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Nucleation and growth of hydrogen nanobubbles are key initial steps in electrochemical water splitting. These processes remain largely unexplored due to a lack of proper tools to probe the nanobubble's interfacial structure with sufficient spatial and temporal resolution. We report the use of superresolution microscopy to image transient formation and growth of single hydrogen nanobubbles at the electrode/solution interface during electrocatalytic water splitting.We found hydrogen nanobubbles can be generated even at very early stages in water electrolysis, i.e., ~500 mV before reaching its thermodynamic reduction potential. The ability to image single nanobubbles on an electrode enabled us to observe in real time the process of hydrogen spillover from ultrathin gold nanocatalysts supported on indium-tin oxide. [ABSTRACT FROM AUTHOR]

In developed area, there is not only dense electric power grid, but also dense gas pipelines. In this situation, the DC current injected into the earth through the grounding electrodes of a high-voltage DC system would aggravate the corrosion and even destroy the protection devices of the pipelines. In this study, a numerical approach is put forward to simulate the potential distribution in gas pipeline, which is regarded as long grounding system with insulating coating on the grounding conductor. The main cathodic protection methods for the pipeline are also modelled. The approach is validated by the experiment on a reduced-scale model. With this approach, the effectiveness of the measures to reduce the electrode potential distribution along the pipelines is analysed. [ABSTRACT FROM AUTHOR]

In this paper, a multiple-ring-modulated junction termination extension (MRM-JTE) technology for large-area silicon carbide PiN rectifier rated at 4500 V is proposed and experimentally investigated using a standard two-zone JTE (TZ-JTE) process without extra process steps or masks. Multiple modulation rings embedded inside JTE region, which is similar to varied lateral doping technology widely used in silicon devices, form a gradual decrease of effective charges in the termination region. MRM combines the advantages of two termination techniques, namely, ring-assisted JTE and space-modulated JTE, to enlarge the optimum JTE-dose window with high reverse blocking voltage in comparison with conventional TZ-JTE. A breakdown voltage of 4940 V at a leakage current of 1 μA is achieved from fabricated MRM-JTE rectifiers with a 36-μm-thick N- epilayer doped to 1.8 × 1015 cm-3, which is 92% of the ideal parallel-plane value. A forward current of 50 A has been measured at a forward voltage drop of 3.9 V for devices with an active anode area of 9.2 mm2, corresponding to low differential on-resistance of 1.8 mQ · cm2. The simulation and experimental results show that the proposed device exhibits approximately 2 times JTE dose tolerance window improvement with respect to the breakdown voltage of 4500 V. [ABSTRACT FROM AUTHOR]

This paper presents the experimental measurement and numerical analysis of the current-voltage characteristics of dc corona discharges in air between coaxial cylinders. The current-voltage characteristics for both positive and negative corona discharges were measured within a specially designed corona cage. Then the measured results were fitted by different empirical formulae and analyzed by the fluid model. The current-voltage characteristics between coaxial cylinders can be expressed as I = C(U - U0)m, where m is within the range 1.5-2.0, which is similar to the point-plane electrode system. The ionization region has no significant effect on the current-voltage characteristic under a low corona current, while it will affect the distribution for the negative corona under a high corona current. The surface onset fields and ion mobilities were emphatically discussed. [ABSTRACT FROM AUTHOR]

A number of Li-deficient MgO-doped LiNbO3 (LN) crystals with different Li2O contents ranging from 43.4 mol. % to 44.5 mol. % were prepared by carrying out the Li-poor vapor transport equilibration treatment on 5 mol. % (in growth melt) MgO-doped LN crystals. Unclamped electro-optic (EO) coefficients γ13 and γ33 of these crystals were measured by Mach-Zehnder interferometry. The results show that γ13 (γ33) increases linearly by ~14% (11%) as the Li2O content decreases from 44.5 mol. % of the as-grown state to 43.4 mol. % of the Li-deficient state. This feature is desired for the EO application of the Li-deficient MgO:LN crystal. [ABSTRACT FROM AUTHOR]

