电流型葡萄糖传感器阴极的研究

本文研究了石墨、银、钛基RuO2 /TiO2 涂层材料等几种导电材料取代铂作为葡萄糖传感器阴极的可能性 .结果表明 ,钛基RuO2 /TiO2 涂层电极的化学性质稳定 ,对析氢反应有一定的催化作用 .由石墨_环氧胶粘剂混合物—钛基RuO2 /TiO2 组成的电化学体系可以在 0 .6～ 0 .8V电压范围内检测H2 O2 的稳态氧化电流 ;在 0 .7V电压下 ,以钛基RuO2 /TiO2 涂层材料作为阴极的葡萄糖传感器的性能与以铂片为阴极的传感器性能接近 ,钛基RuO2 /TiO2 涂层材料是取代铂的最佳阴极材料 .     

Modeling of the trajectories of the hydrogen bubbles evolving from the cathode in a fluorine production cell

The fluid velocity and temperature fields and the trajectories of the hydrogen bubbles evolving from the cathode in a fluorine production cell were studied by using the finite element method. It was examined the effect of the configuration of the slits formed on the cathode on the escape of the hydrogen bubbles toward the backside of the cathode to reduce the ohmic voltage loss between the electrodes. The results showed that the cathode configuration has a profound effect on both of the flow pattern near the cathode and the bubble trajectories. It was found that the cathode with the slits only on the upper half of the electrode is more effective in removing the bubbles to the backside of the cathode than the one with the slits over the entire electrode.     

固态氧化物阴极过程的离子扩散模型及其Ta2O5熔盐电解验证

固态氧化物阴极在氯化钙熔盐电解质中的脱氧速率可依据氧离子的稳态扩散模型（PRS模型）由固态氧化物阴极孔隙率P,还原后金属与还原前氧化物之间的摩尔体积比R,还原后阴极的体积收缩率S等参数直接计算. PRS模型重要意义还在于可提供极简单的公式以预测不同金属氧化物还原时固态阴极的优化孔隙率,而固态阴极孔隙率对其脱氧速率有显著影响. 对于Ta₂O₅电解,其固态阴极孔隙率不易大于50%. 相关理论预测结果得到了固态Ta₂O₅在氯化钙熔盐中电解实验的良好验证,表明PRS模型对固态化合物阴极的快速、高效电解具有重要的指导意义.     

Modeling the effect of the cathode geometry in a DC glow discharge ion source for mass spectrometry

A self-consistent, two-dimensional hybrid fluid-particle model is used to study the effect of cathode geometry on the plasma produced in an argon glow discharge for conditions typically of the commercially available glow discharge mass spectrometer system (VG9000 spectrometer and Megacell source). For a given power supply voltage and gas pressure, we show that the spatial distribution of the plasma in the discharge volume is strongly dependent on the cathode geometry. The plasma created in a discharge with a pin cathode tends to form a ring around the cathode, while the plasma in a discharge with a larger diameter, disk cathode is centered on-axis between the cathode face and the anode. The ion current arriving at the entry plane of the mass spectrometer thus depends strongly on the cathode geometry. This suggests that analytical performance can be enhanced by optimization of the cathode (sample) geometry.     

Characterization of the arc cathode attachment by emission spectroscopy and comparison to theoretical predictions

Emission spectroscopic diagnostics of electron temperature distribution and electron number density distribution in the cathode region have been carried out employing an OMA/spectrometer system. Single color and two color pyrometry of cathode temperature distributions have also been performed. The experimental results are compared with results of a theoretical model formulated previously to study the arc cathode interaction.The results show that the plasma in the cathode region strongly deviates from LTE. Thermionic cooling is the major cooling mechanism of cathodes at high arc currents. The work function of 2% thoriated tungsten cathodes increases during arcing due to fast evaporation of thorium from 2% thoriated tungsten cathodes.     

