Vertical Electrodes Research Articles

Flow field characterization between vertical plate electrodes in a bench-scale cell of electrochemical water softening

Abstract To analyze the effect of flow characteristics on electrochemical water softening, characteristics of flow fields in the vicinity of vertical plate electrodes in a bench-scale electrolysis cell for electrochemical water softening were visualized using particle image velocimetry technology, and the hardness drop values under different process conditions were measured. Properly increasing the current density or reducing the electrode spacing can increase the average flow velocity in the electrode gap. Excessive current density will cause bubble accumulation, form a bubble vortex, interfere with the orderly flow of surrounding liquid and reduce mass transfer efficiency. When the electrode spacing is 120 mm, the highest water softening efficiency measured at the current density of 60 A/m2 is 16.56%. When the current density is 50 A/m2, the highest average speed measured at the electrode spacing of 60 mm is 0.00169 m/s, but the highest water softening efficiency measured at the electrode spacing of 90 mm is 23.3%.The circulation efficiency in the electrode gap of a semi-closed structure is lower than that of a free convection structure. The behavior of bubbles is the key to flow and mass transfer. It is important to consider its influence on bubble behavior when optimizing electrochemical parameters.

Development of a Novel Reverse Offset Printer Equipped with Double-Layer Blanket (DLB) for Micropattern Printing on 3D Curved Surfaces

The double-layer blanket (DLB) reverse offset is a newly designed printing process for patterning electronic circuits on a 3D curved surface. Unlike the existing reverse offset process, the DLB reverse offset utilizes an offset roll composed of two layers comprising polydimethylsiloxane (PDMS) and a thick, soft cushioned rubber to print microelectrode patterns and transparent electrodes on a curved surface. The optimal printing process was determined by adjusting the printing pressure and printing speed for horizontal and vertical micropatterns, based on which transparent electrodes with metal mesh and honeycomb structures with a line width of 30 μm and pitch of 600 μm with micropatterns ranging from 30 μm to 60 μm were printed on a curved surface. Ag ink was used, and the 3D curved surface indicated a print quality similar to that of the flat surface for both the vertical and horizontal patterns and transparent electrodes. The DLB reverse offset technique demonstrated the possibility of printing on a 3D curved surface and is expected to broaden the range of printed electronics to applications such as smart glasses and 3D shape sensors.

Construction of three-dimensional (3D) vertical nanosheets electrode with electrochemical capacity applied to microsupercapattery

The preparation of heterostructure composites is regarded as an effective measure to enhance the electrochemical performances of pure component materials for energy conversion and storage. This paper reports a rapid microwave process to synthesize novel hierarchical multi-walled carbon nano-tubes and graphene nano-ribbons/Co–Ni LDH (MWGR/Co–Ni LDH) composites with superior performances in supercapattery. MWCNTs-GONRs with high conductivity, structural stability and electrochemical properties, and LDH with the construction of p-n junction are also profitable to transpire redox reaction. Thus, MWGR/Co–Ni LDH exhibites the distinctive heterostructure and splendid electrochemical properties (a high specific capacitance of 1030.2 C g−1 at 1 A g−1). In addition, the as-prepared MWGR/Co–Ni LDH//AC device performs the maximum energy density of 47.2 Wh kg−1 at power density of 0.85 kW kg−1 and good cycling performance of 88.8% retention after 10,000 cycles at 10 A g−1. Furthermore, the assembled asymmetric supercapattery (ACS) is adequate to provide energy for multiple lights emitting diodes (LEDs), which holds great promising practical applications for supercapattery.

Nitrogen, Oxygen-Codoped Vertical Graphene Arrays Coated 3D Flexible Carbon Nanofibers with High Silicon Content as an Ultrastable Anode for Superior Lithium Storage.

Free‐standing and foldable electrodes with high energy density and long lifespan have recently elicited attention on the development of lithium‐ion batteries (LIBs) for flexible electronic devices. However, both low energy density and slow kinetics in cycling impede their practical applications. In this work, a free‐standing and binder‐free N, O‐codoped 3D vertical graphene carbon nanofibers electrode with ultra‐high silicon content (VGAs@Si@CNFs) is developed via electrospinning, subsequent thermal treatment, and chemical vapor deposition processes. The as‐prepared VGAs@Si@CNFs electrode exhibits excellent conductivity and flexibility because of the high graphitized carbon nanofiber network and abundant vertical graphene arrays. Such 3D all‐carbon architecture can be fabulous for providing a conductive and mechanically robust network, further improving the kinetics and restraining the volume expansion of Si NPs, especially with an ultra‐high Si content (>90 wt%). As a result, the VGAs@Si@CNFs composite demonstrates a superior specific capacity (3619.5 mAh g−1 at 0.05 A g−1), ultralong lifespan, and outstanding rate capability (1093.1 mAh g−1 after 1500 cycles at 8 A g−1) as a free‐standing anode for LIBs. It is believed that this work offers an exciting method for developing free‐standing and high‐energy‐density electrodes for other energy storage devices.

