Influence of Current Density on the Photocatalytic Activity of Nd:TiO_(2) Coatings

The Nd:TiO_(2 )PEO coatings were formed in a phosphate-based electrolyte with the addition of Nd_(2)O_(3 )under the current density of 150,200,250 and 300 m A/cm^(2).SEM results showed that the micropores decreased on quantity and increased on scale with the increasing current density.AFM results revealed that the roughness of the coatings increased with the increasing current density.Phase and composition analysis showed that the Nd:TiO_(2) coatings were mainly composed of anatase and rutile phase.And the anatase phase content has reached the maximum value at the current density of 250 m A/cm^(2).XPS results indicated that Ti2p spin-orbit components of the Nd:TiO_(2) coatings are shifted towards higher binding energy,compared with the pure TiO_(2) coating,suggesting that some of the Nd^(3+)ions are combined with TiO_(2) lattice and led to dislocation.Photocatalytic test showed that the photocatalytic activity of Nd:TiO_(2) coatings varied in the same pattern with the anatase content variation in Nd:TiO_(2) coatings.The photocatalytic experiment results show that the photocatalytic activity of Nd:TiO_(2) coatings can be greatly enhanced with moderate amount of Nd^(3+).However,excessive amount of Nd^(3+)does not have an effective impact on the photoctalytic activity improvement.

Recent advances in design of hydrogen evolution reaction electrocatalysts at high current density:A review

The electrolysis of water powered by renewable energy sources offers a promising method of"green hydrogen"production,which is considered to be at the heart of future carbon-neutral energy systems.In the past decades,researchers have reported a number of hydrogen evolution reaction(HER)electrocatalysts with activity comparable to that of commercial Pt/C,but most of them are tested within a small current density range,typically no more than 500 mA cm^(-2).To realize the industrial application of hydrogen production from water electrolysis,it is essential to develop high-efficiency HER electrocatalysts at high current density(HCD≥500 mA cm^(-2)).Nevertheless,it remains challenging and significant to rational design HCD electrocatalysts for HER.In this paper,the design strategy of HCD electrocatalysts is discussed,and some HCD electrocatalysts for HER are reviewed in seven categories(alloy,metal oxide,metal hydroxide,metal sulfide/selenide,metal nitride,metal phosphide and other derived electrocatalysts).At the end of this article,we also pro-pose some viewpoints and prospects for the future development and research directions of HCD electrocatalysts for HER.

Deep learning approaches to recover the plasma current density profile from the safety factor based on Grad–Shafranov solutions across multiple tokamaks

Many magnetohydrodynamic stability analyses require generation of a set of equilibria with a fixed safety factor q-profile while varying other plasma parameters.A neural network(NN)-based approach is investigated that facilitates such a process.Both multilayer perceptron(MLP)-based NN and convolutional neural network(CNN)models are trained to map the q-profile to the plasma current density J-profile,and vice versa,while satisfying the Grad–Shafranov radial force balance constraint.When the initial target models are trained,using a database of semianalytically constructed numerical equilibria,an initial CNN with one convolutional layer is found to perform better than an initial MLP model.In particular,a trained initial CNN model can also predict the q-or J-profile for experimental tokamak equilibria.The performance of both initial target models is further improved by fine-tuning the training database,i.e.by adding realistic experimental equilibria with Gaussian noise.The fine-tuned target models,referred to as fine-tuned MLP and fine-tuned CNN,well reproduce the target q-or J-profile across multiple tokamak devices.As an important application,these NN-based equilibrium profile convertors can be utilized to provide a good initial guess for iterative equilibrium solvers,where the desired input quantity is the safety factor instead of the plasma current density.

