Influence Of Electrical Double Layer Research Articles

Nature of the electric double layer to modulate the electrochemical behaviors of Fe2O3 electrode

The electric double layer (EDL) has been found to play a critical role in not only electric double-layer capacitors (EDLCs) but also batteries and electrocatalysts. Although the influence of EDLs on the electrochemical behaviors of electrolytes has been extensively investigated, its influence on the electrode itself, particularly the energy storage mechanism, remains unclear. Herein, using popular α-Fe2O3, we look into the interaction between electrode and EDL and find the energy storage mechanism of an electrode can be tuned by modulating EDL. The EDL, which is mainly influenced by the inner Helmholtz plane (IHP) through the specific adsorption of ions onto the surface of Fe2O3, determines which ions are present at the interface and how they react with the electrode. Ultimately, the composition and properties of the EDL determine the energy storage mechanism of an Fe2O3 electrode, including conversion reaction, ions insertion, surface redox reaction and pseudocapacitance. Our results not only provide a new understanding on the nature of the EDL but also demonstrate that the EDL should be promoted as a functional "component" which can be designed for achieving the optimum synergy of an electrode-electrolyte interface.

Integrating electric double layer time-varying and dual interface slip for predicting migration behavior of moisture and ions

Migration of moisture and chloride ions in calcium-silicate-hydrates (C-S-H) nanopores is important factor for controlling the durability of concrete and affecting the physical and chemical properties of cement-based binder. Quantitative analysis of experimental results indicates that the pore in C-S-H is mainly distributed on the nanometer scale. Due to the prominent interfacial effects at the nanoscale, moisture and ions in different regions within nanochannels exhibit distinct molecular structures and dynamic properties. Therefore, the wetting behavior of the synthesized C-S-H surface and its influence on microfluid dynamics analysis and boundary condition definition were systematically analyzed based on the contact angle experiment. Statistical thermodynamics were introduced to describe the time-varying characteristics of the electric double layer (EDL). With the interaction as the theoretical framework and interaction energy as an important parameter, the equilibrium behavior of interacting particles was studied to describe the stability of EDL system. The flow control equation and boundary conditions were modified considering the action of EDL. The transport model of moisture and chloride ions under the combined influence of electric double layer and dual interface slip was proposed. The results show that the existence of EDL impedes the movement of the fluid, while the dual slippage of water film and time-varying of EDL reduce the resistance. Quantitative analysis indicates the contribution ratios of water film slip and EDL time-varying can reach 85% and 29%, respectively. In addition, water film slip has a greater influence on water migration and EDL time-varying has a greater influence on ions. This research can provide new insights into the transport mechanism of water and chloride ions at micro-nanoscale.

Dynamic Transport Control of Colloidal Particles by Repeatable Active Switching of Solute Gradients.

Diffusiophoresis (DP) is described as typically being divided into chemiphoresis (CP) and electrophoresis (EP), and the related theory is well-established. However, not only the individual effect of CP and EP but also the size dependency on the resulting DP of colloidal particles has not yet been comprehensively demonstrated in an experimental manner. In this paper, we present a dynamic transport control mechanism for colloidal particles by developing a micro-/nanofluidic DP platform (MNDP). We demonstrate that the MNDP can generate transient and/or steady-state concentration gradients, making it possible to control the direction and rate of transport of colloidal particles through the individual manipulation of CP and EP by simply and rapidly switching solutions. In addition, the MNDP allows the size-dependent separation as well as fractionation of submicron particles through the individual manipulation of CP and EP, thus empirically validating the classic theoretical model for DP under the influence of electrical double layer (EDL) thickness. Furthermore, we provide theoretical analysis and simulation results that will enable the development of a versatile separation and/or fractionation technique for various colloidal particles, including biosamples, according to their size or electrical feature.

