using the magnetron sputtering deposition technology and the standard microelectronic technology. The switch consists of two main electrodes and a trigger electrode. Stylus profiler is used to measure the distance between the main electrode and the trigger electrode. The discharge characteristics of the metal foil spark gap switch are discussed. The switch has short delay time and low time jitter. When it is fired by a conventional capacitive discharge unit (CDU), the firing circuit has low inductance and resistance. Because of its low profile structure, it can be easily integrated with the bridge foil used in a conventional exploding foil initiator system (EFIS).

Model Tests of Electrical Compensation Method for the New Calculable Cross-Capacitor at NIM

In a cross-capacitor with guard electrodes, the equivalent electrical length is sensitive to any variation in the cross section of the main electrodes unless measures are taken to compensate for this. The problem arises particularly in the case of a movable guard electrode, which is conventionally fitted with a nosepiece of such geometry as to compensate for variations in the geometry of the main electrodes from one guard position to another. In the new National Institute of Metrology cross-capacitor, an alternative approach, in which a fraction of the measuring voltage is applied to an isolated electrode in the face of the guard electrode, has been investigated. Results indicate that this modified active compensatory electrode performs as well as or better than an equivalent geometrical compensating nosepiece.

Metal hydrides for high-power batteries

Abstract

Electrostatic injection kicker for the KEK digital accelerator

An electrostatic injection kicker (ES-Kicker) has been developed and installed in the KEK digital accelerator, which is a synchrotron aimed at accelerating all ion species. The ES-Kicker kicks an injected ion beam horizontally into the ring orbit and consists of two main electrodes for electric field generation and three intermediate electrodes to correct field homogeneity. In our single-turn injection scheme, the circulating beam and the injected beam both pass through the electrode aperture of the kicker, so the kicker field must be turned off before arrival of the first circulating beam. The ES-Kicker is therefore operated in a pulse mode. This means that the excitation circuit for the ES-Kicker must be carefully designed, since the falling edge of the electric field is strongly affected by parasitic capacitance of this circuit, and any remaining field may disturb the circulating beam. This paper describes performance of the ES-Kicker on the basis of simulations and measurement results.

Effects of local gas diffusion layer gas permeability variations on spatial proton exchange membrane fuel cells performance

The effects of local gas diffusion layer (GDL) gas permeability variation and its location on spatial and overall proton exchange membrane fuel cell (PEMFC) performance were studied using a segmented cell approach. Variations in the physical and chemical parameters of the main membrane electrode assembly's (MEA) components (e.g., the membrane, electrode, and GDL) are considered defects and might negatively affect fuel cell performance. An artificial GDL defect was introduced by exchanging a standard (or intact) cathode GDL at one segment (segment 4 or 9) with a defective GDL. The standard and defective cathode GDLs had different through-plane gas permeabilities, while values were similar for in-plane permeability and some other structural parameters. The effects from a defective GDL were observed at a high current. Introducing a highly permeable GDL as a defect increased local performance due to a decrease in mass-transfer overpotential. For a defective GDL with lower permeability than the standard GDL, a local performance decrease was observed because mass-transfer losses increased. Simultaneously, downstream segment performance improved, which might be due to changes in water management. Defect localization at the cell outlet resulted in the detection of the defect at a lower current density compared with localization at the cell inlet. Spatial polarization curves (VI) and electrochemical impedance spectroscopy (EIS) facilitated detection and localization of GDL defects. Thus it was demonstrated that the local GDL anomalies are detectable by the segmented cell system.

Role of the Yb3+ concentration in the high efficient UV-blue up-conversion emission from hydrothermally grown Yb3+/Er3+-doped K2YF5 crystals

High intense UV–VIS up-conversion luminescence from orthorhombic K2YF5 fluoride crystals doubly doped with Yb3+ and Er3+ has been obtained under near-infrared excitation at 980nm. Fluoride crystals containing high Yb3+ concentrations, namely 20; 40 and 99at.%, and low Er3+ concentrations have been synthesized under hydrothermal conditions. The role of the Yb3+ ions in the mechanism of the up-conversion process is clearly disclosed with absorption and up-conversion luminescence spectra from which one can see that high intense green (520–545nm) and outstanding UV-blue (380–410nm) emissions are greatly enhanced by increasing the concentration of Yb3+ ions whose aggregate acts as an infrared collector harvesting long wavelength infrared photons. Outstanding total infrared to UV–VIS up-conversion efficiency of 66% has been calculated for the sample with the highest Yb3+ doping level, i.e. 99at.%. These strong UV-blue up-conversion emissions would have the potential use in enhancing spectral response of main semiconductor electrodes (such as TiO2 and Fe2O3), and these K2YbF5 crystals doped with Er3+ could be used in photo-electrochemical devices for sustainable production of hydrogen via photolysis of water, as a promising photonic approach which is currently discussed in the literature.

