Diffusivity and conductivity of a primitive model electrolyte in a nanopore

Equilibrium and non-equilibrium molecular dynamics simulations are applied to obtain the diffusion coefficient and electric conductivity of ions in dilute electrolytes confined in neutral cylindrical pores. The electrolyte is described with the restricted primitive model and the wall of the pore is modelled as a soft wall. The equilibrium molecular dynamics simulations show that the axial diffusion coefficient of ions decreases with increasing confinement. For a fixed pore radius the diffusion coefficient decreases with increasing number density of the ions. The current response of the system to an applied electric field is maintained at constant temperature by Gaussian isokinetic equations of motion, and at constant concentration by periodic boundary conditions with recycling of ions in the axial direction. The electric conductivity is calculated from the current density and the electric field applied for different pore sizes. In contrast to the trend in diffusivity, conductivity increases slightly in smaller pores. For a very small pore, however, conductivity is lower than the bulk, because oppositely charged ions moving in opposite directions under the electric field cannot avoid collisions with each other in a narrow channel.     

Nonlinear ion transport in liquid and solid electrolytes

This paper describes nonlinear ion transport properties of liquid and solid electrolytes. Typically, the relation between ionic current density and electric field becomes nonlinear at electric fields above 50–100?kV/cm. We review the 1st and 2nd Wien effect found in classical strong and weak electrolyte solutions as well as the strong nonlinear ion transport effects observed for inorganic glasses and for polymer electrolytes. Furthermore, we give an overview over models describing nonlinear ion transport in electrolyte solutions, in glasses and in polymers. Recent results are presented for the nonlinear ionic conductivity of supercooled ionic liquids. We show that supercooled ionic liquids exhibit anomalous Wien effects, which are clearly distinct from the classical Wien effects. We also discuss the frequency dependence of higher-order conductivity and permittivity spectra of these liquids.     

Structure of a planar electric double layer containing size-asymmetric ions: density functional approach

We have studied the structure of the electrolytes with asymmetries in charge and size near a charged planar electric double layer by a density functional theory. In the present theory, the hard-sphere contribution has been approximated as the direct pair correlation function with the coupling parameter, whereas the electronic contribution has been approximated as the mean-spherical approximation in the bulk phase. This theoretical approach for the size-symmetric and size-asymmetric electrolytes displays a good agreement with the simulation results over a wide range of surface charge densities and electrolyte concentrations. However, the accuracy between the present theory and the simulation results slightly deteriorates for the highly size-asymmetric electrolytes and the multivalent electrolytes. In these cases, the performance of the present theory is comparable to those of the simplified extension of the Poisson–Boltzmann theory and the modified Poisson–Boltzmann theory. The calculated result indicates that the surface charge distribution function, which was introduced as an indicator for studying the charge reversal, layering effect, and surface charge amplification in a planar electric double layer, describes the electronic properties of a planar electric double layer well.     

The electric conductivity of stationary and homogeneous electrolytes up to concentrations c ≈ 1 mol/l and high electric fields

Following a previous paper the electric conductivity of stationary and homogeneous electrolytes at high electric fields is investigated. It turns out that the increase of the molar conductivity at high electric fields which is observed experimentally can be explained only if an additional boundary condition in the differential equation for the pair distribution is taken into account. As a consequence also the electric conductivity at low electric fields is modified. The numerical results for hydrous electrolytes are in a good agreement with experimental data.     

Electrohydromechanical analysis based on conductivity gradient in microchannel

Fluid manipulation is very important in any lab-on-a-chip system. This paper analyses phenomena which use the alternating current （AC） electric field to deflect and manipulate coflowing streams of two different electrolytes （with conductivity gradient） within a microfluidic channel. The basic theory of the electrohydrodynamics and simulation of the analytical model are used to explain the phenomena. The velocity induced for different voltages and conductivity gradient are computed. The results show that when the AC electrical signal is applied on the electrodes, the fluid with higher conductivity occupies a larger region of the channel and the interface of the two fluids is deflected. It will provide some basic reference for people who want to do more study in the control of different fluids with conductivity gradient in a microfluidic channel.     