Responses of the field-aligned currents in the plasma sheet boundary layer to a geomagnetic storm

Geomagnetic storms can result in large magnetic field disturbances and intense currents in the magnetosphere and even on the ground.As an important medium of momentum and energy transport among the solar wind,magnetosphere,and ionosphere,field-aligned currents(FACs)can also be strengthened in storm times.This study shows the responses of FACs in the plasma sheet boundary layer(PSBL)observed by the Magnetospheric Multiscale(MMS)spacecraft in different phases of a large storm that lasted from May 27,2017,to May 29,2017.Most of the FACs were carried by electrons,and several FACs in the storm time also contained sufficient ion FACs.The FAC magnitudes were larger in the storm than in the quiet period,and those in the main phase were the strongest.In this case,the direction of the FACs in the main phase showed no preference for tailward or earthward,whereas the direction of the FACs in the recovery phase was mostly tailward.The results suggest that the FACs in the PSBL are closely related to the storm and could be driven by activities in the tail region,where the energy transported from the solar wind to the magnetosphere is stored and released as the storm is evolving.Thus,the FACs are an important medium of energy transport between the tail and the ionosphere,and the PSBL is a significant magnetosphere–ionosphere coupling region in the nightside.

The Relief of Plasma Pressure and Generation of Field-Aligned Currents in the Magnetosphere

A combined action of plasma convection and pitch-angle diffusion of electrons and protons leads to the formation of plasma pressure distribution in the magnetosphere on the night side, and, as it is known, steady electric bulk currents are connected to distribution of gas pressure. The divergence of these bulk currents brings about a spatial distribution of field-aligned currents, i.e. magnetospheric sources of ionospheric current. The projection (mapping) of the plasma pressure relief onto the ionosphere corresponds to the form and position of the auroral oval. This projection, like the real oval, executes a motion with a change of the convection electric field, and expands with an enhancement of the field. Knowing the distribution (3D) of the plasma pressure we can determine the places of MHD-compressor and MHD-generators location in the magnetosphere. Unfortunately, direct observations of plasma distribution in the magnetosphere are faced with large difficulties, because pressure must be known everywhere in the plasma sheet at high resolution, which in situ satellites have been unable to provide. Modeling of distribution of plasma pressure (on ~ 3-12 Re) is very important, because the data from multisatellite magnetospheric missions for these purposes would be a very expensive project.

The Pattern of By Deflections Produced from Field-Aligned Currents Earthward of the Activation Source in the Earth’s Magnetosphere

In this investigation effort, we eventually infer that the overall quadrapole pattern of By deflections, in the vicinity of a source in the Earth’s magnetotail, is most likely due to field aligned currents (FACs) and not to Hall currents associated with an X-type collisionless reconnection. This categorically expressed statement is based upon sufficient observational evidence tightly associated with our own suggested model and the preceded works of the same author. Using representative events measured by satellite, our main aim is to describe the nature of the fundamental mechanism determining the polarity of the By deflections associated with intense earthward ionplasma flows. A major finding is that we either observe magnetic flux rope (MFR) like structures (that is, entities having all the morphological features of ropes; i.e., a dipolar signature of Bz occurring simultaneously with peaked By and Btotal deflections) or mere By deflections, however, the sign for all these (Bydeflections) is always determined by the satellite placement in north (positive) or south (negative) plasma sheet. Therefore, the MFR-like structures located earthward of the source are most likely pseudo-MFRs;there is neither a tubular topology nor an axial magnetic field, the By deflections are produced by FACs. According to the presented model, a fundamental concept is that both ions and electrons are simultaneously accelerated at the source site;in turn, the earthward streaming electrons (ions) form a bifurcated electron (ion) FAC just outside the electron diffusion region-EDR (IDR). In this way, inside the IDR (and earthward of the source) positive (negative) By deflections in north (south) plasma sheet (PS) are produced due to FACs, and not to (inward) Hall currents as in the context of an X-line. Moreover, the ions form an “ion jet” within the IDR, while just outside this region they produce positive (negative) By deflections in north (south) PS caused by ion FACs. The ion jet in the IDR is enveloped by the bifurcated electron FAC. Eventually, although the resulting pattern of By deflections, due to both electron and ion FACs, is apparently the same with that resulting from Hall currents (in the X-line model), the underlying natural processes are, however, radically different. Certainly, the dominant “spatial entity” within the IDR is the ion jet-current (and not the Hall-electron current). Additional implications of the ion jets are also discussed.