Pore‐scale modelling of complex conductivity of saturated granular materials

ABSTRACTThe complex conductivity method has been frequently used in solving hydrogeological, engineering, and environmental problems in practice. Macroscopic geophysical responses are governed by pore‐scale rock properties; therefore, a clear petrophysical understanding of how the pore‐scale structure controls electric conduction and polarization in geomaterials is necessary to fully interpret laboratory‐/field‐scale geophysical observations. In this study, we have developed a pore‐scale numerical approach to calculate the complex conductivity of water‐saturated granular materials. This physics‐based model has advantage over phenomenological or empirical models such that the intrinsic relations between pore structure and geoelectrical signals could be revealed. In the modelling, the influence of electrical double layer, which is quantified by complex surface conductance, can be converted to an apparent volumetric complex conductivity of either solid particles or pore fluid. The effective complex conductivity of the sample is determined by directly solving the finite‐difference representation of the Laplace equation in the domain of a representative elementary volume. The numerical approach is tested on one synthetic sample and one glass beads sample. For the synthetic sample, the consistency between the numerical and the analytical solution confirms the accuracy of the approach. Comparison with experimental measurements of the glass beads sample reported previously indicates that the developed numerical approach can well reproduce the key characteristics of the complex conductivity of water‐saturated granular materials in the frequency range between 10‐1 and 104 Hz. Furthermore, the numerical examples also show that the proposed approach can capture the salinity‐dependent electric conduction and polarization in saturated granular materials.

Theory for electrochemical impedance spectroscopy of heterogeneous electrode with distributed capacitance and charge transfer resistance

Abstract Randles-Ershler admittance model is extensively used in the modeling of batteries, fuel cells, sensors etc. It is also used in understanding response of the fundamental systems with coupled processes like charge transfer, diffusion, electric double layer charging and uncompensated solution resistance. We generalize phenomenological theory for the Randles-Ershler admittance at the electrode with double layer capacitance and charge transfer heterogeneity, viz., non-uniform double layer capacitance and charge transfer resistance (\(c_d\) and \(R_{CT}\)). Electrode heterogeneity is modeled through distribution functions of \(R_{CT}\) and \(c_d\), viz., log-normal distribution function. High frequency region captures influence of electric double layer while intermediate frequency region captures influence from the charge transfer resistance of heterogeneous electrode. A heterogeneous electrode with mean charge transfer resistance \(\overline{R_{CT}}\) shows faster charge transfer kinetics over a electrode with uniform charge transfer resistance (\(\overline{R_{CT}}\)). It is also observed that a heterogeneous electrode having high mean with large variance in the \(R_{CT}\) and \(c_d\) can behave same as an electrode having low mean with small variance in the \(R_{CT}\) and \(c_d\). The origin of coupling of uncompensated solution resistance (between working and reference electrode) with the charge transfer kinetics is explained. Finally, our model provides a simple route to understand the effect of spatial heterogeneity.Graphical Abstract SYNOPSIS An electrochemical system consisting of heterogeneous working electrode (non-uniform charge transfer (CT) resistance (\(R_{CT}^{(i)}\)) and electric double layer capacitance (\(c_{d}^{(i)}\))) and ohmic losses (\(R_\Omega \)) between working and reference electrode. The analysis suggests that electrode with heterogeneity results in faster CT kinetics as compared to CT kinetics over homogeneous electrode.

Electromechanical instability of nanobridge in ionic liquid electrolyte media: influence of electrical double layer, dispersion forces and size effect

In this paper, the electromechanical response and instability of the nanobridge immersed in ionic electrolyte media is investigated. The electrochemical force field is determined using double-layer theory and linearized Poisson–Boltzmann equation. The presence of dispersion forces, i.e., Casimir and van der Waals attractions are incorporated considering the correction due to the presence of liquid media between the interacting surfaces (three-layer model). The strain gradient elasticity is employed to model the size-dependent structural behavior of the nanobridge. To solve the nonlinear constitutive equation of the system, three approaches, e.g., the Rayleigh–Ritz method, Lumped parameter model and the numerical solution method are employed. Impacts of the dispersion forces and size effect on the instability characteristics as well as the effects of ion concentration and potential ratio are discussed.

