Strong electronic coupling of CoNi and N-doped-carbon for efficient urea-assisted H2 production at a large current density

Exploiting efficient urea oxidation reaction(UOR)and hydrogen evolution reaction(HER)catalysts are significant for energy-saving H2 production through urea-assisted water electrolysis,but it is still challenging.Herein,carbon-encapsulated CoNi coupled with CoNiMoO(CoNi@CN-CoNiMoO)is prepared by solvothermal method and calcination to enhance the activity/stability of urea-assisted water electrolysis at large current density.It exhibits good activity for UOR(E10/1,000=1.29/1.40 V)and HER(E-10/-1000=-45/-245 mV)in 1.0 M KOH+0.5 M urea solution.For the UOR||HER system,CoNi@CN-CoNiMoO only needs 1.58 V at 500 mA cm-2 and shows good stability.Density functional theory calculation suggests that the strong electronic interaction at the interface between NiCo alloy and N-doping-carbon layers can optimize the adsorption/desorption energy of UOR/HER intermediates and accelerate the water dissociation,which can expedite urea decomposition and Volmer step,thus increasing the UOR and HER activity,respectively.This work provides a new solution to design UOR/HER catalysts for H2 production through urea-assisted water electrolysis.

A CAD oriented quasi-analytical large-signal drain current model for 4H-SiC MESFETs

This paper reports that a 4H-SiC MESFET （Metal Semiconductor Field Effect Transistor） large signal drain current model based on physical expressions has been developed to be used in CAD tools. The form of drain current model is based on semi-empirical MESFET model, and all parameters in this model are determined by physical parameters of 4H-SiC MESFET. The verification of the present model embedded in CAD tools is made, which shows a good agreement with measured data of large signal DC I-V characteristics, PAE （power added efficiency）, output power and gain.

Controllable synthesis of a self-assembled ultralow Ru,Ni-doped Fe_(2)O_(3) lily as a bifunctional electrocatalyst for large-current-density alkaline seawater electrolysis

Highly efficient and stable bifunctional electrocatalysts that can be used for large-current-density electrolysis of alkaline seawater are highly desirable for carbon-neutral economies,but their facile and controllable synthesis remains a challenge.Here,self-assembled ultralow Ru,Ni-doped Fe_(2)O_(3) with a lily shaped morphology was synthesized on iron foam(RuNi-Fe_(2)O_(3)/IF)via a facile one-step hydrothermal process,in which the intact lily shaped RuNi-Fe_(2)O_(3)/IF was obtained by adjusting the ratio of Ru/Ni.Benefitting from the Ru/Ni chemical substitution,the as-synthesized RuNi-Fe_(2)O_(3)/IF can act as free-standing dual-function electrodes that are applied to electrocatalysis for the hydrogen evolution(HER)and oxygen evolution reactions(OER)in 1.0 mol L^(-1) KOH,requiring an overpotential of 75.0 mV to drive 100 mA cm^(-2) for HER and 329.0 mV for OER.Moreover,the overall water splitting catalyzed by RuNi-Fe_(2)O_(3)/IF only demands ultralow cell voltages of 1.66 and 1.73 V to drive 100 mA cm^(-2) in 1.0 mol L^(-1) KOH and 1.0 mol L^(-1) KOH seawater electrolytes,respectively.The electrodes show remarkable long-term durability,maintaining current densities exceeding 100 mA cm^(-2) for more than 100 h and thus outperforming the two-electrode system composed of noble catalysts.This work provides an efficient,economical method to synthesize self-standing bifunctional electrodes for large-current-density alkaline seawater electrolysis,which is of significant importance for ecological protection and energy exploitation.