Performance of Grounding Electrodes Under Lightning Strokes in Uniform and Two-Layer Soils Considering Soil Ionization

This article presented the characteristics of the grounding electrodes in uniform and two layer soils when subjected to lightning including the impacts of soil ionization with frequency, soil resistivity, and permittivity variations. The critical breakdown field strength of two layer soils with different values of the reflection factors was presented. The transient probabilistic grounding potential rise and the transient impedances of the horizontal and vertical electrodes were investigated in uniform and two layer soils including the effect of soil ionization with frequency. Finally, the influences of resistivity and permittivity variations which have substantial impacts on the electric field at the occurrence of the soil ionization were considered. Moreover, transmission line approach (TL) with the aid of ATP has been used to compute the transient grounding voltages. The results indicated that the reflection factor has a significant impact on the equivalent radius of the grounding electrode. It is also observed that the peak values of the lightning induced voltages decreases sharply when the soil ionization phenomenon considering the variations in soil resistivity and permittivity with the stroke frequency changes. Furthermore, the impedances of the burial electrodes that have negative reflection factors were lower than that in case of positive reflection factors.

A Method for Grounding Resistance Calculation of the Vertical Grounding Electrode

A Method for Grounding Resistance Calculation of the Vertical Grounding Electrode

Ultrafast photoresponse of vertically oriented TMD films probed in a vertical electrode configuration on Si chips.

Integrated photodetectors based on transition metal dichalcogenides (TMDs) face the challenge of growing their high-quality crystals directly on chips or transferring them to the desired locations of components by applying multi-step processes. Herein, we show that vertically oriented polycrystalline thin films of MoS2 and WS2 grown by sulfurization of Mo and W sputtered on highly doped Si are robust solutions to achieve on-chip photodetectors with a sensitivity of up to 1 mA W−1 and an ultrafast response time in the sub-μs regime by simply probing the device in a vertical arrangement, i.e., parallel to the basal planes of TMDs. These results are two orders of magnitude better than those measured earlier in lateral probing setups having both electrodes on top of vertically aligned polycrystalline TMD films. Accordingly, our study suggests that easy-to-grow vertically oriented polycrystalline thin film structures may be viable components in fast photodetectors as well as in imaging, sensing and telecommunication devices.

Boron and nitrogen co-doped vertical graphene electrodes for scalp electroencephalogram recording

Graphene has shown immense potential for applications in monitoring scalp electroencephalogram (EEG) signals. However, the radial head shape, high-resistance scalp cuticle, and hair prevent graphene from contacting skin, resulting in high contact impedances and low signal-to-noise ratios (SNRs) in EEG signals. Therefore, B and N co-doped vertical graphene (BNVG) electrodes are synthesized to improve the skin affinity and sweat adsorption capacity. X-ray photoelectron spectroscopy results show that the series of BNVG electrodes comprise B-doping contents of 1.25–9.85 at% and N-doping contents of 1.12–6.48 at%. A systematic analysis of the effects of B and N atom contents on the real-time scalp-contact resistances, EEG correlation coefficients between BNVG and Ag/AgCl electrodes, and SNRs of the EEG signals are conducted. The BNVG electrode comprising 4.47 at% B and 3.18 at% N is determined as the optimum electrode for scalp EEG signal acquisition. Furthermore, an EEG cap assembled with 19 optimized BNVG electrodes records spontaneous and evoked EEG signals. The BNVG-based EEG cap used with sweat or aqueous NaCl solution is confirmed to be advantageous and can be applied to clinical and brain-computer interface systems.