Effects of current density on microstructure and properties of plasma electrolytic oxidation ceramic coatings formed on 6063 aluminum alloy

Plasma electrolytic oxidation (PEO) ceramic coatings were fabricated in a silicate-based electrolyte with the addition of potassium fluorozirconate (K2ZrF6) on 6063 aluminum alloy, and the effects of current density on microstructure and properties of the PEO coatings were studied. It was found that pore density of the coatings decreased with increasing the current density. The tribological and hardness tests suggested that the ceramic coating produced under the current density of 15 A/dm2showed the best mechanical property, which matched well with the phase analysis. Electrochemical impedance spectroscopy (EIS) and potentiodynamic polarization curves proved that the coating obtained under 15 A/dm2 displayed the best anti-corrosion property, which was directly connected with morphologies of coatings.

Effects of current density on preparation and performance of Al/conductive coating/α-PbO_2-Ce O_2-TiO_2/β-Pb O_2-MnO_2-WC-ZrO_2 composite electrode materials

Al/conductive coating/α-Pb O2-Ce O2-Ti O2/β-PbO 2-MnO 2-WC-Zr O2 composite electrode material was prepared on Al/conductive coating/α-PbO 2-Ce O2-Ti O2 substrate by electrochemical oxidation co-deposition technique. The effects of current density on the chemical composition, electrocatalytic activity, and stability of the composite anode material were investigated by energy dispersive X-ray spectroscopy（EDXS）, anode polarization curves, quasi-stationary polarization（Tafel） curves, electrochemical impedance spectroscopy（EIS）, scanning electron microscopy（SEM）, and X-ray diffraction（XRD）. Results reveal that the composite electrode obtained at 1 A/dm2 possesses the lowest overpotential（0.610 V at 500 A/m2） for oxygen evolution, the best electrocatalytic activity, the longest service life（360 h at 40 °C in 150 g/L H2SO4 solution under 2 A/cm2）, and the lowest cell voltage（2.75 V at 500 A/m2）. Furthermore, with increasing current density, the coating exhibits grain growth and the decrease of content of Mn O2. Only a slight effect on crystalline structure is observed.

A DBRTD with a High PVCR and a Peak Current Density at Room Temperature

AlAs/GaAs/In0.1Ga0.9As/GaAs/AlAs double-barrier resonant tunneling diodes （DBRTDs） grown on a semi-insulated GaAs substrate with molecular beam epitaxy is demonstrated. By sandwiching the In0.1 Ga0.9 As layer between GaAs layers, potential wells beside the two sides of barrier are deepened, resulting in an increase of the peak-to-valley current ratio （PVCR） and a peak current density. A special shape of collector is designed in order to reduce contact resistance and non-uniformity of the current;as a result the total chrrent density in the device is increased. The use of thin barriers is also helpful for the improvement of the PVCR and the peak current density in DBRTDs. The devices exhibit a maximum PVCR of 13.98 and a peak current density of 89kA/cm^2 at room temperature.

Three-D numerical simulation of wind-driven current and density current in the Beibu Gulf

The Casulli's difference scheme was introduced into the three-dimensional ocean model in the present paper, and the wind-driven current and thermohaline current were simulated. The results show that, southwesterly monsoon in summer induces a clockwise circulation in the Beibu Gulf, and the density gradient induces a counter-clockwise one; but the density current is more intense than the wind- driven one in summer, espeially in surface layer. In addition, the northeasterly monsoon in winter in- duces a counter-clockwise circulation. The simulated results don't support the traditional condusion that there is a clockwise circulation in the Beibu Gulf in summer and a counter-clockwise one in winter, but support the statement that a counterclockwise circulation exists in the Beibu Gulf all year round.

