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J Horno - One of the best experts on this subject based on the ideXlab platform.
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differential capacitance of the Diffuse Double layer at electrode electrolyte interfaces considering ions as dielectric spheres part i binary electrolyte solutions
Journal of Colloid and Interface Science, 2017Co-Authors: J J Lopezgarcia, J Horno, Constantino GrosseAbstract:A full theoretical account of the differential capacitance of the Diffuse part of the electric Double layer at electrode-electrolyte solution interfaces is presented. It builds upon the standard electrokinetic model adding all the additional effects related to the finite ionic size. This includes steric interactions among ions by means of either the Bikerman or Carnahan-Starling expressions and all the permittivity related effects that arise when ions are represented as dielectric spheres. These include the solution permittivity dependence on the local ionic concentration, calculated by means of the Maxwell mixture formula, and two additional forces acting on the ions, namely the Born and the dielectrophoretic forces that depend on the permittivity and the electric field gradients, respectively. The obtained results show that the Diffuse Double layer behavior is sufficient to qualitatively account for the observed differential capacitance dependence on the electrode voltage. Moreover, when combined with an inner layer capacitance and using the Carnahan-Starling expression, a remarkably good quantitative agreement is achieved.
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stationary electrodiffusion adsorption processes in membranes including Diffuse Double layer effects
Journal of Membrane Science, 2001Co-Authors: A.a. Moya, J HornoAbstract:Abstract Ion transport across membranes with surface charge due to ion adsorption, including the Diffuse Double layer effects, is analysed using the network simulation method. The membrane system under study is a multilayer one constituted by a membrane and two diffusion boundary layers on both sides of the membrane. The ion transport processes are described by the Nernst–Planck and Poisson equations not only in the membrane–solution interfaces, but also in the membrane bulk and in the two diffusion boundary layers. The membrane has a negative surface charge due to an anion adsorption process. The structure of the equilibrium Diffuse Double layers and the steady-state current–voltage characteristic have been analysed for the case of an adsorption process described by a Langmuir-type adsorption isotherm. The evolution of the electric potential difference across the membrane system in the equilibrium state of the system as a function of the bathing concentrations, have been also analysed.
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application of the network simulation method to ionic transport in ion exchange membranes including Diffuse Double layer effects
Journal of Physical Chemistry B, 1999Co-Authors: A Moya A And, J HornoAbstract:The electrical properties of ion-exchange membranes have been investigated using the network simulation method. A network model is proposed for the Nernst−Planck and Poisson equations describing the ionic transport through an ion-exchange membrane and the two diffusion boundary layers on both sides of the membrane. An electric circuit simulation program is used to solve the network model in order to obtain the steady-state, transient, and small-amplitude ac electrical properties of a cation-exchange membrane in contact with an asymmetric electrolyte solution. The steady-state, chronopotentiometric, chronoamperometric, and small-amplitude ac responses of the whole membrane system have been simulated. The study is mainly intended to analyze the characteristics of the equilibrium and nonequilibrium Diffuse Double layers in ion-exchange membranes and to quantify some interesting aspects of the nonstationary polarization phenomena occurring at the charged membrane|solution interfaces.
Ronald W Fawcett - One of the best experts on this subject based on the ideXlab platform.
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properties of the Diffuse Double layer at high electrolyte concentrations
Journal of Physical Chemistry B, 2009Co-Authors: Ronald W Fawcett, Peter J Ryan, Thomas G SmagalaAbstract:The equations necessary to calculate the potential drop across the Diffuse layer and its differential capacity are derived for 1:1 electrolytes on the basis of the Eigen and Wicke theory for concentrated electrolyte solutions. The results of this model are then compared with Monte Carlo data for more concentrated solutions and solutions with ions of large diameters. It is shown that the Eigen-Wicke model is inadequate because it fails to consider the change in potential at a given ion due to its surrounding atmosphere.
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monte carlo studies of ion size effects in the Diffuse Double layer
Electrochimica Acta, 2009Co-Authors: Ronald W FawcettAbstract:Results from Monte Carlo (MC) simulations for restricted electrolytes are presented for both 1:1 and 2:1 electrolytes. It is shown that the potential drop across the Diffuse layer for these systems may be expressed by a Taylors series in the Gouy-Chapman (GC) estimate of the same quantity. The coefficients of this series are defined in terms of the MSA volume fraction and the reciprocal thickness of the ionic atmosphere. The series model can also be used to estimate the differential capacity of the Diffuse layer. The properties of unrestricted electrolytes are considered at or very close to the potential of zero charge.