Metal foil gap switch and its electrical properties

In order to reduce the volume of exploding initiator system, a metal foil spark gap switch was designed and fabricated using magnetron sputter deposition and standard microelectronic technology. The switch constitutes of two main electrodes and a trigger electrode, and stylus profiler was employed to ascertain dimension of the switch. We discussed the discharge characterization of the metal foil spark gap switch under nitrogen atmosphere and at pressure of 0.5 bars, 0.75 bars, 1.0 bar, 1.25 bars, 1.5 bars, and 1.75 bars, respectively. The relationship between self-breakdown voltage of the switch and pressure times distance corresponds to linearity. The switch had short delay time and low time jitter when the operating voltage was between 70% and 90% of its self-breakdown voltage. Compared with a commercial stereo spark gap switch, when it was fired by a conventional capacitive discharge unit, the firing circuit had lower inductance and higher resistance.

ホットワイヤを用いたCO<sub>2</sub>ガスシールドアーク溶接金属部の微細組織とその機械的性質に及ぼす効果

New welding method (F-MAG) based on CO2 gas-shielded arc welding method (MAG) was developed to increase deposition rate of weld metal. In F-MAG, filler wire (hot-wire) heated using direct-current was put into rear part of weld-pool formed with main electrode used in MAG.Multi-layered weld metals were prepared using both F-MAG and MAG. Microstructures of both as-weld and reheated zones in uppermost layer of the multi-layered weld metals were examined and the effects of microstructures on mechanical properties were analyzed. Both the as-weld and reheated zones of weld metal formed with F-MAG consisted of acicular ferrite (AF) and/or equiaxed ferrite and so on. Both strength and elongation in as-weld and reheated zones formed with F-MAG were superior compared with those formed with MAG. It could be suggested that strength increased by refinement of AF due to increase in the concentration of alloy elements being contained in hot-wire. Larger elongation of weld metal in F-MAG compared with that in MAG could be analyzed in terms of the aggregate of AFs with almost parallel slip systems between neighboring AFs, hereafter referred as to ALPS. The number of AFs contained in an ALPS formed in weld metal formed with F-MAG is larger than that with MAG, in spite of the sizes of ALPSs in weld metals formed with MAG and F-MAG being almost same between them. Deformation occurs over a lot of AFs in the case of finer AF through the rotation of tensile test piece during deformation.

Turning into the blue: materials for enhancing TiO2 photocatalysis by up-conversion photonics

We have explored the emerging and ground-breaking photonics approach to enhance the photocatalytic activity of one of the main semiconductor electrodes used in water-splitting reactions, titanium dioxide (TiO2): the blue shifting of the incident radiation by means of a highly efficient up-conversion by a rare-earth (RE) doped luminescent material to assist in the harvesting of long wavelengths in unused portions of infrared light. We present an up to 20% improvement of the photocatalytic action of the commercial benchmark TiO2 efficient photocatalyst in the decomposition of methylene blue in water under Xe-lamp irradiation, and also an outstanding enhancement by a factor of about 2.5 of the photolytic degradation rate of this pollutant. Our results prove that the ultraviolet (UV) radiation that reaches the TiO2 particles is increased by the addition of the RE-doped powder material into a slurry-type photo-reactor, boosting both the photocatalytic and photolytic degradation rates. Thus, we show the feasibility of handling and transforming the incoming infrared radiation, bridging the UV gap of the photocatalytic semiconductor. Let us turn the infrared into the blue; there is plenty of energy at the bottom.