Electrical Performance Study of a Large Area Multicrystalline Silicon Solar Cell Using a Current Shunt and a Micropotentiometer

In this paper, a new technique using a Current Shunt and a Micropotentiometer has been used to study the electrical performance of a large area multicrystalline silicon solar cell at outdoor conditions. The electrical performance is mainly described by measuring both cell short circuit current and open circuit voltage. The measurements of this cell by using multimeters suffer from some problems because the cell has high current intensity with low output voltage. So, the solar cell short circuit current values are obtained by measuring the voltage developed across a known resistance Current Shunt. Samples of the obtained current values are accurately calibrated by using a Micropotentiometer (μpot) thermal element (TE) to validate this new measuring technique. Moreover, the solar cell open circuit voltage has been measured. Besides, the cell output power has been calculated and can be correlated with the measured incident radiation.

Temperature Effects on the Electrical Performance of Large Area Multicrystalline Silicon Solar Cells Using the Current Shunt Measuring Technique

The temperature effects on the electrical performance of a large area multicrystalline silicon solar cell with back-contact technology have been studied in a desert area under ambient conditions using the current shunt measuring technique. Therefore, most of the problems encountered with traditional measuring techniques are avoided. The temperature dependency of the current shunt from 5oC up to 50oC has been investigated. Its temperature coefficient proves to be negligible which means that the temperature dependency of the solar cell is completely independent of the current shunt. The solar module installed in a tilted position at the optimum angle of the location, has been tested in two different seasons (winter and summer). The obtained solar cell short circuit current, open circuit voltage and output power are correlated with the measured incident radiation in both seasons and all results are discussed.

Study on scour around vertical large-size cylinder base due to combined action of wave and current

Based on the mechanism of local scour around vertical large-sized cylinder due to combined action of wave and current,the sour morphology,scour process and the maximum scour depth around the cylinders are studied experimentally.The influence of various ocean environmental parameters on local scour around the cylinder is considered in physical model test.The experimental results indicate that the principal effect factors on the scour in fine-sand seabed are wave height,wavelength,current velocity,ratio of diameter to wavelength and ratio of depth to wavelength when the ratio of cylinder diameter to wavelength is from 0.2 to 0.8.In this paper,dimensional analysis theory is utilized to establish a theoretical equation for forecasting maximum scour depth around large-sized round cylinder base due to the combined action of wave and current.The results computed with the theoretical equation are compared with the experimental results,and found to be in good consistency.The results in this studies can be used to estimate the maximum sour depth around analogous structures.

Applied the Large Scale Particle Image Velocimetry Technique for Measurement the Velocity of Gravity Currents in the Laboratory

This study includes a series of laboratory experiments for investigated the gravity current of fresh water with density ρ-?ρ, and initial speed u0 upon the free surface of an ambient liquid (salty water) with density ρ at rest in a basin. It’s have been presented to illuminate the dominant flow and transport phenomena in the presence of river, stream and wetland ecology, stream corridor restoration, in the case of accidental pollution spills. The characterized of the local kinematic field, i.e. the local velocity and vorticity fields, the measurement methods include particle image velocimetry (PIV) at the water surface using a technique similar to large scale of particle image velocimetry (LSPIV).

Saturation Ion Current Densities in Inductively Coupled Hydrogen Plasma Produced by Large-Power Radio Frequency Generator

An experimental investigation of the saturation ion current densities （Jions） in hydrogen inductively coupled plasma （ICP） produced by a large-power （2-32 kW） radio frequency （RF） generator is reported, then some reasonable explanations are given out. With the increase of RF power, the experimental results show three stages： in the first stage （2-14 kW）, the electron temperature will rise with the increase of RF power in the ICP, thus, the Jions increases continually as the electron temperature rises in the ICP. In the second stage （14 20 kW）, as some H- ions lead to the mutual neutralization （MN）, the slope of Jio^s variation firstly decreases then increases. In the third stage （20-32 kW）, both the electronic detachment （ED） and the associative detachment （AD） in the ICP result in the destruction of H- ions, therefore, the increased amplitude of the Jions in the third stage is weaker than the one in the first stage. In addition, with the equivalent transformer model, we successfully Explain that the Jions at different radial locations in ICP has the same rule. Finally, it is found that the Jions has nothing to do with the outer/inner puffing gas pressure ratio, which is attributed to the high-speed movement of hydrogen molecules.

