Hydrogen spillover bridged dual nano-islands triggered by built-in electric field for efficient and robust alkaline hydrogen evolution at ampere-level current density

Employing the alkaline water electrolysis system to generate hydrogen holds great prospects but still poses significant challenges,particularly for the construction of hydrogen evolution reaction(HER)catalysts operating at ampere-level current density.Herein,the unique Ru and RuP_(2)dual nano-islands are deliberately implanted on N-doped carbon substrate(denoted as Ru-RuP_(2)/NC),in which a built-in electric field(BEF)is spontaneously generated between Ru-RuP_(2)dual nano-islands driven by their work function difference.Experimental and theoretical results unveil that such constructed BEF could serve as the driving force for triggering fast hydrogen spillover process on bridged Ru-RuP_(2)dual nano-islands,which could invalidate the inhibitory effect of high hydrogen coverage at ampere-level current density,and synchronously speed up the water dissociation on Ru nano-islands and hydrogen adsorption/desorption on RuP_(2)nano-islands through hydrogen spillover process.As a result,the Ru-RuP_(2)/NC affords an ultra-low overpotential of 218 mV to achieve 1.0 A·cm^(−2)along with the superior stability over 1000 h,holding the great promising prospect in practical applications at ampere-level current density.More importantly,this work is the first to advance the scientific understanding of the relationship between the constructed BEF and hydrogen spillover process,which could be enlightening for the rational design of the cost-effective alkaline HER catalysts at ampere-level current density.

Effect of high density pulse electric current on solidification structure of low temperature melt of A356 alloy

The effect of high density pulse electric current (HDPEC) on the solidification structure of the low temperature melt(LTM) of commercial A356 alloy was investigated. In the experiments, the HDPEC was discharged in the LTM (953?K, 903?K and 873?K). By the control experiments, the results showed that the solidification structure of the LTM of A356 alloy is refined apparently when the HDPEC is discharged in low temperature melt. However, the holding time of melt treated has an adverse effect on the solidification structure. The longer the holding time of the melt treated with HDPEC, the coarser the microstructure. With the same discharge voltage, the lower the temperature of LTM, the more obscure the refinement of solidification structure. Finally, the mechanism of microstructure refining by HDPEC was analyzed.

Use of 3-D magnetic resonance electrical impedance tomography in detecting human cerebral stroke: a simulation study

We have developed a new three dimensional (3-D) conductivity imaging approach and have used it to detect human brain conductivity changes corresponding to acute cerebral stroke. The proposed Magnetic Resonance Electrical Impedance Tomography (MREIT) approach is based on the J-Substitution algorithm and is expanded to imaging 3-D subject conductivity distribution changes. Computer simulation studies have been conducted to evaluate the present MREIT imaging approach. Simulations of both types of cerebral stroke, hemorrhagic stroke and ischemic stroke, were performed on a four-sphere head model. Simulation results showed that the correlation coefficient (CC) and relative error (RE) between target and estimated conductivity distributions were 0.9245±0.0068 and 8.9997%±0.0084%, for hemorrhagic stroke, and 0.6748±0.0197 and 8.8986%±0.0089%, for ischemic stroke, when the SNR (signal-to-noise radio) of added GWN (Gaussian White Noise) was 40. The convergence characteristic was also evaluated according to the changes of CC and RE with different iteration numbers. The CC increases and RE decreases monotonously with the increasing number of iterations. The present simulation results show the feasibility of the proposed 3-D MREIT approach in hemorrhagic and ischemic stroke detection and suggest that the method may become a useful alternative in clinical diagnosis of acute cerebral stroke in humans.

Impact of Ion Current on Total Electric Field Measurement Under HVDC Transmission Line

The total electric field(TEF) at ground level induced by high-voltage direct current(HVDC) overhead transmission lines is one of the important indexes for evaluating the lines' electromagnetic environment.Based on analyzing the existing TEF sensors and the measurement principle of ion-current density,the influence from ions on TEF measurements is quantitively studied.The results show that the ions generated by the corona from a HVDC transmission line in operation cause errors in the measurement of TEF.This error is determined through analyzing the component of total measuring current on the filed mill's sensing electrode: if no appropriate approach taken,the maximum measurement error reaches up to 4.3%.Furthermore,a method that can eliminate such error,and hence improve the accuracy of TEF sensors is designed.