High-voltage conductivity of α-RbAg4I5, α-KAg4I5, and α-KCu4I5 superionic conductors

It is found that the conductivity of RbAg₄I₅, KAg₄I₅, and KCu₄I₅ solid electrolytes in the ??-phase rises with the electric field strength and tends to a limit value in fields on the order of 1 MV/m. The high-voltage limit of conductivity exceeds the low-voltage one by 100% or more. The application of an intense electric pulse raises the conductivity of the electrolytes by 35%, and the activated state exhibits an anomalously long relaxation time.     

表面镀金SU-8微柱的低频电动旋转特征

依据传统Maxwell-Wagner界面极化理论, 金属微纳米粒子由于具有极高电导率, 在旋转电场作用下无明显电旋转运动. 然而, 本文针对镀金SU-8微柱开展实验研究, 发现镀金微柱在低频条件下的快速旋转运动现象. 据此, 通过考虑镀金微柱表面双电层效应, 理论分析并实验验证镀金微柱的低频电旋转特征. 首先, 建立电场中微柱的近似椭球模型, 分析固-液接触面双电层作用下的金属粒子极化机理, 推导旋转电场作用下镀金微柱的转矩公式及电旋转角速度公式. 其次, 搭建实验平台, 分别对镀金微柱在三种不同电导率溶液、100 Hz–30 MHz频率范围内的电旋转特征进行对比实验研究. 最后, 对实验结果进行分析和讨论, 并通过考虑镀金微柱与基底之间摩擦作用等因素, 验证实验研究与理论研究的一致性. 关键词： 表面镀金微柱 电旋转 双电层 微流控     

Enhancement of the electrochemical properties with the effect of alkali metal systems on PEO/PVdF-HFP complex polymer electrolytes

Polymer blend electrolytes based on poly(ethylene oxide) (PEO) and poly(vinylidene fluoride-hexafluoropropylene) (PVdF-HFP) were prepared by using different lithium salts LiX (X = ClO₄, BF₄, CF₃SO₃, and N [CF₃SO₂]₂) using solution casting technique. To confirm the structure and complexation of the electrolyte films, the prepared electrolytes were subjected to X-ray diffraction (XRD) and Fourier transform infrared spectroscopy (FTIR) analysis. Alternating current (AC) impedance analysis was performed for all the electrolyte samples at various temperatures from 303 to 343 K. The result suggests that among the various lithium salts, LiN[CF₃SO₂]₂-based electrolytes exhibited the highest ionic conductivity at 8.20 × 10^?4 S/cm. The linear variation of the ionic conductivity of the polymer electrolytes with increasing temperature suggests the Arrhenius-type thermally activated process. Activation energies were found to decrease when doping with lithium imide salt. The dielectric behavior has been analyzed using dielectric permittivity (ε*), electric modulus (M*), and dissipation factor (tanδ) of the samples. Cyclic voltammetry has been performed for the electrolyte films to study their cyclability and reversibility. Thermogravimetric and differential thermal analysis (TG/DTA) was used to ascertain the thermal stability of the electrolytes, and the porous nature of the electrolytes was identified using scanning electron microscopy via ion hopping conduction. Surface morphology of the sample having maximum conductivity was studied by an atomic force microscope (AFM).     

Nonequilibrium mechanisms of weak electrolyte electrification under the action of constant voltage

The formation of space charge in weak electrolytes, specifically in liquid dielectrics, has been considered. An analytical solution is given to a simplified set of Nernst–Planck equations that describe the formation of nonequilibrium recombination layers in weak electrolytes. This approximate analytical solution is compared with computer simulation data for a complete set of Poisson–Nernst–Planck equations. It has been shown that the current passage in weak electrolytes can be described by a single dimensionless parameter that equals the length of a near-electrode recombination layer divided by the width of the interelectrode gap. The formation mechanism and the structure of charged nonequilibrium near-electrode layers in the nonstationary regime have been analyzed for different injection-to-conduction current ratios. It has been found that almost all charge structures encountered in weak dielectrics can be accounted for by the nonequilibrium dissociation–recombination mechanism of space charge formation.     