A theoretical analysis of the electromigration-induced void morphological evolution under high current density

In this work, analysis of electromigration-induced void morphological evolution in solder interconnects is performed based on mass diffusion theory. The analysis is conducted for three typical experimentally observed void shapes: circular, ellipse, and cardioid. Void morphological evolution is governed by the competition between the electric field and surface capillary force. In the developed model, both the electric field and capillary force on the void's surface are solved analytically. Based on the mass conversation principle, the normal velocity on the void surface during diffusion is obtained. The void morphological evolution behavior is investigated, and a physical model is developed to predict void collapse to a crack or to split into sub-voids under electric current. It is noted that when the electric current is being applied from the horizontal direction, a circular void may either move stably along the electric current direction or collapse to a finger shape, depending on the relative magnitude of the electric current and surface capillary force. However, the elliptical-shaped void will elongate along the electric current direction and finally collapse to the finger shape. On the other hand, the cardioid-shaped void could bifurcate into two sub-voids when the electric current reaches a critical value. The theoretical predictions agree well with the experimental observations.

Effect of the current density on electrodepositing alpha-lead dioxide coating on aluminum substrate

The α-PbO2 electrodes are prepared by anodic electrodeposition on Al/conductive coating electrode from alkaline plumbite solutions in order to investigate the effect of the different current densities on the properties of α-PbO2 electrodes. The physic- ochemical properties of the α-PbO2 electrodes are analyzed by using SEM, EDS, XRD, Tafel plot, linear sweep voltammetry （LSV） and A.C. impedance. A compact and uniform layer of lead dioxide ：）vas obtained at the current density of 3 mA.cm-2. A further increase in current density results in smaller particles with high porosity. EDS and XRD analyses have shown that the PbO2 deposited in alkaline conditions is highly non stoichiometric, and the PbO impurities are formed on the surface layer besides the α-PbO2. The corrosion resistance of α-PbO2 at the low current density is superior to that of the high current density. It can be attributed to a porous layer of deposited films at high current densities in aqueous Zn2＋ 50 g·L^-1, H2SO4 150 When used as anodes for oxygen evolution g·L^-1, the Al/conductive coating/α-PbO2 exhibits lower potential compared to Pb electrode. Al/conductive coating/α-PbO2 electrode with the best electrocatalytic activity was obtained at current density of 1 mA·cm^-2. The lowest roughnest factor was obtained at 1 mA·cm^-2.

Effect of current density on corrosion resistance of micro-arc oxide coatings on magnesium alloy

Oxide coatings were prepared on magnesium alloys in electrolyte solution of Na2SiO3 at different current densities(3,4 and 5 A/cm 2 )with micro-arc oxidation process.X-ray diffractometry(XRD)results show that the oxide coatings formed on magnesium alloys are mainly composed of MgO and MgAl2O4 phases;in addition,the content of MgO increases with increasing the current density.The morphology and surface roughness of the coatings were characterized by confocal laser scanning microscopy (CLSM).The results show that the surface roughness(Ra)decreases with increasing the current density.Moreover,the electrochemical corrosion results prove that the MgO coating produced in the electrolyte Na2SiO3 at current density of 5 A/cm 2 shows the best corrosion resistance.

N‑Doped Graphene‑Decorated NiCo Alloy Coupled with Mesoporous NiCoMoO Nano‑sheet Heterojunction for Enhanced Water Electrolysis Activity at High Current Density

Developing highly effective and stable non-noble metalbased bifunctional catalyst working at high current density is an urgent issue for water electrolysis(WE).Herein,we prepare the N-doped graphene-decorated NiCo alloy coupled with mesoporous NiCoMoO nano-sheet grown on 3D nickel foam(NiCo@C-NiCoMoO/NF)for water splitting.NiCo@C-NiCoMoO/NF exhibits outstanding activity with low overpotentials for hydrogen and oxygen evolution reaction(HER:39/266 mV;OER:260/390 mV)at±10 and±1000 mA cm^(−2).More importantly,in 6.0 M KOH solution at 60℃ for WE,it only requires 1.90 V to reach 1000 mA cm−2 and shows excellent stability for 43 h,exhibiting the potential for actual application.The good performance can be assigned to N-doped graphene-decorated NiCo alloy and mesoporous NiCoMoO nano-sheet,which not only increase the intrinsic activity and expose abundant catalytic activity sites,but also enhance its chemical and mechanical stability.This work thus could provide a promising material for industrial hydrogen production.