A Sheath Collision Model with Thermionic Electron Emission and the Schottky Correction Factor for Work Function of Wall Material

This paper is a further development of the collisional sheath model at the thermionic cathode for two temperature modeling of thermal arcs that was recently suggested by Pekker and Hussary. In the present work, the Schottky correction factor to the work function of the electrode material is calculated taking into account the friction of ions in the sheath, while in the model of Pekker and Hussary it was calculated neglecting this friction. The model is applied to the cathode spot at the tungsten cathode in argon. It is demonstrated that a virtual cathode can be formed in the atmospheric pressure argon plasma at the cathode surface if the cathode current density is sufficiently small. The heat flux to the thermionic cathode due to charged particles and the heat flux to the plasma due to thermionic electrons are calculated. The obtained results are compared with the model of Pekker and Hussary. The sheath potential drop and the heat fluxes calculated by this model can be used as boundary conditions at the wall for the electric potential and for the energy equations for the electrons and heavy particles (ions and neutrals) in two temperature modeling of thermal plasma.     

A critical review of spectral and related physical properties of the hollow cathode discharge

Investigations made over the last fifty years, of the electrical properties which differentiate a hollow cathode d.c. discharge from one before a plane cathode, have been summarized. The wide range of dimensions and pressure conditions used by different workers have been considered, and related where possible to results, to give a more unified picture. Data are collected on energies and densities of electrons, and of positive ions, in hollow cathode cavities, with a view to establishing the principles governing spectral line emission. Results of measurements on spectral line intensities, of carrier gases and of atoms sputtered from the cathode, are discussed in relation to the activity, already considered, of electrons and positive ions. The gaps and contradictions in present knowledge of conditions for useful light emission are indicated.     

富锂正极材料的衰减机理及循环稳定性提升的研究进展

富锂正极材料xLi2MnO3·(1-x)LiMO2(M=Ni,Co,Mn等,0＜x＜1)具有容量高(可达300 mA·h/g以上)、成本低的巨大优势,被誉为是可能的最为重要的下一代锂离子电池正极材料,受到了各国的高度重视和广泛研究.目前,这种材料尚存在初始(首圈)库仑效率低、循环性能差、电压衰减严重等问题,严重阻碍了材...     

The influence of cathode flow field surface properties on the local and time-dependent performance of direct methanol fuel cells

The influence of cathode flow field wettability on the local and time-dependent performance of DMFCs was investigated by galvanostatic measurements of local current distribution, cell voltage and pressure drop along the cathode channels. The cathode flow fields made of graphite were either untreated, hydrophobic or hydrophilic. Drop shape analysis yielded contact angles in the descending order hydrophobic (126.8°), untreated (115.9°) and hydrophilic (26.2°). Especially at low air stoichiometry (λ_air = 2), hydrophilic cathode flow fields are advantageous with regard to higher power densities, suppression of local current fluctuations and substantial reduction of pressure drop along the cathode channels.     

富锂正极材料结构设计和表面调控的研究进展

富锂正极材料因具有较高的理论能量密度,被视为极具发展潜能的新一代正极材料,但该材料在循环过程中容量和电压衰减显著,导致其实际商业应用受阻.本文综合评述了通过结构设计和表面调控提高富锂正极材料储锂性能的研究进展,介绍了富锂正极材料的充放电工作机制,及导致其比容量和电压衰减的原因,讨论了近年来通过新型结构设计(如构筑蛋黄-蛋壳中空结构、中空多壳层结构等)和表面调控(如尺寸控制、暴露晶面控制、表面尖晶石化、表面包覆、表面掺杂等）策略,抑制富锂正极材料表面氧析出和晶型转变并稳定材料结构,从而抑制电压和比容量衰减,有效提高电池的循环寿命和库伦效率的相关研究成果,最后,提出了通过结构设计和表面调控提高富锂正极材料电化学性能面临的挑战,并对未来发展方向进行了展望.     

Operating mechanism of the electrolyte cathode atmospheric glow discharge

Cathode fall ( U(cf)), cathodic current density and atomic emission intensities originating from metal salts in the electrolyte cathode were measured as a function of different discharge parameters. Emission intensities in function of cathode fall indicate a potential barrier in the sputtered mass flux. This means that the primary particles of the cathode sputtering are of positive charge and the cathode fall including its internal variables is the most important factor. The measured current density and the U(cf) as a function of pressure are in accordance with the low pressure data in the literature. The observed decrease of the U(cf) with decreasing pH was explained by a model in that the secondary electron emission coefficient of the cathode (gamma) is controlled through a reaction net of competing reactions of different electron scavengers involving the hydroxonium ions of the cathode solution. The model revealed two different electron emission processes of the electrolyte cathode, an emission coupled with hydrated electrons is dominating below pH 2.5 while a proton-independent emission of poor efficiency is working above pH 3. Our model fits to the reported yields of the ultimate products both in the solution and in the gas phase and offers a calculation of gamma and U(cf) in the function of the cathode acidity. The model provides two other independent gamma calculation methods based on product analysis data.     