A Way to Weld Sheet Metal with Double-Electrode GMAW

This paper designed a double-electrode GMAW(gas metal arc welding) system. This system includes main arc and bypass arc. Main arc (Base metal current: Ibm) is supplied with Constant Current power (CC mode) and bypass arc (bypass current: Ibp) is Constant Voltage power (CV mode). Main arc electrode used common carbon wire, bypass arc electrode used water cool copper. Welding experiment shows this DE-GMAW can change common metal transfer into spray transfer with lowest critical total current (Itotal) 200 amps. When Ibm decreases and bypass voltage increases, this critical current will increase and it is less than 230 amps when keeping spray transfer. High speed video proved that metal transfer is changed from spray transfer to globular transfer.

A Simple Self-Breakdown Sharpening Switch With Low Jitter and Stable Breakdown Voltage

Normally, a three-electrode spark-gap switch is controlled by the application of an external trigger impulse. In this paper, a novel self-breakdown sharpening switch based on the three-electrode spark-gap switch is proposed. However, in this paper, the trigger electrode is connected to ground through a resistor, with the prespark between the trigger and the main electrodes providing the electrons and ions that initiate conduction of the main gap. A prototype sharpening switch with a breakdown voltage of 116.0 kV ± 1.0 kV and a breakdown time of 3.396 μs ± 0.036 μs is described. When compared with a conventional two-electrode spark-gap sharpening switch, the novel sharpening switch has both a more stable breakdown voltage and lower jitter, and the dc breakdown and impulse breakdown characteristics of the two types of switches are presented and compared. When the impedance of the resistor connected to the trigger electrode is high, it is demonstrated that both the value of this resistor and also the type of load have little effect on the characteristics of the novel switch. However, the breakdown voltage of the novel sharpening switch was found to be sensitive to the rise time of the input pulse from the trigger generator. The prototype sharpening switch has a lifetime at least 20 000 shots and is now in use in a major pulsed power conditioning system.

Current Steering with Partial Tripolar Stimulation Mode in Cochlear Implants

The large spread of excitation is a major cause of poor spectral resolution for cochlear implant (CI) users. Partial tripolar (pTP) mode has been proposed to reduce current spread by returning an equally distributed fraction (0.5 × σ) of current to two flanking electrodes and the rest to an extra-cochlear ground. This study tested the efficacy of incorporating current steering into pTP mode to add spectral channels. Different proportions of current [α × σ and (1 - α) × σ] were returned to the basal and apical flanking electrodes respectively to shape the electric field. Loudness and pitch perception with α from 0 to 1 in steps of 0.1 was simulated with a computational model of CI stimulation and tested on the apical, middle, and basal electrodes of six CI subjects. The highest σ allowing for full loudness growth within the implant compliance limit was chosen for each main electrode. Pitch ranking was measured between pairs of loudness-balanced steered pTP stimuli with an α interval of 0.1 at the most comfortable level. Results demonstrated that steered pTP stimuli with α around 0.5 required more current to achieve equal loudness than those with α around 0 or 1, maybe due to more focused excitation patterns. Subjects usually perceived decreasing pitches as α increased from 0 to 1, somewhat consistent with the apical shift of the center of gravity of excitation pattern in the model. Pitch discrimination was not better with α around 0.5 than with α around 0 or 1, except for some subjects and electrodes. For three subjects with better pitch discrimination, about half of the pitch ranges of two adjacent main electrodes overlapped with each other in steered pTP mode. These results suggest that current steering with focused pTP mode may improve spectral resolution and pitch perception with CIs.

Steady-State Voltammetry of a Microelectrode in a Closed Bipolar Cell

Here we report the theory and experimental study of the steady-state voltammetric behavior of a microelectrode used as a limiting pole in a closed bipolar electrochemical cell. We show that the steady-state voltammetric response of a microelectrode used in a closed bipolar cell can be quantitatively understood by considering the responses of both poles in their respective conventional two-electrode setups. In comparison to a conventional electrochemical cell, the voltammetric response of the bipolar cell has a similar sigmoidal shape and limiting current; however, the response is often slower than that of the typical two-electrode setup. This leads to a broader voltammogram and a decreased wave slope, which can be somewhat misleading, causing the appearance that the process being studied is irreversible when it instead can be a result of the coupling of two reversible processes. We show that a large limiting current on the excess pole would facilitate the observation of a faster voltammetric response and that both redox concentration and electrode area of the excess pole affect the wave shape. Both factors should be maximized in electroanalytical experiments in order to obtain fast voltammetric responses on the main electrode of interest and to detect quick changes in analyte concentrations.