High-Frequency Electric Field Induced Nonlinear Electron Transport in Chiral Carbon Nanotubes

We investigate theoretically the high frequency complex conductivity in carbon nanotubes that are stimulated axially by a strong inhomogeneous electric field of the form E(t)=E0+E1cos(ωt). Using the kinetic approach based on Boltzmann’s transport equation with constant relaxation time approximation and the energy spectrum of the electron in the tight-binding approximation, together with Bhatnagar-Gross-Krook collision integral, we predict high-frequency nonlinear effects along the axial and the circumferential directions of the carbon nanotubes that may be useful for the generation of high frequency radiation in the carbon nanotubes.

Migration Behavior of Impurity Iron in Silicon Melt Under Pulsed Electric Current

The impurity iron in silicon material will seriously affect the photoelectric conversion efficiency of silicon solar cells.However,the traditional silicon purification method has the disadvantages of long cycle,high energy consumption and serious pollution.In this study,an efficient and green pulsed electric current purification technology is proposed.The electromigration effect of iron elements,the current density gradient driving of iron phase,and the gravity of iron phase all affect the migration behavior of iron phase in silicon melt under pulsed electric current.Regardless of the depth of electrode insertion into the silicon melt,the solubility of iron in silicon decreases under the pulsed electric current,which helps to form the iron phase.At the same time,the iron phase tends to sink toward the bottom under the influence of gravity.When the electrode is shallowly inserted,a non-uniform electric field is formed in the silicon melt,and the iron phase is mainly driven by the current density gradient to accelerate sink toward the bottom.When the electrode is fully inserted,an approximately uniform electric field is formed in the silicon melt,and iron elements are preferentially migrated to the cathode by electromigration,forming iron phase sinking at the cathode.The study of impurity iron migration behavior in silicon melt under pulsed electric current provides a new approach for the purification of polycrystalline silicon.

Electro-hydrodynamic Simulation of Wire-plate Corona Discharge

To simulate the electro-hydrodynamics of wire-plate corona discharge at different voltages accurately,a simulation method,which relates the definite radius and initial velocity of a jet source to the amplitude of discharge voltage,is developed.Firstly,a model of the electro-hydrodynamics is established by the Matlab software using the governing equations discretized with the finite difference method.Secondly,the electric field strength and current density are simulated and the radius and initial velocity of a jet source at different voltages are determined.Finally,the discharge electro-hydrodynamics is simulated using the determined boundary conditions.Compared with using a conventional method,using the proposed method can obtain a wind velocity with smaller errors from the experimental and theoretical wind velocities: the errors between simulated wind velocity and its theoretical counter part at 45 kV and 50 kV decrease from 9% and 6.25% to 1.7% and 1.56%,respectively.Thus,the proposed method is feasible for the existing discharge models.

External Electric Field Effect on Electrons Transport in Carbon Nanotubes

We consider a simple model of carbon nanotubes (CNTs) subject to external electric field E(t). Using a tight-binding approximation for the description of energy bands of CNTs, together with the standard Boltzmann transport equation and constant relaxation time, we predict the effect of self-induced transparency and absolute negative conductivity. The predicted effects may be useful in diagnostics of carbon nanotubes as well as in the amplification and efficiency conversion of electromagnetic signals.

Molybdenum Electrodes Applied in Electric Melting Furnace

The conditions and points for attentions of molybdenum electrode, which used in glass melting furnace, are introduced. Problems in corrosion of molybdenum electrodes are analyzed through the glass components, temperature and current density, and how to eliminate bubble formation on the process. At last, the specific requests of the applications of molybdenum electrode in glass industry are presented.