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the Diffuse Double layer in ionic liquids
Collection of Czechoslovak Chemical Communications, 2009Co-Authors: Ronald W Fawcett, Peter J RyanAbstract:The equations used to describe the Diffuse Double layer in the Eigen-Wicke model of ionic liquids are presented. They are then used to estimate the potential drop across the Diffuse layer and its differential capacity for two representative systems which contain monovalent ions of equal diameter. The first one is molten RbCl at 750 °C. The second system is a room temperature ionic liquid with typical parameters to describe its properties. The results of the calculations are compared with the available experimental data. It is concluded that the Eigen-Wicke model does not consider the change in local potential experienced by a given ion in the ionic liquid. The need for Monte Carlo data for the Diffuse Double layer in molten salt systems is emphasized.
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a novel differential equation approach to modeling ion size effects in the Diffuse Double layer
Journal of Electroanalytical Chemistry, 2006Co-Authors: Thomas G Smagala, Ronald W FawcettAbstract:Abstract A new differential equation for the Diffuse Double layer is derived from the integral form of the hypernetted chain approximation (HNCA). Using the mean-spherical approximation for ion–ion interactions in the bulk, the resulting theory is found to be in excellent agreement with results obtained by the traditional solution of the HNCA integral equation for 1:1 electrolytes, provided the product of the Debye–Huckel reciprocal length and the ionic diameter is less than 1.5. The new theory is much easier to implement than the traditional method, and provides a rapid route to the estimates of the ion–wall correlation functions, Diffuse layer potential profiles, differential capacities, and ionic surface excesses for a restricted electrolyte in a primitive solvent.
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new developments in the theory of the Diffuse Double layer
Langmuir, 2006Co-Authors: Ronald W Fawcett, Thomas G SmagalaAbstract:The role of ion size effects in determining Diffuse layer properties is considered. Monte Carlo data relevant to this question are reviewed. Then the integral equation approach to the problem is considered with an emphasis on attempts to derive an analytical equation for the potential drop across the Diffuse layer. An empirical model for ion size effects is described that allows one to estimate not only the Diffuse layer potential drop but also the Diffuse layer capacity, the ionic surface excesses, and the potential distribution in the Diffuse layer. It is demonstrated that the resulting model can easily be applied by experimentalists to the analysis of experimental data for Double layer phenomena in electrochemistry and colloid science.
Richard G. Compton - One of the best experts on this subject based on the ideXlab platform.
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influence of the Diffuse Double layer on steady state voltammetry
Journal of Electroanalytical Chemistry, 2011Co-Authors: Edmund J F Dickinson, Richard G. ComptonAbstract:Abstract The influence of the Diffuse Double layer on the passage of Faradaic current is investigated for steady-state voltammetry. Both mathematical analysis and numerical solution with the Nernst–Planck–Poisson equations are employed. We report a comprehensive study of the effects of reactant charge, electrode charge, electrode size and quantity of supporting electrolyte. Both infinite and finite electrode kinetics are investigated, as well as distance-dependent electron transfer (tunnelling) and activity effects. Certain combinations of reactant and electrode charge are shown to profoundly alter the predicted current by exclusion of the reactant (Levich effect) or deceleration of apparent kinetics (Frumkin effect), although tunnelling can overcome both effects by moving the plane of electron transfer. The structurally altered Double layer at nanoelectrodes is shown to either increase or decrease the predicted current depending on the electrode charge, due to an unscreened electric field.