Porous α-Fe2O3 nanowires are synthesized by a simple wet chemical method with a precursor of peroxyacetyl nitrate (PAN), and α-Fe2O3 nanoparticles are also synthesized in the same way except for the addition of PAN. Gas sensors are fabricated by coating the samples on ceramic tubes with Au signal electrodes and Ni-Cr heaters. A sensing investigation reveals that the porous α-Fe2O3 nanowires have a higher sensitivity compared to α-Fe2O3 nanoparticles at 260°C. The corresponding sensor response (RaRg) is 18.2 at the maximum to 100 ppm acetone, and the response and recovery times are about 8 and 12 s, respectively. The porous and one-dimensional nanostructures of the porous α-Fe2O3 nanowires benefit for the gas-absorption and electrical-signal-transfer, and thus improve the sensor sensitivity consequentially. [ABSTRACT FROM AUTHOR]

Carbon-fiber-microelectrode arrays (MEAs) have been utilized to electrochenilcally image neurochemical secretion from individual pheochromocytoma (PC12) cells. Dopamine release events were elecirochemicaily monitored from seven different locations on single Pci 2 cells using alternately constant-potential amperomehy and fast-scan cyclic voltammetzy (FSCV). Cyclic voltammetry, when compared to amperometry, can provide excellent chemical resolution; however, spatial and temporal resolution are both compromised. The spatial and temporal resolution of these two methods have been quantitatively compared and the differences explained using models of molecular diffusion at the nanogap between the electrode and the cell. A nuinencal simulation of the molecular flux reveals that the diffusion of dopamine molecules and elecirochemical reactions both play important roles in the temporal resolution of elecirochemical imaging. The simulation also reveals that the diffusion and electrode potential cause the differences in signal crosstalk between electrodes when comparing amperometxy and FSCV. [ABSTRACT FROM AUTHOR]

This paper analyzes the influence of coke bed on the heat dissipation around high voltage direct current grounding electrode. By using a method coupling moment method with boundary element method, the influence of coke bed on the leakage current distribution is analyzed. Then, the affected current distribution in the soil is achieved. By using a finite difference method, the temperature distribution caused by the affected current flow is achieved. Some verification samples are also presented in this paper. [ABSTRACT FROM AUTHOR]

When dc current is injected into the earth through the grounding electrodes of an HVDC system, transformers in an ac system may be under dc bias if the dc currents flowing through the transformers are large enough. In this paper, a circuit model is presented to calculate the dc current distribution in an ac power system caused by the ground return current of a dc system. A complex image method is used to calculate the ground potential rise of each substation in multilayer earth. An indirect boundary element method is used to take into account the effects of mountains, rivers, and sea. The circuit equations are used to take into account the effects of the transmission lines. By using the method, the dc current distribution and the effectiveness of restraining measure in an ac power system are analyzed. The method and the results are not only useful for analyzing the influence of the ground return current from an HVDC ground electrode on ac power systems, but also useful for analyzing the effectiveness of the restraining measure. [ABSTRACT FROM AUTHOR]

Electrostatic-gated transport in chemically modified glass nanopore electrodes with orifice radii as small as 15 nm is reported. A single conical-shaped nanopore in glass, with a ∼1 μm radius Pt disk located at the pore base, is prepared by etching the exposed surface of a glass-sealed Pt nanodisk. The electrochemical response of the nanopore electrode corresponds to diffusion of redox-active species through the nanopore orifice to the Pt microdisk. Silanization of the exterior glass surface with Cl(Me)2Si(CH2)3CN and the interior pore surface with EtO(Me)2Si(CH2)3NH2 introduces pH-dependent ion selectivity at the pore orifice, a consequence of the electrostatic interactions between the redox ions and protonated surface amines. Nanopore electrodes with very small pore orifice radii (< ∼50 nm) display anion permselectively at pH < 4, as demonstrated by electrochemical measurement of transport through the pore orifice. Ion selective transport vanishes at pH > 6 or when the pore radius is significantly larger than the Debye screening length, consistent with the observed ion selectivity resulting from electrostatic interactions. The ability to introduce different surface functionalities to the interior and exterior surfaces of glass nanopores is demonstrated using fluorescence microscopy to monitor the localized covalent attachment of 5-(and 6)-carboxytetramethylrhodamine succinimidyl ester to interior pore surfaces previously silanized with EtO(Me)2Si(CH2)3NH2. [ABSTRACT FROM AUTHOR]

When dc current is injected into the earth through the grounding electrodes of a high-voltage direct current (HVDC) system, transformers in ac system may be under dc bias if the dc currents flowing through the transformers are large enough. In this paper, a numerical method coupling the method of moments (MoM) to circuit equations is presented to calculate the dc current distribution in ac power system caused by an HVDC system. The MoM is used to calculate the electric fields in complex earth structure caused by all the grounding systems including the dc grounding electrodes, the ac substation grounding systems and the long metal pipe lines. The circuit equations are coupled to the moment method to take account of the effects of the transmission lines. By using the method, the dc current distribution in an ac power system caused by an HVDC system is analyzed. Some useful conclusions are drawn from the analyzed results. [ABSTRACT FROM AUTHOR]