3D Vertical Arrays of Nanomaterials for Microscaled Energy Storage Devices

ConspectusThe ever-growing market of miniature and autonomous electronics has motivated an upsurge of interest in exploiting microscaled energy storage devices (MESDs) such as microbatteries and microsupercapacitors. To meet the burgeoning demand for energy, electrodes with high mass loading to synchronously raise areal energy and power are extensively pursued. Increasing the thickness of the conventional thin-film electrode to augment the areal loading is not a feasible approach, as it leads to elongated solid diffusion path, thereby limiting the power output of microdevices. This scenario is more unfavorable for solid-state microdevices because ion diffusion in solid electrolytes is more sluggish than in liquid electrolytes. To tackle such a dilemma, adoption of 3D array electrodes has been proposed to pave a new path for the design and development of MESDs.In comparison with 2D electrode geometries, the state-of-the-art designs of 3D vertical arrays have proved very effective in mitigating the manufacture and performance challenges related to MESDs. First of all, thick electrodes with high loading can be engineered while the nanoscale diffusion of ions is maintained, thus significantly enhancing areal energy without compromising the power output. Second, electrodes based on arrays grown on conductive substrates waive the addition of binders and conducting agents, thereby remarkably simplifying the fabrication procedures and reducing the processing cost. Third, the presence of organized channels in the electrode arrays not only accelerates ion diffusion, but also offers enough space to accommodate the electrode swelling upon energy storage. Fourth, 3D arrays possess large surface areas and massive reactive sties, enabling relatively homogeneous current distribution throughout the electrode surface.In the past few years, we have developed several techniques to design and produce 3D vertical electrode arrays for robust microenergy storage. Through 3D electrode design, substantial improvement in the energy and power within a given footprint area has been achieved. In this Account, we highlight such improvements and progresses in our groups as well as some critical advancements acquired in other teams. As research in this area is still at an early stage, the majority of the important progresses is embodied in the form of materials design and electrode fabrication. The remaining challenges and possible solutions are discussed, and insights for further research are also proposed.

Numerical investigation of electro-thermo-convection and heat transfer enhancement in a square enclosure with various electrode arrangements

The dielectric fluid was normally used to electrically shield high-voltage applications. However, recent studies on the electrohydrodynamic technique using the dielectric fluid were attentively conducted to obtain heat transfer enhancement in keeping with its electrical-insulating feature. This study numerically investigates the electro-thermo-convection in a two-dimensional square enclosure with hot and cold vertical walls. The heat transfer rate in the free convection inside the enclosure can be significantly improved by the injection of space charges and working of the Coulomb force. In this study, we tested several electrode arrangements, including alternately arranged electrode pairs on walls, under the intense charge injection condition. Consequently, the vertical arrangements of the electrode pairs demonstrate a higher heat transfer rate than the horizontal arrangements. The heat transfer coefficient of the vertical electrode pairs at a Rayleigh number of 5000 and an electric Rayleigh number of 200 is larger than three times that of the horizontal electrode pairs. Using fluid with a Prandtl number of 10, the results of the stream lines, isotherms, and space charge distributions are summarized herein for various thermal and electrical buoyant conditions.

Fabrication of a Hydrogenated Amorphous Silicon Detector in 3-D Geometry and Preliminary Test on Planar Prototypes

Hydrogenated amorphous silicon (a-Si:H) can be produced by plasma-enhanced chemical vapor deposition (PECVD) of SiH4 (silane) mixed with hydrogen. The resulting material shows outstanding radiation hardness properties and can be deposited on a wide variety of substrates. Devices employing a-Si:H technologies have been used to detect many different kinds of radiation, namely, minimum ionizing particles (MIPs), X-rays, neutrons, and ions, as well as low-energy protons and alphas. However, the detection of MIPs using planar a-Si:H diodes has proven difficult due to their unsatisfactory S/N ratio arising from a combination of high leakage current, high capacitance, and limited charge collection efficiency (50% at best for a 30 µm planar diode). To overcome these limitations, the 3D-SiAm collaboration proposes employing a 3D detector geometry. The use of vertical electrodes allows for a small collection distance to be maintained while preserving a large detector thickness for charge generation. The depletion voltage in this configuration can be kept below 400 V with a consequent reduction in the leakage current. In this paper, following a detailed description of the fabrication process, the results of the tests performed on the planar p-i-n structures made with ion implantation of the dopants and with carrier selective contacts are illustrated.

General Formulas for Lightning Impulse Impedance of Horizontal and Vertical Grounding Electrodes

Voltage drop developed between the grounding electrode under lightning current and distant neutral ground determines the protection efficiency. The peak value of such voltage can be computed from known impulse impedance and current peak value. For the first time, in this letter, general formulas are derived for impulse impedance of horizontal and vertical electrodes valid for any length up to 100 m, soil's resistivity of 30 to 1000 Ωm, and current impulse front time of 0.2 to 10 μs. Waveforms of typical lightning impulses given in IEC standards are used, but it is shown that results are also relevant for other impulse waveforms. Soil ionization effects are taken into account, and the accuracy of the formulas is investigated. New formulas enable an estimate of lightning protection grounding's surge efficiency in a wide range of practical situations.