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how well does simple rc circuit analysis describe Diffuse Double layer capacitance at smooth micro and nanoelectrodes
Journal of Electroanalytical Chemistry, 2011Co-Authors: Edmund J F Dickinson, Richard G. ComptonAbstract:Abstract The capacitive charging of a Diffuse Double layer is discussed. Results from simple RC circuit analysis (an ideal resistor and capacitor in series) are compared with results from a more complete model in which the Nernst–Planck–Poisson equations are solved in a hemispherical space, both analytically and by simulation. This complementary approach allows an assessment of certain conditions which are required in order for RC circuit analysis to be suitable to describe the Diffuse Double layer. In particular, deviations are noted for nanoscale electrodes. Additionally, RC circuit behaviour breaks down for applied overpotentials greater than 25 mV (RT/F), such that values for solution resistance and Double layer capacitance inferred from impedance spectroscopy may not apply to other experimental techniques. These conclusions apply to a smooth electrode and so are not associated with “constant phase angle” effects.
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on the estimation of the Diffuse Double layer of carbon nanotubes using classical theory curvature effects on the gouy chapman limit
Chemical Physics Letters, 2010Co-Authors: Martin C Henstridge, Edmund J F Dickinson, Richard G. ComptonAbstract:The Poisson-Boltzmann equation is solved numerically in cylindrical space to examine the effects of curvature upon the properties of the Diffuse Double layer at a charged nanotube in electrolytic solution. Simulations reveal increased Double layer capacitance, especially for cylinders with radius less than 20 nm. The potential drop from the nanotube surface to the maximum tunnelling distance is therefore expected to be greater than for larger cylinders, providing a possibly enhanced electrochemical driving force for electron transfer and a possible partial cause for altered electrode kinetics at carbon nanotube modified electrodes. This effect is also predicted for cylinders of radius larger than 20 nm in solutions of low supporting electrolyte concentration. However, the effects on the observed electrode kinetics are predicted to be small.
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Diffuse Double layer at nanoelectrodes
Journal of Physical Chemistry C, 2009Co-Authors: Edmund J F Dickinson, Richard G. ComptonAbstract:Numerical solution of the equilibrium Poisson−Boltzmann equation for hemispherical electrodes of vanishing size reveals that the effects of curvature on the Diffuse Double layer become significant for electrodes with radii less than 50 nm. These effects include dramatically enhanced capacitance and hence more a rapid potential drop from the outer Helmholtz plane as far as the characteristic tunnelling length for electron transfer. An enhanced driving force is therefore expected for nanoelectrodes as compared to electrodes larger than 50−100 nm, especially at low concentrations of supporting electrolyte.
Snehasis Tripathy - One of the best experts on this subject based on the ideXlab platform.
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swelling pressure of a divalent rich bentonite Diffuse Double layer theory revisited
Water Resources Research, 2009Co-Authors: Tom Schanz, Snehasis TripathyAbstract:[1] Physicochemical forces are responsible for the swelling pressure development in saturated bentonites. In this paper, the swelling pressures of several compacted bentonite specimens for a range of dry density of 1.10–1.73 Mg/m3 were measured experimentally. The clay used was a divalent-rich Ca-Mg-bentonite with 12% exchangeable Na+ ions. The theoretical swelling pressure–dry density relationship for the bentonite was determined from the Gouy-Chapman Diffuse Double-layer theory. A comparison of experimental and theoretical results showed that the experimental swelling pressures are either smaller or greater than their theoretical counterparts within different dry density ranges. It is shown that for dry density of the clay less than about 1.55 Mg/m3, a possible dissociation of ions from the surface of the clay platelets contributed to the Diffuse Double-layer repulsion. At higher dry densities, the adsorptive forces due to surface and ion hydration dominated the swelling pressures of the clay. A comparison of the modified Diffuse Double-layer theory equations proposed in the literature to determine the swelling pressures of compacted bentonites and the experimental results for the clay in this study showed that the agreement between the calculated and experimental swelling pressure results is very good for dry densities less than 1.55 Mg/m3, whereas at higher dry densities the use of the equations was found to be limited.