Aqueous electrolytes’ transport through nanopores of polymeric membrane

Ion permeation and the selectivity of sodium and potassium ions through the nanopores of polyethylene terephthalate (PET) have been investigated at room temperature using the conductometric technique. The nanopores in PET with the high aspect ratio have been created using the ion track technology. The passive (due to the concentration gradient) and active transport (due to the applied potential) of aqueous electrolytes (i.e.; NaClO₄ and KClO₄ and their different combinations) has been studied. Along with the effect of concentration and electric field gradient, the effect of anion accumulation outside the nanopores on the transport of electrolytes has also been analysed using time series and current–voltage measurements. The transportation and selection of ions also depends on the hydration energy of the ions. A detailed study of transport of ions through the nanopores explains their I–V and I–t behaviour due to the inter- and intra- molecular interaction and their effective interaction with the walls of the nanopores.     

含水量对TiO_2纳米管形貌控制参数的影响

以不同含水量的乙二醇溶液为电解液,采用阳极氧化法制备TiO2纳米管阵列。通过记录反应过程中电导率、粘度及回路电流随时间的变化曲线,研究含水量对电解液粘度、电导率及电流等过程参数的影响,分析了纳米管形貌尺寸与TiO2溶蚀所耗电荷量的关系。粘度初始值和初始电导率均与含水量呈三次关系,相关系数分别为0.992 5和0.977 8。在反应过程中,溶液粘度值有缓慢增加的趋势。由于不同含水量的电解液粘度的不同,H+和OH-数量不同,F-迁移速率不同,电导率-时间曲线及电流-时间曲线具有不同的变化趋势,并对其进行了理论分析。当水体积分数为4%,5%,6%和10%时,纳米管的形貌较为有序并且TiO2纳米管阵列表面的碎片较少,纳米管直径变化范围为50nm至72nm,长度变化范围为0.85~1.90μm。F-腐蚀氧化膜时所消耗电量与TiO2氧化膜被腐蚀掉的体积呈一次函数关系,即腐蚀电量越大,腐蚀掉的体积越大,为制备一定形貌尺寸的纳米管提供了一定的控制方法。     

Using impedance to study surface segregation on restored electrodes of Ag-Sn and Au-Sn alloys

Results from investigating time dependences for the capacitance of double electric layers, observed from the time of the mechanical restoration of electrodes of Ag-Sn, Au-Sn binary alloys with low contents of the second component in solutions of surface-inactive electrolytes, are analyzed. It is shown that the observed time dependences are due to surface segregation of the second component of alloys at the boundary with a solution.     

Onsager-Manning-Oosawa condensation phenomenon and the effect of salt

Making use of results pertaining to Painlevé III type equations, we revisit the celebrated Onsager-Manning-Oosawa condensation phenomenon for charged stiff linear polymers, in the mean-field approximation with salt. We obtain analytically the associated critical line charge density and show that it is severely affected by finite salt effects, whereas previous results focused on the no salt limit. In addition, we obtain explicit expressions for the condensate thickness and the electric potential. The case of asymmetric electrolytes is also briefly addressed.     

Dielectric properties and fluctuating relaxation processes of poly(methyl methacrylate) based polymeric nanocomposite electrolytes

Solid polymer nanocomposite electrolytes (SPNEs) consisted of poly(methyl methacrylate) (PMMA) and lithium perchlorate (LiClO₄) of molar ratio C=O:Li⁺=4:1 with varying concentration of montmorillonite (MMT) clay as nanofiller have been prepared by classical solution casting and high intensity ultrasonic assisted solution casting methods. The dielectric/electrical dispersion behaviour of these electrolytes was studied by dielectric relaxation spectroscopy at ambient temperature. The dielectric loss tangent and electric modulus spectra have been analyzed for relaxation processes corresponding to the side groups rotation and the segmental motion of PMMA chain, which confirm their fluctuating behaviour with the sample preparation methods and also with change of MMT concentration. The feasibility of these relaxation fluctuations has been explained using a transient complex structural model based on Lewis acid–base interactions. The low permittivity and moderate dc ionic conductivity at ambient temperature suggest the suitability of these electrolytes in fabrication of ion conducting electrochromic devices and lithium ion batteries. The amorphous behaviour and the exfoliated/intercalated MMT structures of these nanocomposite electrolytes were confirmed by X-ray diffraction measurements.     