Influences of synthesis route and preparation process on the electrochemical properties of Fe-doped strontium cobaltite

SrCo_0.8Fe_0.2O_3-δ (SCF), as a promising cathode material for intermediate temperature solid oxide fuel cells, possesses a high catalytic activity for the reduction of O₂ to 2O²⁻. The SCF powder was successfully synthesized by the solid state reaction method and Pechini method and characterized using XRD, particle analysis, and electrochemical performance measurements. Smaller-particle-size SCF materials (SCF-P) with single phase are obtained at lower synthesis temperature by the Pechini method and possess better electrochemical performance as compared with those prepared by the solid state reaction method. The reason is that the Pechini method involves the mixing of elements at atomic level, so pure SCF phase formation can be accelerated and showed high electrocatalytic activity. The preparation procedure of SCF cathode was firstly investigated using electrochemical impedance spectroscopy. Results show that the total polarization resistance and the low-frequency resistance decrease gradually with the reduction of the calcination temperature for the SCF cathodes. The SCF-P cathode sintered at 1,000 °C possesses the highest porosity and the best electrochemical performance. It is the result of a comprehensive function of three-phase boundary length, porosity of cathode, and the adhesion between cathode and electrolyte. The charge-transfer process, together with the adsorption, dissociation, and diffusion of oxygen, has a strong influence on the whole reaction process of the cathode. The influence of binder amounts on the performance of the SCF-P cathodes was also studied.     

Effect of sodium dodecyl sulfate on the rate of hydrogen evolution at a cathode

The effect of H(2) evolution on the mass-transfer coefficient of cathode reduction of potassium ferricyanide at a mercury cathode was studied with the aim of (i) comparing the mass transfer behavior at a Hg cathode with that at solid electrodes under gas-evolving conditions and (ii) testing the effect of anionic surface-active agent on the mass transfer behavior of an H(2)-evolving Hg cathode. It is found that the mass transfer coefficient at the Hg cathode was much higher than the value at a solid cathode. The mass transfer coefficient at H(2)-evolving Hg was found to decrease in the presence of sodium dodecyl sulfate (SDS) surfactant by an amount ranging from 58.8 to 76%, depending on the H(2) discharge rate and the SDS concentrations.     

Zr4+离子掺杂对LiFePO4结构及电化学性能的影响

应用固相反应法于惰性气氛下合成掺Zr的L iFePO4正极材料.考察Zr4+掺杂浓度对于目标化合物结构及其电化学性能的影响.XRD,交流阻抗和恒流充放电测试等实验表明,少量的Zr4+掺杂并未影响目标材料产物的结构,反而有利于降低L iFePO4电荷转移反应的阻抗,从而有利于克服该电极过程中的动力学限制.该正极材料表现出优良的倍率放电性能,在0.1C倍率下,L i0.99Zr0.01FePO4的首次放电比容量达135.6mAh.g-1.30次循环后,容量衰减仅3.8%.     

Active layer of the oxygen cathode in a fuel cell with Nafion and platinum: The role played by the diffusion and ohmic restrictions and the selection of the working thickness of the active layer

The basic parameters that characterize the operation of the active layer of a cathode with Nafion are the effective coefficient of the diffusion of oxygen, the effective ionic conductance, and the thickness of the active layer. One of the deficiencies intrinsic to the fuel cells containing Nafion is their extreme sensitivity to the heat and moisture exchange. Nafion demands an optimum degree of humidification. Upon thoroughly draining the active layer of a cathode with Nafion, its effective ionic conductance substantially lowers, and large diffusion restrictions arise following the flooding of pores in the active layer. The goal of this work is to perform a comparison of values of some dimensional characteristics pertaining to the flooded and thoroughly drained active layers of a cathode with similar indicators of an active layer in its optimum (normal) state. It is demonstrated how one should perform the selection of the working thickness of an active layer that would provide for the efficiency of its functioning.     