The steady-state voltammetric behavior of truncated conical nanopore electrodes (20−200 nm orifice radii) has been investigated in low ionic strength solutions. Voltammetric currents at the nanopore electrode reflect both diffusive and migrational fluxes of the redox molecule and, thus, are strongly dependent on the charge of the redox molecule and the relative concentrations of the supporting electrolyte and redox molecule. In acetonitrile solutions, the limiting current for the oxidation of the positively charged ferrocenylmethyltrimethylammonium ion is suppressed at low supporting electrolyte concentrations, while the limiting current for the oxidation of the neutral species ferrocene is unaffected by the ionic strength. The dependence of the limiting current on the relative concentrations of the supporting electrolyte and redox molecule is accurately predicted by theory previously developed for microdisk electrodes. Anomalous values of the voltammetric half-wave potential observed at very small nanopore electrodes (<50 nm radius orifice radii) are ascribed to a boundary potential between the pore interior and bulk solution (i.e., a Donnan-type potential). [ABSTRACT FROM AUTHOR]

The steady-state voltammetric response of the truncated conical-shaped glass nanopore electrode is presented. Analytical theory, finite-element simulations, and experimental measurement of the diffusive flux of a redox molecule through the pore orifice demonstrate that the steady-state current decreases rapidly as the pore depth increases and then asymptotically approaches a constant value when the pore depth is ∼50× larger than the pore orifice. The asymptotic limit of the steady-sate current is only a function of the pore orifice radius and the cone angle of the pore and has a finite value for all cone angles greater than zero. Experimental confirmation of the predicted dependence on pore depth is obtained using nanopore electrodes with 100-1000 nm orifice radii, by measuring the steady-state voltammetric current corresponding to the oxidation of ferrocene in acetonitrile solutions containing an excess of supporting electrolyte. [ABSTRACT FROM AUTHOR]

In a high soil resistivity area, counterpoise wires are applied to decrease the grounding resistance of tower grounding devices. If the conductor of counterpoise wire is very long, although the power frequency grounding resistance of the tower grounding device ii decreased, the lightning protection performance of the transmission line is still not good. The influences of the length of grounding electrodes on the lightning transient characteristic were analyzed. The dynamic and nonlinear effect of soil ionization around the grounding electrode was considered in the analysis model of transient characteristics for the grounding electrodes under lightning impulse. The counterpoise wire has an effective length when lightning passes through it. When the length of a grounding electrode exceeds the effective length, the grounding conductor will not be utilized effectively. The simulating experiments were performed to analyze influences of the length of the counterpoise wire on the impulse characteristics. The formulae to calculate the impulse effective lengths of counterpoise wires were proposed. The model proposed in the paper has been validated by comparing the numerical results with experimental tests. [ABSTRACT FROM AUTHOR]

A Single-Power Alternating Current (SPAC) instrument was used to measure the low-impedance acupoints around Ho-Ku (LI-4), Yang-Hsi (LI-5), Yang-Ch'ih (TB-4), Yang-Ku (SI-5), T'ai-Yuan (Lu-9), Ta-Lung (EH-7) and Shen-Men (He-7). A four-electrode instrument was used to measure the subcutaneous impedance at these low-impedance acupoints and adjacent control points on 12 healthy people. The mean subcutaneous impedance at the acupoints was 49.8±8.4 Ω, significantly lower than the impedance of 53.5±9.3 Ω for the control points (P<0.005). Of the seven acupoints, five (71%) had significantly lower impedances than the mean impedance for the adjacent control points. Seven of the 14 control points had significantly higher impedances than the adjacent acupoints, with most control points (93%) having higher impedances than adjacent acupoints. In conclusion, subcutaneous impedance is lower at the low-impedance points as measured with the SPAC two-electrode method. One interpretation of these results is that more interstitial fluid lies beneath the low-impedance acupoints. [ABSTRACT FROM AUTHOR]