舰艇水下腐蚀静电场计算及影响因素仿真分析

为了进一步分析影响舰船电场的不同因素,提高舰艇水下静电场仿真分析中电偶极子建模方法的准确性,研究产生舰艇水下腐蚀静电场的腐蚀电化学原理和特性,从腐蚀电流密度的角度推导船体-螺旋桨电偶腐蚀电流表达式,并利用镜像法求解出了空气-海水二层模型下水平和垂直电偶极子电场解析式。建立基于舰艇腐蚀电流电偶极子的电场解析模型,在此基础上利用数值仿真对一中型舰艇水下50 m测线上的电场进行分析。结果表明:在设定变化范围内,船体腐蚀电位、螺旋桨腐蚀电位、船体浸水面积、螺旋桨浸水面积、海水温度、海水电导率对舰艇水下腐蚀静电场的影响程度分别约为29%、23%、53%、82%、30%和67%。仿真结果和电场解析模型可以为进一步研究舰艇水下腐蚀静电场特征及防护方法提供有力的理论支撑。

高密度脉冲电流对过共晶Al-Si合金凝固组织的影响

研究了高密度脉冲电流对过共晶Al 19Si合金凝固组织的影响。结果表明 :未经任何处理的试样凝固组织中含有大量的长杆状初生Si,其长宽比较大 ,且共晶Si尺寸较大 ;而经过高密度脉冲电流处理后 ,凝固组织中初生Si转变为块状 ,长宽比显著减小 ,共晶Si呈短杆状 ,尺寸较小 ,另外在试样的局部存在初生Si晶粒破碎现象 。

碳纳米管-银-石墨复合材料的电磨损性能

采用粉末冶金工艺制备碳纳米管—银—石墨复合材料,初压压力200 MPa,在H_2保护气氛下烧结并保温1h,复压压力400 MPa制得复合材料,研究电流密度(0～25 A/cm^2)对碳纳米管—银—石墨复合材料摩擦磨损性能的影响。结果表明：随着电流密度的增大,电磨损过程中的发热量增大,粘着磨损加剧,润滑膜遭到破坏,导致复合材料的摩擦因数、磨损量增大。比较正、负极电刷磨损量发现,接触表面理化反应和金属转移的存在,导致正刷磨损量大于负刷磨损量：正刷磨损量随电流密度增大而成倍增长,负刷磨损量与电流密度关系不明显,电流密度越大磨损极性的差异越明显。

4H-SiC肖特基势垒二极管伏-安特性的解析模型

在分析 4H SiC肖特基势垒二极管正向电流热电子发射理论的基础上 ,计算了肖特基势垒高度eff和串联电阻Ron.通过对反向电流各种输运机制的分析 ,提出了一种计算反向电流密度的理论模型 .计算结果与实验数据的比较表明 ,隧道效应是反向电流的主要输运机理 .

特高压直流输电线路离子流场的有限元-积分法计算

针对特高压直流输电线的地面电场和离子流密度的计算问题,采用有限元-积分方法,对双极离子流场的控制方程进行求解,同时还对空间电荷密度初值进行了改进。通过计算,发现该方法能较快地获得稳定的数值解。通过采用该方法对±400kV的直流线路进行了比对计算,验证了该算法的有效性。将该方法应用于实际的±800kV直流输电线路,对地面合成电场和离子流密度进行了计算,分析了导线对地高度、极间距、正负极起晕情况不同以及避雷线对地面合成电场和离子流密度的影响。结果显示随导线高度升高和极间距减小,地面的最大电场强度和离子流密度随之减小。在正、负极起晕不同时,负极导线下面的合成电场和离子流密度的最大值比正极大。计算中,考虑避雷线会增大地面的合成场强和离子流密度,但是不明显。

三相变压器两侧绕组匝间短路电磁特性研究

为了研究变压器匝间短路时电流随匝数的变化规律,首先对变压器匝间短路时的电流进行了解析推导。然后,建立变压器匝间短路故障前后的等效电路,推导两侧电流随短路匝数变化的公式,并通过自检电阻的不同状态进行自我验证和推广应用。最后,采用商业软件Ansys对实际变压器进行正常运行及匝间短路时电流与磁场的仿真计算,与解析法电流公式对比,验证了解析公式及数值计算的准确性。研究结果可为变压器匝间短路的检测与分析提供参考。