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swelling pressure of a divalent rich bentonite Diffuse Double layer theory revisited
Water Resources Research, 2009Co-Authors: Tom Schanz, Snehasis TripathyAbstract:specimens for a range of dry density of 1.10–1.73 Mg/m 3 were measured experimentally. The clay used was a divalent-rich Ca-Mg-bentonite with 12% exchangeable Na + ions. The theoretical swelling pressure–dry density relationship for the bentonite was determined from the Gouy-Chapman Diffuse Double-layer theory. A comparison of experimental and theoretical results showed that the experimental swelling pressures are either smaller or greater than their theoretical counterparts within different dry density ranges. It is shown that for dry density of the clay less than about 1.55 Mg/m 3 ,a possible dissociation of ions from the surface of the clay platelets contributed to the Diffuse Double-layer repulsion. At higher dry densities, the adsorptive forces due to surface and ion hydration dominated the swelling pressures of the clay. A comparison of the modified Diffuse Double-layer theory equations proposed in the literature to determine the swelling pressures of compacted bentonites and the experimental results for the clay in this study showed that the agreement between the calculated and experimental swelling pressure results is very good for dry densities less than 1.55 Mg/m 3 , whereas at higher dry densities the use of the equations was found to be limited.
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swelling pressures of compacted bentonites from Diffuse Double layer theory
Canadian Geotechnical Journal, 2004Co-Authors: Snehasis Tripathy, Arunkumar Sridharan, Tom SchanzAbstract:The swelling pressures of several compacted bentonites (MX80, Febex, and Montigel) proposed for use as barrier materials in storing high-level radioactive waste in many countries were determined from the GouyChapman Diffuse Double layer theory. The swelling pressures thus determined were compared with the reported experimental swelling pressures. The study revealed that, in general, at low compaction dry densities of the bentonites, the experimental swelling pressures are less than their theoretical counterparts, with the reverse trend at high compaction dry densities. Based on the reported experimental results for the three bentonites, relationships between the nondimensional midplane potential function, u, and the nondimensional distance function, Kd, were established. New equations for the swelling pressure were proposed on the basis of the Diffuse Double layer theory and the reported experimental data to compute swelling pressures of compacted bentonites. The suitability of the new equations was also...
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swelling pressures of compacted bentonites from Diffuse Double layer theory
Canadian Geotechnical Journal, 2004Co-Authors: Snehasis Tripathy, Arunkumar Sridharan, Tom SchanzAbstract:The swelling pressures of several compacted bentonites (MX80, Febex, and Montigel) proposed for use as barrier materials in storing high-level radioactive waste in many countries were determined fr...
A.a. Moya - One of the best experts on this subject based on the ideXlab platform.
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theory of the formation of the electric Double layer at the ion exchange membrane solution interface
Physical Chemistry Chemical Physics, 2015Co-Authors: A.a. MoyaAbstract:This work aims to extend the study of the formation of the electric Double layer at the interface defined by a solution and an ion-exchange membrane on the basis of the Nernst–Planck and Poisson equations, including different values of the counter-ion diffusion coefficient and the dielectric constant in the solution and membrane phases. The network simulation method is used to obtain the time evolution of the electric potential, the displacement electric vector, the electric charge density and the ionic concentrations at the interface between a binary electrolyte solution and a cation-exchange membrane with total co-ion exclusion. The numerical results for the temporal evolution of the interfacial electric potential and the surface electric charge are compared with analytical solutions derived in the limit of the shortest times by considering the Poisson equation for a simple cationic diffusion process. The steady-state results are justified from the Gouy–Chapman theory for the Diffuse Double layer in the limits of similar and high bathing ionic concentrations with respect to the fixed-charge concentration inside the membrane. Interesting new physical insights arise from the interpretation of the process of the formation of the electric Double layer at the ion exchange membrane–solution interface on the basis of a membrane model with total co-ion exclusion.
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stationary electrodiffusion adsorption processes in membranes including Diffuse Double layer effects
Journal of Membrane Science, 2001Co-Authors: A.a. Moya, J HornoAbstract:Abstract Ion transport across membranes with surface charge due to ion adsorption, including the Diffuse Double layer effects, is analysed using the network simulation method. The membrane system under study is a multilayer one constituted by a membrane and two diffusion boundary layers on both sides of the membrane. The ion transport processes are described by the Nernst–Planck and Poisson equations not only in the membrane–solution interfaces, but also in the membrane bulk and in the two diffusion boundary layers. The membrane has a negative surface charge due to an anion adsorption process. The structure of the equilibrium Diffuse Double layers and the steady-state current–voltage characteristic have been analysed for the case of an adsorption process described by a Langmuir-type adsorption isotherm. The evolution of the electric potential difference across the membrane system in the equilibrium state of the system as a function of the bathing concentrations, have been also analysed.