Numerical multi-physical optimization of operating condition and current collecting setup for large-area solid oxide fuel cells

Due to the depletion of traditional fossil fuels and the aggravation of related environmental problems,hydrogen energy is gaining more attention all over the world.Solid oxide fuel cell(SOFC)is a promising power generation technology operating on hydrogen with a high efficiency.To further boost the power output of a single cell and thus a single stack,increasing the cell area is an effective route.However,it was recently found that further increasing the effective area of an SOFC single cell with a flat-tubular structure and symmetric double-sided cathodes would result in a lower areal performance.In this work,a multi-physical model is built to study the effect of the effective area on the cell performance.The distribution of different physical fields is systematically analyzed.Optimization of the cell performance is also pursued by systematically tuning the cell operating condition and the current collection setup.An improvement of 42%is revealed by modifying the inlet gas flow rates and by enhancing the current collection.In the future,optimization of cell geometry will be performed to improve the homogeneity of different physical fields and thus to improve the stability of the cell.

Heterophase junction engineering-induced Co spin-state modulation of CoSe_(2) for large-current hydrogen evolution reaction

Efficient electrocatalysts are vital to large-current hydrogen production in commercial water splitting for green energy generation.Herein,a novel heterophase engineering strategy is described to produce polymorphic CoSe_(2)electrocatalysts.The composition of the electrocatalysts consisting of both cubic CoSe_(2)(c-CoSe_(2))and orthorhombic CoSe_(2)(o-CoSe_(2))phases can be controlled precisely.Our results demonstrate that junction-induced spin-state modulation of Co atoms enhances the adsorption of intermediates and accelerates charge transfer resulting in superior large-current hydrogen evolution reaction(HER)properties.Specifically,the CoSe_(2)based heterophase catalyst with the optimal c-CoSe_(2)content requires an overpotential of merely 240 mV to achieve 1,000 mA·cm^(-2)as well as a Tafel slope of 50.4 mV·dec^(-1).Furthermore,the electrocatalyst can maintain a large current density of 1,500 mA·cm^(-2)for over 320 h without decay.The results reveal the advantages and potential of heterophase junction engineering pertaining to design and fabrication of low-cost transition metal catalysts for large-current water splitting.

Investigation of Ancient and Large Tree Resources in Green Spaces of Urban Parks: A Case Study of Yunqizhujing Park in Hangzhou, China

Conservation of ancient and large trees in domestic and overseas cities was compared, ancient and large trees were regarded as important cultural relics playing an important role in optimizing urban natural environment and enriching urban humanistic and natural landscapes, and they were also important contents of urban garden works symbolizing urban parks. A case study was carried out Yunqizhujing Park to study conservation of ancient and large trees in park green spaces of Hangzhou City, solutions to current problems were proposed, and constructive suggestions were given for the conservation of ancient and large trees in urban park green spaces.

Observational Features of Large-Scale Structures as Revealed by the Catastrophe Model of Solar Eruptions

Large-scale magnetic structures are the main carrier of major eruptions in the solar atmosphere. These structures are rooted in the photosphere and are driven by the unceasing motion of the photospheric material through a series of equilibrium configurations. The motion brings energy into the coronal magnetic field until the system ceases to be in equilibrium. The catastrophe theory for solar eruptions indicates that loss of mechanical equilibrium constitutes the main trigger mechanism of major eruptions, usually shown up as solar flares, eruptive prominences, and coronal mass ejections （CMEs）. Magnetic reconnection which takes place at the very beginning of the eruption as a result of plasma instabilities/turbulence inside the current sheet, converts magnetic energy into heating and kinetic energy that are responsible for solar flares, and for accelerating both plasma ejecta （flows and CMEs） and energetic particles. Various manifestations are thus related to one another, and the physics behind these relationships is catastrophe and magnetic reconnection. This work reports on recent progress in both theoretical research and observations on eruptive phenomena showing the above manifestations. We start by displaying the properties of large-scale structures in the corona and the related magnetic fields prior to an eruption, and show various morphological features of the disrupting magnetic fields. Then, in the framework of the catastrophe theory, we look into the physics behind those features investigated in a succession of previous works, and discuss the approaches they used.