直流电流时效对Cu-0.33Cr-0.06Zr合金显微硬度的影响

对Cu-0.33Cr-0.06Zr合金先固溶再冷变形,进行了450℃下不同时效时间及不同电流密度的时效试验。研究了不同电流密度对Cu-0.33Cr-0.06Zr合金时效后硬度的影响。研究结果表明:电流密度越大,合金到达硬度峰值的时间越短。合金在电流密度为400 A·cm-2下,时效0.25 h就到达峰值227HV。对比无电流下时效,大密度的直流电流在时效初期能大大提高合金的硬度,时效后期则会降低合金的硬度。

研究UV-LIGA微电铸电极过程的交流阻抗法

在给定的电铸液组分和工艺路线下,运用交流阻抗法研究了微电铸镍结构的电极过程动力学特性。建立了微电铸体系的等效电路,根据实验获得的交流阻抗图和电阻电抗频率响应,分析了搅拌、整平剂对微电铸体系交流阻抗的影响,计算了电极过程的交换电流密度。结果表明,加入十二烷基硫酸钠整平剂数量存在一个使交流阻抗最小的最佳值,大小为3 g/L,在有搅拌、加入最佳量的整平剂时,体系电极过程的交换电流密度为0.171 A/dm2。在微电铸过程中有搅拌、加入适量整平剂使电铸液交流阻抗下降,阴极电流效率提高,可以改善微电铸镍结构的表面性能、致密度和高度均匀性。

电絮凝法处理垃圾中转站渗滤液的效能及条件优化

采用电絮凝法处理垃圾中转站的渗滤液,分别考察了阳极材料、电流密度、极板间距、反应时间、初始pH及电解质过硫酸钾对渗滤液COD去除率的影响。结果表明:在最佳反应条件下,即采用铁板为阳极材料、电流密度为0.042 A/cm^(2)、极板间距为1 cm、初始pH为7,电絮凝反应3 h后,可将渗滤液COD浓度从23525 mg/L降低至10619 mg/L,其去除率可达54.86%。投加电解质过硫酸钾与电絮凝协同作用对渗滤液进行预处理,可有效强化电絮凝反应对渗滤液COD的去除效果,反应初期COD去除率相对提高了6.68%;但当电解时间大于3 h后,过硫酸钾的强化作用逐渐减弱。

不同工艺条件对柔性低温多晶硅薄膜晶体管性能影响

为了探究不同工艺对柔性低温多晶硅薄膜晶体管性能的影响,对比了3种不同工艺薄膜晶体管的电学特性和陷阱特性。首先,通过瞬态电流法研究陷阱,运用陷阱对载流子的捕获和释放的特点测量得到瞬态电流曲线,通过分别改变栅压和漏压并结合不同温度的陷阱去俘获峰值曲线提取的激活能分析得到不同俘获过程所对应的不同位置的3种陷阱。其次,用仪器测量器件的I-V特性曲线,提取器件的阈值电压V_(TH)、亚阈值摆幅S和迁移率μ进行比对分析。结果显示,样品A2的工艺改善了膜质,降低了器件的阈值电压和关态漏电流,同时降低了栅氧化层的陷阱密度;样品A4的工艺填补了界面和沟道内的悬挂键,优化了器件的迁移率和亚阈值摆幅,同时降低了界面和晶界的陷阱密度。

电铸自支撑金刚石-镍复合膜的制备(英文)

用电铸方法，采用低应力电镀液，制备出了自支撑金刚石-镍复合膜。电镀液PH值3．84．2，温度40～60℃，阳极与阴极间距100～150mm。用扫描电镜（SEM）和X射线衍射（XRD）方法检测了复合膜的表面形貌、晶体显微结构和复合膜中金刚石颗粒的分布情况。结果表明：阴极电流密度对自支撑金刚石-镍复合膜的品质影响很大，当阴极电流密度从1．3A／dm^2增加到3．3A／dm^3时，复合膜的显微应变从0．36％减小到0．28％；随着阴极电流密度的增加，复合膜中金刚石颗粒的含量增加。