Influence of Electrical Double Layer in the Electrical Model for Capacitance- based Soil Moisture Sensor on Measuring Soil Moisture

The reasonable electrical model for Capacitance-Based Soil Moisture Sensor (CBSMS), namely relationship between soil moisture and sensor output voltage, is the basic requirement of soil moisture measurements. In the present study, two CBSMS (PA-1 for the self-developed CBSMS and EC-5 for decagon company’s CBSMS) were employed to assess influence of electrical double layer in the electrical model for CBSMS on measuring soil moisture based on 15 soil samples with moisture ranging from 2.6~30%. Results showed that significant deviations of experimental results and estimated values were determined mainly in dependence on the electrical models (Model-1: with electrical double layer, Model-2: without electrical double layer), soil moisture range and sensor itself. Significant deviations were observed in the moisture range of 2.6~6%, 22~30% for EC-5 and of 2.6~10%, 22~30% for PA-1 with Model-2, whereas the deviations did not exist for both CBSMS in the moisture range of 2.6~10% with Model-1. For both CBSMS, in the moisture range of 22~30%, the deviation between estimated values from Model-1 with experimental results was obviously less than that from Model-2. These results suggest that the electrical double layer should be considered in the electrical model for CBSMS, especially for measuring low soil moisture.

Analytical consideration of thermodynamic jump condition

At a gas-liquid interface, there are many unknown physical and chemical phenomena related to thermodynamics, electromagnetics, hydrodynamics, and heat and mass transfer. Therefore, a modeling of gas-liquid interface is one of key issues of interfacial phenomena of multiphase flows. In the previous our study, having assumed that the interface is a thin membrane and has a finite thickness, we have developed a new mathematical model of the gas-liquid interface based on thermodynamics and mathematical approach. In that study, we have derived the new equation of free energy based on the lattice gas model including the influence of electric double layer on the interface caused by a contamination. Then, by using this interface model, we derive the jump condition at gas-liquid interface treated by thermodynamics. In this study, we discuss on the thermodynamic jump condition in macroscopic scale through the analytical treatment. Finally, we reveal the force vector fields on the gas-liquid interface depending on an electric potential and a distribution of the contamination at the interface.

Theoretical analysis and experimental study on the influence of electric double layer on thin film lubrication

A new mathematical model for thin film lubrication is established by taking into account the effect of an electric double layer. In the present paper, experiments are carried out on a self-made tester. With a composite block and a rotating disk, influence of electric double layer on thin film lubrication is studied. Two different methods are used to reconstruct the field of electric double layer so as to change its effect. One is to change the ionic concentration of lubricants by adding additives, and the other is to apply an external electric field on friction pairs. According theoretical analysis, both the methods will apparently change the electro-viscosity of the lubricant film so as to change the lubrication performances. After theoretical calculation of electro-viscosity is amended according to the experimental results, the equations of electro-viscosity are presented. The results show that the equivalent viscosity of fluid induced by the effect of electric double layer apparently increases with the decrease of thickness of the film while the lubrication film is thin enough. The effect of electro-viscosity is weakened as the thickness of the film increases. Moreover, the effect of electro-viscosity increases with the increase of external electric field at first. When the voltage reaches a certain value, the electro-viscosity begins to decrease.

Behaviour of porous materials impregnated with a liquid dielectric

The initial purpose of this work was to elaborate a model for an impregnated semi-crystalline polymer (such as polypropylene). The liquid dissolves out part of the amorphous phase of the polymer, and after impregnation, we can consider the impregnated material as a microporous membrane; the problem is to determine the “geometry” of the micro-pores (with electron microscope no valuable information was obtained). We decided as an approach to the problem, to work on porous media (such as sintered glass, porous PTFE, etc…) and to study • - the dielectric response (ε′, ε″) on a wide spectrum of frequency, with different liquids (2 < ε r < 70), at different level of conductivity (modified by addition of organic salts) • - the current-voltage response I (V) under DC or step voltage (and also with A.C.); to appreciate the mean mobility of carriers, the transient current was studied using either ion-exchange membranes as injectors or metallic electrodes. The influence of electrical double layer and electrokinetic phenomena (mainly electro-osmosis) is discussed. We think that this work is new in the field of porous media (subjected to high fields and impregnated with insulating liquids).