波流环境中多孔射流三维数值模拟

建立了波流环境中多孔射流的三维大涡数学模型,探讨了波流共同作用下多孔射流的扩散和稀释机制,分析了孔间距对双孔射流、射流与环境水体相互作用的影响,并给出了最优相对孔间距。模拟结果表明:在波谷相位时刻,由于横流与波浪相互作用强烈,流场内的三维涡旋结构丰富、尺度较大、数目众多,有利于射流与环境水体、射流与射流之间的掺混,这是波流环境比单一横流环境中多孔射流运动扩散效果更佳的主要原因;随着孔间距的增大,双孔射流之间的相互作用慢慢削弱,而射流与环境水体之间的相互作用却在不断增强;双孔射流在孔间距为7.0倍管口直径时扩散效果最好。

模块化高压大容量DC/DC变换器综述

随着新能源发电占比增加和电网规模的不断扩大,直流输电系统的容量不断提升,含有不同电压等级的直流电网是未来发展的必然趋势。在此背景下,DC/DC变换器作为直流电网关键设备,在多电压等级互联场景中发挥着重要作用。文中首先对已有的模块化高压大容量DC/DC变换器进行归纳、分类和比较,然后阐述了目前模块化高压大容量DC/DC变换器的拓扑结构、工作原理与特点,并针对其特点提出了不同变换器的适用场景,最后对未来的研究方向提出了建议。

台风-浪-流耦合作用超大浮体水弹性响应分析方法

海上机场超大浮体结构在台风等极端海洋环境下的动态响应准确预测是保障其安全性能的关键前提,其难点在于准确构建中/小尺度复杂流场与浮体结构的流固耦合计算模型。本文提出了一种基于中/小尺度嵌套的海上机场超大浮体水弹性响应分析方法,二次开发实现了台风-浪-流耦合模拟,分析了超强台风“莫兰蒂”途经海上机场超大浮体全过程台风-浪-流时空演变规律;采用中/小尺度流场嵌套技术计算水动力和气动力,代入结构动力学方程进行双向迭代解耦求解;通过算例分析了台风-浪-流耦合作用下浮体结构水弹性响应及影响机制。研究表明:本文提出的方法能够有效地预测此类极端环境下超大浮体结构水弹性响应。

我国大中型水闸安全鉴定现状与对策建议

根据“十四五”以来水闸安全运行专项检查和现状调研资料,梳理总结了我国大中型水闸安全鉴定现状、存在问题及成因。探讨了《水闸安全鉴定管理办法》及其配套技术标准《水闸安全评价导则》存在的不足,其中部分条文依据的规范性文件和技术标准已不适应新阶段水利高质量发展要求,影响到水闸安全鉴定成效。基于此,从修订完善制度标准、加大经费保障力度、严格检查监督、积极推进水闸除险加固等方面,提出水闸安全鉴定制度和技术标准修订以及管理工作方面的对策建议。