A new lateral power MOSFET structure [folded-accumulation LDMOS (FALDMOS)] is proposed, in which the silicon-substrate surface is trenched to form a folded shape from the channel to the drain electrode and the gate is extended to the drain. The majority-carrier accumulation layer is formed as the device is in ON state due to the extended gate in the drift region whose concentration is higher than that in a conventional LDMOS at the same breakdown voltage (By), resulting from the additional electric-field modulation, and an extra majority carrier is introduced on the sidewall of the trench, which reduced the on-resistance of the drift region further. In addition, the channel density is doubled because of trenching the folded channel, which reduced the channel on-resistance. It indicates by simulation that the specific on-resistance of 4.6Ω · mm2 with a BV of 27.4 V in FALDMOS is lower than that of the previously reported lowest one. [ABSTRACT FROM AUTHOR]

Plasma synthetic jet actuator (PSJA) has shown wide and promising application prospects in a high speed flow control field, due to its rapid response, high exhaust velocity, and non-moving components. In this paper, the total pressure profile of a plasma synthetic jet (PSJ) is measured and a new method is developed to evaluate the pulsed thrust of the PSJA. The influence of geometrical parameters including the electrode distance, the orifice diameter, and the throat length on PSJA performance is analyzed based on the pulsed thrust, the discharge characteristics, and the schlieren images. When varying the electrode distance, the dominant factor determining the jet intensity is the heating volume instead of the discharge energy. For the arc discharge, the electrode distance should be extended to increase both the jet velocity and the jet duration time. The design of the orifice diameter should be based on the controlled flow field. A large orifice diameter produces a strong perturbation with short time duration, while a small orifice diameter induces a lasting jet with low mass flux. In order to obtain better high frequency performance, the throat length should be shortened on the condition that the structural strength of the PSJA is maintained, while there is almost no influence of the throat length on the single cycle performance of the PSJA. Once the discharge energy is fixed, the pulsed thrust remains almost unchanged with different orifice diameters and throat lengths. These three geometrical parameters are independent to some extent and can be optimized separately. [ABSTRACT FROM AUTHOR]

Here we report the use of fast-scan cyclic voltammetry (FSCV) to study transient collision and immobilization events of single electro catalytic metal nanoparticles (NPs) on an inert electrode. In this study, a fast, repetitive voltage signal is continuously scanned on an ultramicroelectrode and its faradaic signal is recorded. Electrocatalytically active metal NPs are allowed to collide and immobilize on the electrode resulting in the direct recording of the transient voltammetric response of single NPs. This approach enables one to obtain the transient voltammetric response and electrocatalytic effects of single catalytic NPs as they interact with an inert electrode. The use of FSCV has enabled us to obtain chemical information, which is otherwise difficult to study with previous amperometric methods. [ABSTRACT FROM AUTHOR]

In this technical note, we report a process in scaling down the fabrication of Au disk nanoelectrodes as small as 4 nm in radii. We have developed a bottom-up approach toward the fabrication of individual disk-shape Au nanoelectrodes. This new approach is based upon electrochemical deposition of Au in a silica nanopore electrode and involves the following four steps. First, a laser-assisted pulling process is employed to fabricate a disk-shape Pt nanoelectrode. Second, a Pt nanopore electrode is obtained by electrochemically etching the Pt from the disk nanoelectrode. Third, a Au metal nanowire is electrochemically deposited using the Pt nanopore electrode as a template. In the last step, the Au electrode is slightly polished to expose a disk-shape Au nanoelectrode, whose size is determined by the size of the initial Pt nanoelectrode. Steady-state voltammetry in the presence of ferrocene has been used to characterize these Au nanoelectrodes. The Au nanoelectrodes are also characterized using cyclic voltammetry in a H2SO4 solution. The results show characteristic peaks corresponding to the formation of Au surface oxides and their subsequent reduction. The Au nanoelectrodes are modified with 6-(ferrocenyl)hexanethiol molecules, and cyclic voltammetry is used to characterize the ferrocene molecules attached at the Au. As an application, we have constructed Au single-nanoparticle electrodes (SNPEs) using the Au disk nanoelectrodes fabricated by electrochemical deposition. Our initial results of such SNPEs show excellent electrochemical response from single Au nanoparticles. [ABSTRACT FROM AUTHOR]