Fabrication of a Conductive Poly(3,4-ethylenedioxythiophene)-Coated Polyester Nonwoven Fabric and Its Application in Flexible Piezoresistive Pressure Sensors

Poly(3,4-ethylenedioxythiophene)-coated nonwoven fabric (PEDOT@NWF) composites were prepared using ordinary polyester needle-punched nonwoven fabrics as substrates via in situ vapor phase polymerization (VPP) technique. The prepared PEDOT@NWF conductive composite has a uniform PEDOT coating on the surface of the fibers. Factors which may affect the polymerization effect, such as oxidant concentration, reaction time, and other parameters were explored, and a series of morphological, structural, and electrical properties of the prepared conductive nonwoven fabrics were analyzed. Furthermore, for comparison, piezoresistive pressure sensors with two different assembly methods (vertical electrode and horizontal electrode) were made utilizing the PEDOT@NWF material. The pressure sensing performance has also been evaluated and the as-prepared sensors exhibit good sensitivity and fast response time.

DEVELOPMENT AND MODELLING OF HIGH SPREAD CONDUCTIVITY EARTH ELECTRODES FOR COMPLEX EARTHING ARRANGEMENTS

The analysis of methods for calculating the electrical characteristics of earth electrodes in case of emergency currents of industrial frequency flowing through the elements of earthing arrangements is carried out. A method for improving complex earthing arrangements of electrical installations by optimization of their design parameters is proposed. The proposed method consists in installing an artificial earth electrode with an increased contact area of its surface with the ground, which makes it possible to increase the conductivity of earthing spreading. The use of these electrodes on the territory of projected or operating electrical installations ensures that the values of the normalized parameters of earthing arrangements are brought to permissible values. The use of the method given in the calculations of earthing arrangements requires the replacement of volumetric earth electrodes with a set of linear vertical electrodes. The design model is substantiated by equivalent electrical characteristics relative to the two-layer model of the electrical structure of the earth. The equivalent model was obtained by a given approximation of the electrical characteristics of a set of straight electrodes in the process of increasing their number to the equivalent characteristics of the reference model. In turn, the determination of the characteristics of the reference model was carried out directly by solving the boundary value problem for the potential satisfying Laplace equation using finite difference method. Theoretical investigations using induced potential method and methods of calculation of branched electric circuits with distributed parameters for calculation of electric field and resistance of the complex non-equipotential earth electrode in the ground with two-layer structure have been carried out. The developed electrodes of increased spread conductivity are mounted as experimental samples and are involved in the formation of the electrical characteristics of the earthing arrangements.

Method for determining the state of an grounding device

The article provides a method for determining the state of the grounding devices without having to open the vertical and horizontal electrodes thereof. The developed method requires the determination of the average annual significance of indirect factors, essentially influencing the corrosion state of the ground elements, such as ground humidity and the meaning wandering current.

Aluminium Recycling in Single- and Multiple-Capillary Laboratory Electrolysis Cells

This work is a contribution to the approach for Al purification and extraction from scrap using the thin-layer multiple-capillary molten salt electrochemical system. The single- and multiple-capillary cells were designed and used to study the kinetics of aluminium reduction in LiF–AlF3 and equimolar NaCl–KCl with 10 wt.% AlF3 addition at 720–850 °C. The cathodic process on the vertical liquid aluminium electrode in NaCl–KCl (+10 wt.% AlF3) in the 2.5 mm length capillary had mixed kinetics with signs of both diffusion and chemical reaction control. The apparent mass transport coefficient changed from 5.6∙10−3 cm.s−1 to 13.1∙10−3 cm.s−1 in the mentioned temperature range. The dependence between the mass transport coefficient and temperature follows an Arrhenius-type behaviour with an activation energy equal to 60.5 kJ.mol−1. In the multiple-capillary laboratory electrolysis cell, galvanostatic electrolysis in a 64LiF–36AlF3 melt showed that the electrochemical refinery can be performed at a current density of 1 A.cm−2 or higher with a total voltage drop of around 2.0 V and specific energy consumption of about 6–7 kWh.kg−1. The resistance fluctuated between 0.9 and 1.4 Ω during the electrolysis depending on the current density. Thin-layer aluminium recycling and refinery seems to be a promising approach capable of producing high-purity aluminium with low specific energy consumption.