Fe稳固的FeOOH@NiOOH电催化剂的大电流极化设计与析氧研究

电解水技术是制取高纯度氢气的有效途径,为传统的氢气生产提供了一种可持续的替代方案.其中,开发性能优异的电催化材料是降低电解水制氢成本的关键.析氧反应(OER)由于涉及多个电子转移而导致的动力学缓慢,是克服高过电位的主要挑战.镍铁羟基/氢氧化物(NiFe(oxy)hydroxides)是近期研究的热点,其在碱性条件下具有极低的OER过电位,部分材料性能甚至超过了贵金属基催化剂,如IrO_(2)和RuO_(2).然而,NiFe(oxy)hydroxides的长期催化稳定性,尤其是在大电流下的长期催化稳定性,成为限制其实际应用的主要问题,这主要是由于铁元素的严重流失导致的.因此,如何有效控制和利用电化学溶解/沉积动力学成为稳定铁位点的关键.为克服该挑战,本文提出了一种大电流极化重构方法来固定活性铁位点.通过在大电流(1.5 A cm^(-2))下对材料进行表面快速极化重构,成功制备了FeOOH@NiOOH(eFNO_(L))电催化剂.eFNO_(L)不仅具有稳定的铁位点,还暴露出高指数晶面,因此eFNO_(L)同时展现出较好的OER催化活性和稳定性.同时,密度泛函理论计算结果表明,与具有低指数晶面的FeNiOOH相比,大电流极化工程制备的分相eFNO_(L)对铁位点表现出更高的结合能,可以有效抑制OER过程中的铁流失,且高指数晶面在改变速率决定步骤和减少吸附能垒上具有更大的优势.电化学测试结果表明,经过优化后的eFNO_(L)催化剂在产生100和500 mA cm^(-2)大电流密度仅需234和27 mV的过电位,并且具有较小的Tafel斜率(35.2 mV dec^(-1)).由于铁位点结合能的提高,eFNO_(L)催化剂在500 mA cm^(-2)的电流密度下能够稳定催化超过100 h,且仅有1.5%的性能衰减,优于近期报道的大多数镍铁基OER催化剂.综上,本文为开发高活性和高稳定性能的催化剂提供了一种有效的大电流电化学重构策略,在电解水制氢领域实现其工业化的大规模应用方面显示出巨大潜力,有望降低可持续电解水制氢成本.

大型发电机定子接地故障柔性融合消弧方法

大型发电机发生定子单相接地故障可能会产生电弧,导致铁心烧损,甚至引发火灾等严重事故,提出一种柔性融合消弧方法,通过并行控制中性点电压和变流器注入电流,实现接地故障电流抑制和可靠消弧。现有发电机定子单相接地柔性消弧方法在低阻或高阻的情况下消弧效果不佳,所提方法考虑了发电机的定子阻抗和定子并联分支数,适用于不同的发电机,在不同接地故障过渡电阻、不同故障位置等情况下,均能够将接地故障电流快速抑制到安全范围内。Matlab/Simulink仿真验证了所提方法的有效性。

Nonlinear Current-Voltage Characteristics and Electroluminescence of cBN Crystal

The current-voltage（I-V） characteristics of cBN crystal sandwiched between two metallic electrodes are measured and found to be nonlinear. Over 20 samples are measured at room temperature with various electrodes, and the resulting curves are all similar in shape. When a voltage of about 560V is applied to the cBN crystal, the emitted light is visible to the naked eye in a dark room. We explain these phenomena by the space charge limited current and the electronic transition between the X and Г valleys of the conduction band.

高速大像素CMOS图像传感器中钳位光电二极管形状设计的研究进展

采用钳位光电二极管(PPD)的CMOS图像传感器,由于其优异的性能,已成为图像传感领域中占主导地位的技术。然而,更大尺寸PPD的应用在电荷传输速度和效率方面存在挑战,特别是在微光、高速探测的场景中,传统的像素设计难以满足必要的性能标准。一种有效的方法是通过PPD的形状设计来提升大像素性能。首先全面概述了产生PPD横向电场的两种机制:边缘电场设计和钳位电压调制,并探讨了基于这两种设计策略的各种设计改进。然后总结了传输栅-浮空扩散(TG-FD)节点收集结构及像素整体布局优化的相关研究进展。此外,还研究了PPD的形状设计对暗电流的影响。通过全面分析PPD形状设计中采用的方法,为提升大像素设计提供了参考。