Steady-state electrochemical responses have been obtained at single Au nanoparticles using Pt nanoelectrodes. A Au single-nanoparticle electrode (SNPE) is constructed by chemically immobilizing a single Au nanoparticle at a SiO2-encapsulated Pt disk nanoelectrode, which was previously modified by an amine-terminated silane. The Au SNPE has been characterized by transmission electron microscopy, underpotential deposition of Cu, and steady-state cyclic voltammetry. It has been found that the presence of a single Au nanoparticle enhances the electron transfer from the Pt nanoelectrode to the redox molecules, and the voltammetric response at the Au SNPE depends on the size of the Au nanoparticle. The Au SNPE has been utilized to examine the oxygen-reduction reaction in a KOH solution to explore the feasibility of measuring the electrocatalytic activity at a single-nanoparticle level. It has been shown that the electrocatalytic activity of single Au nanoparticles can be directly measured using SNPEs, and the electrocatalytic activity is dependent on the size of the Au nanoparticles. This study can help to understand the structure-function relationship in nanoparticle-based electrocatalysis. [ABSTRACT FROM AUTHOR]

The preparation and characterization of Pt nanoelecirodes in the range of 1 to 3 nm in radii are reported. A Pt microwire is sealed into a bilayer quartz capillary and pulled into an ultrasharp Pt nanowire sealed in a silica tip using a laser-assisted puffing process. The ultrasharp tip is then sealed into a piece of glass tubing, which is manually polished to expose the Pt. Transmission electron microscopy and steady-state voltammetry are utilized to characterize the nanoelectoxles. The results show that the minimum size of the Pt nanoelectrode is determined by the size of the Pt microwire and parameters used in the putting process. The heterogeneous electron transfer rate constant for the oxidation of ferrocene, ferrocenemethanol, and potassium hexachioroiridate (III) are determined from steady-state voltanunetmy using the method of Mirkin and Bard and are found to be k° = 7.6 ± 3.4 cm/s and a = 0.85 ± 0.06 for ferrocene, k° = 7.4 ± 6.9 cm/s and a = 0.78 ± 0.16 for ferrocenemethanol, and k° = 6.0 ± 4.2 cm/s and a 0.72 ± 0.15 for IrCl63-. [ABSTRACT FROM AUTHOR]

A promising candidate for a top cell in a tandem solar cell setup is a superstate, high bandgap, CIGS (Copper Indium Gallium Diselenide) solar cell. To realize a tandem cell, both, front and back contact of the top cell must be transparent. In this work a molybdenum metal mesh electrode with four pattern derivatives is presented, which are designed towards this implementation in a tandem cell setup. The electrode consists of two-micron wide fingers arranged in an industry typical H-grid pattern and in a hexagonal shaped pattern, with each of these patterns being comprised of a derivative with and without tapered busbars. The electrode's micro structure, crystal orientation, surface roughness, electrical properties and optical properties are investigated. The manufacturing process as well as a comparison of this works electrodes with various competing electrode types is also presented. All electrode derivatives show excellent transmittance of up to 97% within and beyond the visible spectrum while retaining acceptable sheet resistances of about 30 Ω/□. [ABSTRACT FROM AUTHOR]

Here we report the direct observation and quantitative analysis of single redox events on a modified indium-tin oxide (ITO) electrode. The key in the observation of single redox events are the use of a fluorogenic redox species and the nanoconfinement and hindered redox diffusion inside 3-nm-diameter silica nanochannels. A simple electrochemical process was used to grow an ultrathin silica film (~100 nm) consisting of highly ordered parallel nanochannels exposing the electrode surface from the bottom. The electrode-supported 3-nm-diameter nanochannels temporally trap fluorescent resorufin molecules resulting in hindered molecular diffusion in the vicinity of the electrode surface. Adsorption, desorption, and heterogeneous redox events of individual resorufin molecules can be studied using total-internal reflection fluorescence (TIRF). The rate constants of adsorption and desorption processes of resorufin were characterized from single-molecule analysis to be (1.73 ± 0.08) x 10- cm⋅s-1 and 15.71 ± 0.76 s-1, respectively. The redox events of resorufin to the non-fluorescent dihydroresorufin were investigated by analyzing the change in surface population of single resorufin molecules with applied potential. The scan-rate-dependent molecular counting results (single-molecule fluorescence voltammetry) indicated a surface-controlled electrochemical kinetics of the resorufin reduction on the modified ITO electrode. This study demonstrates the great potential of mesoporous silica as a useful modification scheme for studying single redox events on a variety of transparent substrates such as ITO electrodes and gold or carbon film coated glass electrodes. The ability to electrochemically grow and transfer mesoporous silica films onto other substrates makes them an attractive material for future studies in spatial heterogeneity of electrocatalytic surfaces. [ABSTRACT FROM AUTHOR]