Effect of Earthing Enhancing Compound (EEC) on Improving Tower Footing Resistance of a 500 kV Tower in a Rocky Area

This paper presents a comparative analysis of different earthing designs’ performances, with particular interest on the use of earthing enhancing compound (EEC) for a selected earthing design of 500 kV transmission towers in a rocky soil, using the SESCAD tool of the Current distribution, electromagnetic field grounding and soil structure analysis (CDEGS) software. The simulation included the interpretation of soil profile and comparison between designs A, B and C, which are currently used for the 500 kV tower footing resistance (TFR) improvement. Results showed each design had reduced the TFR by 66%, 54.7% and 63.2% for the towers T42, T48 and T50, respectively. In some cases, further improvement of TFR is required, especially in the rocky area where the soil resistivity (SR) value is of more than 500 Ω⋅m. In this case, EEC was used in Design C, encasing both the vertical and horizontal electrodes, and it reduced the TFR further by 16% to 20%. The characteristics of the soil and earthing arrangement design play an important role in achieving a low TFR value, which is directly proportional to the backflashover occurrence and thus to the transmission line performance.

Experimental investigation of a modified free-fall tribo-electrostatic separator with rotating electrodes

The impacts of the plastic particles on the vertical electrodes of the free-fall tribo-electrostatic separator (FFTES) is one of the main drawbacks of this separator for sorting millimeter-size particles. The impact on the electrode causes in general a strong reflection of the particles causing the decrease of the separation purity because the particles impacting with the electrode are ejected further toward the compartment of the other material. This paper is aimed to investigate a modified FFTES configuration with rotating cylindrical electrodes instead of flat vertical electrodes to overcome the particle impacting effect. An experimental and a numerical analysis were carried out in which the main significant factors were investigated. The experiments carried out using binary mixtures of mm-size particles showed that the rotating electrodes attenuates considerably the reflection velocity in the horizontal plane causing a significant increase of the separator performance in terms of purity and recovery rates.

Computation of ground potential rise and grounding impedance of simple arrangement of electrodes buried in frequency-dependent stratified soil

Grounding electrodes are used to provide a low-impedance dissipation path for the excess lightning or fault currents. Several studies have been dedicated to the computation of the grounding impedance of different electrode arrangements considering either the frequency dependence of soil parameters (resistivity ρ and relative permittivity εr) or the multi-layer nature of soil. This paper aims at the calculation of the grounding impedance and the ground potential rise (GPR) of simple electrode arrangements (vertical and cross electrodes) due to the injection of first and subsequent lightning currents in various configurations of soil, considering a frequency-dependent stratified soil.A frequency-domain full-wave electromagnetic solver based on the Method of Moment (MoM) that employs a stratified medium Green’s function is used to compute the grounding impedance in a frequency range of 100Hz to 10MHz. The transient GPRs are computed using the equivalent circuit of the grounding system, obtained through the application of the Vector Fitting (VF) technique and recursive convolution method.The simulation results show that considering the frequency dependence of the soil parameters has no effect on the low-frequency grounding impedance up to ≈10kHz. However, the frequency dependence of soil parameters leads to a considerable variation of the grounding impedance at higher frequencies especially for soils of higher resistivity. Furthermore, it is shown that considering the layers of soil has a more significant impact on the GPR of the vertical electrode than that of the cross electrode.

Vertical Nanowire Electrode Array for Enhanced Neurogenesis of Human Neural Stem Cells via Intracellular Electrical Stimulation.

Extracellular electrical stimulation (ES) can provide electrical potential from outside the cell membrane, but it is often ineffective due to interference from external factors such as culture medium resistance and membrane capacitance. To address this, we developed a vertical nanowire electrode array (VNEA) to directly provide intracellular electrical potential and current to cells through nanoelectrodes. Using this approach, the cell membrane resistivity and capacitance could be excluded, allowing effective ES. Human fetal neural stem cells (hfNSCs) were cultured on the VNEA for intracellular ES. Combining the structural properties of VNEA and VNEA-mediated ES, transient nanoscale perforation of the electrode was induced, promoting cell penetration and delivering current to the cell. Intracellular ES using VNEA improved the neuronal differentiation of hfNSCs more effectively than extracellular ES and facilitated electrophysiological functional maturation of hfNSCs because of the enhanced voltage-dependent ion-channel activity. The results demonstrate that VNEA with advanced nanoelectrodes serves as a highly effective culture and stimulation platform for stem-cell neurogenesis.