Numerical Study on Density Residual Currents of the Bohai Sea in Summer

M 2 tide and density residual currents in the Bohai Sea were examined using the Blumberg and Mellor 3D nonlinear numerical coastal circulation model incorporating Mellor and Yamada level 2.5 turbulent closure model. The tidal results showed good agreement with previous work. The model results indicated that the density residual currents are robust in summer; and that at the transition zone between well-mixed and stratified water, the horizontal velocity is high and the vertical velocity is positive.

Experimental Study of Current Loss of Stainless Steel Magnetically Insulated Transmission Line with Current Density at MA/cm Level

A magnetically insulated transmission line （MITL） is used to transmit high power electric pulses in large pulse power systems. However, current loss is unavoidable, especially when the current density is up to 1 MA/cm. In the paper, the current loss of an MITL made of stainless steel, which is usually used in large pulse power generators, is experimentally studied, and possible mechanisms to explain the current loss of the MITL are analyzed and discussed. From the experimental results, the relationship between loss current density and input current density follows approximately a power law. The loss is also related to the configuration of the MITL.

Numerical Simulation of Current Density Distribution in Keyhole Double-Sided Arc Welding

In the double-sided arc welding system (DSAW) composing of PAW+TIG arcs, the PAW arc is guided by the TIG arc so that the current mostly flows through the direction of the workpiece thickness and the penetration is greatly improved. To analyze the current density distribution in DSAW is beneficial to understanding of this process. Considering all kinds of dynamic factors acting on the weldpool, this paper discusses firstly the surface deformation of the weldpool and the keyhole formation in PAW+TIG DSAW process on the basis of the magnetohydrodynamic theory and variation principles. Hence, a model of the current density distribution is developed. Through numerical simulation, the current density distribution in PAW+TIG DSAW process is quantitatively analyzed. It shows that the minimal radius of keyhole formed in PAW+TIG DSAW process is 0.5 mm and 89.5 percent of current flows through the keyhole.

Determination of arc pressure pool surface in and current density on the molten plasma arc welding

A unified numerical model is developed to couple the plasma arc, weld pool and keyhole in a self consistent way. The plasma arc/anode interface and the melt/solid interface are treated specially, the VOF method is used to trace the moving keyhole wall, and the fluid flow and heat transfer in both the plasma arc and weld pool are numerically simulated. The distributions of current density and arc pressure on the weld pool surface during the keyhole formation process are analyzed using the coupled model. The predicted arc pressure and current density are compared with the experimentally measured results, and both are in good agreement.

Electroplating of Ni/Co–pumice multilayer nanocomposite coatings: Effect of current density on crystal texture transformations and corrosion behavior

The present paper aims to investigate the influence of the current density in the electroplating process on the microstructure, crystal texture transformations, and corrosion behavior of Ni/Co pumice multilayer nanocomposite coatings. The Ni/Co pumice composite coatings were prepared by deposition of Ni, followed by the simultaneous deposition of pumice nanoparticles (NPs) in a Co matrix via an electroplating process at various current densities. Afterward, the morphology, size, topography, and crystal texture of the obtained samples were investigated. Furthermore, electrochemical methods were used to investigate the corrosion behavior of the produced coatings in a solution of 3.5wt% NaCl. The results indicated that increasing the plating current density changed the mechanism of coating growth from the cell state to the column state, in- creased the coating thickness, roughness, and texture coefficient (TC) of the Co (203) plane, and reduced the amount of pumice NPs incorporated into the Ni/Co pumice composite. The electrochemical results also indicated that increasing the current density enhanced the corrosion resistance of the Ni/Co pumice composite.

Reconstruction of Current Density Distribution in Weld Area During Resistance Spot Welding of Aluminum Alloy Based on Magnetic Field

Magnetic flux density around the weld area was used to reconstruct the current density distribution during resistance spot welding(RSW) of aluminum alloy according to inverse problem theory. A current-magnetic field model was established and the conjugate gradient method was used to solve this model. The results showed that the current density was low at the center of nugget while high on the edge of nugget. Moreover, the welding time of 30ms—60 ms is a key period for nucleation. The current density distribution can reflect whether the weld nugget is formed or splashed, therefore it has the potential to monitor the weld quality of RSW.