In-situ Raman Studies on the Oxide Species of Cathode in MCFC

In MCFC the mechanism of cathode reaction is more complex than that of anode reaction. It is very important to clarify the reaction mechanism of cathode in order to direct the selection of cathode materials. The oxide species present in molten carbonate is the key to understand the mechanism of cathode reaction. Although there have been many papers to discuss the oxide species formed at cathode, no general conclusions have been reached so far, some results even contradicted. Appleby and Nicholson stated that peroxide ion appears to be the predominant species in the Li/K eutectic, but some other researchers concluded that the dominant species is superoxide ion in this melt.     

Electrosynthesis of cyclopropanes at the electrolysis of solutions of methyl esters of Di- and trichloroacetatic acids in aprotic media in the presence of acrylonitrile

The potentiostatic (galvanostatic) electrolysis of methyl esters of trichloroacetic acid on mercury (steel) cathodes in the cathodic compartment of a diaphragm cell in the presence of acrylonitrile affords a mixture of two stereoisomers of methyl ester of 1-chloro-2-cyanocyclopropanecarboxylic acid. The process involves a stage of dehalogenation of the original methyl ester followed by the reaction of the formed anion with acrylonitrile and proceeds more efficiently on a mercury cathode in the dimethylformamide medium with the current efficiency of 94% and the substance yield of 25%. In contrast to methyl trichloroacetate, the electrolysis of methyl dichloroacetate proceeds by an indirect mechanism involving its deprotonation on the steel cathode and by the cleavage of the C-Cl bond on the mercury cathode. In both cases, the acrylonitrile addition leads to formation of the corresponding cyclopropane structures. Moreover, the process is the most efficient on the steel cathode in the MeCN medium. In the latter case, the current efficiency of methyl ester of 1-chloro-2-cyanocyclopropanecarboxylic acid is 31% and substance yield is 41%. Peculiarities of these processes are discussed.     

LiNi_(0.8-y)Ti_yCo_(0.2)O_2电极材料中钛离子掺杂作用机理的研究

应用恒流充放电、非现场X射线粉末衍射 (ex situXRD)、电化学交流阻抗 (EIS)、程序控温脱附 质谱联用(TPD MS)等实验方法研究LiNi0. 8-yTiyCo0. 2O2电极材料钛离子的掺杂作用机理.结果表明,掺钛后的电极材料于充放电过程中的结构相变和晶格的膨胀收缩受到抑制,在高电位下的界面反应活性减弱,从而减小了由结构变化和界面反应引起的容量损失;同时,钛的掺杂增强了电极材料在脱锂状态下的结构稳定性,抑制了电极材料和电解液的分解或氧化反应,以上两个方面分别改善并提高了电极材料的充放电循环性能及其热稳定性.     

Breakdowns and the formation of microdischarge channels in surface barrier discharges

The dynamics of the space-time evolution of a creeping (surface) barrier discharge in pure oxygen at atmospheric pressure was studied by numerical simulation. The breakdown through a gas gap was found to end by the formation of a cathode layer. The distribution of parameters in this layer was close to that in the “normal” cathode layer. The cathode layer, which was a source of electrons, sustained the formation of a microdischarge channel above a dielectric. Microdischarge channel elongation over a dielectric was shown to be effected by a streamer formed in the head of the channel and to be accompanied by charge fall-out onto the surface of the dielectric barrier. This noticeably decreased the mean electric field strength in the channel and the intensity of discharge processes and eventually caused their cessation.     

Formation and Role of a Hollow-Cathode Plasma Plug in Mass-Spectrometric Analysis

The use of plasma electron and ion sources based on a glow discharge is often restricted by a too high plasma-forming gas pressure in the process volume. Experiments with a new design of a hollow cathode, a type of glow discharge, are described in this paper. It was found that, if a cap with an orifice is arranged at the vertex of a cylindrical hollow cathode (the orifice diameter is 10 to 90% of the inner diameter of the hollow cathode), a plasma plug, which offers resistance to a plasma-forming gas flow from the cathode hole to the vacuum chamber, is formed in the cathode hole near the orifice. As a result, a pressure drop is formed between the cathode hole and the vacuum chamber. This pressure drop depends on the orifice diameter, and it can be as high as three orders of magnitude with the use of a hollow cathode with an internal diameter of 20 mm and an orifice diameter of 4 mm in the cap at the cathode vertex.