Decoupling of ionic transport from segmental relaxation in polymer electrolytes

We present detailed studies of the relationship between ionic conductivity and segmental relaxation in polymer electrolytes. The analysis shows that the ionic conductivity can be decoupled from segmental dynamics and the strength of the decoupling correlates with the fragility but not with the glass transition temperature. These results call for a revision of the current picture of ionic transport in polymer electrolytes. We relate the observed decoupling phenomenon to frustration in packing of rigid polymers, where the loose local structure is also responsible for the increase in their fragility.     

Thermal transport in lithium-ion battery: A micro perspective for thermal management

In recent years, lithium ion (Li-ion) batteries have served as significant power sources in portable electronic devices and electric vehicles because of their high energy density and rate capability. There are growing concerns towards the safety of Li-ion batteries, in which thermal conductivities of anodes, cathodes, electrolytes and separator play key roles for determining the thermal energy transport in Li-ion battery. In this review, we summarize the state-of-the-art studies on the thermal conductivities of commonly used anodes, cathodes, electrolytes and separator in Li-ion batteries, including both theoretical and experimental reports. First, the thermal conductivities of anodes and cathodes are discussed, and the effects of delithiation degree and temperature of materials are also discussed. Then, we review the thermal conductivities of commonly used electrolytes, especially on solid electrolytes. Finally, the basic concept of interfacial thermal conductance and simulation methods are presented, as well as the interfacial thermal conductance between separator and cathodes. This perspective review would provide atomic perspective knowledge to understand thermal transport in Li-ion battery, which will be beneficial to the thermal management and temperature control in electrochemical energy storage devices.     

Soft chemical route and new solid oxide fuel cells

Solid oxide fuel cells (SOFCs) are a promising technology for electric power generation in the 21st century. Recently, research are focusing on reduced temperature SOFCs. The fabrication of thin film electrolytes and electrode membranes for reduced temperatures by a soft chemical route is discussed. Paper presented at the 97th Xiangshan Science Conference on New Solid State Fuel Cells, Xiangshan, Beijing, China, June 14–17, 1998.     

The effect of uni/bipolar charge injection on EHD conduction pumping

Electrohydrodynamics (EHD) conduction pumping takes advantage of Coulomb force generated by externally applied electric field and dissociated charges from electrolytes present in the working fluid. With the electric field maintained below the DC breakdown limit (i.e voltage required for charge injection), EHD conduction generated flow relies primarily upon the asymmetry of the electrodes where the flow is always generated toward the specific direction regardless of the electrodes polarity. The charge distribution induced by the process of dissociation may be altered by charge injection, potentially present at the electrodes' surfaces. The charge injection could occur, for example, because of the electrode surface roughness.This paper is a numerical investigation to quantify the impact of the charge injection on the performance of EHD conduction pump. The numerical domain comprises a coplanar asymmetric electrode pair embedded against a 2-D channel wall where the EHD conduction induced liquid flow is expected to be generated from the narrower electrode toward the wider electrode in the absence of charge injection. The electric field, net charge density, and electric body force distributions are presented in the absence and presence of charge injection. In addition, the electrically generated net flow is calculated for several operating conditions.     

一种新型的染料敏化紫外光电池

利用浸渍提拉法制备了纳米TiO₂多孔膜.采用紫外光源,以[Fe(CN)₆]^3-/[Fe(CN)₆]^4-溶液为电解质,分别以两种染料敏化纳米TiO₂膜为光阳极制成了一种新型的紫外光电池,探讨了该电池的伏安特性曲线.电池最大电压为0.36 mV,最大电流密度为0.02 μA/cm²,同时对染料敏化电极的光电转换机理进行了初步讨论.     

Structural, vibrational and electrical characterization of PVA-NH4Br polymer electrolyte system

Polymer electrolyte based on PVA doped with different concentrations of NH₄Br has been prepared by solution casting technique. The complexation of the prepared polymer electrolytes has been studied using X-ray diffraction (XRD) and Fourier transform infra red (FTIR) spectroscopy. The maximum ionic conductivity (5.7×10⁻⁴ S cm⁻¹) has been obtained for 25 mol% NH₄Br-doped PVA polymer electrolyte. The temperature dependence of ionic conductivity of the prepared polymer electrolytes obeys Arrhenius law. The ionic transference number of mobile ions has been estimated by dc polarization method and the results reveal that the conducting species are predominantly ions. The dielectric behavior of the polymer electrolytes has been analyzed using dielectric permittivity and electric modulus spectra.