Leonid Daikhin

Influence of surface roughness on the quartz crystal microbalance response in a solution New configuration for QCM studies

The effect of surface roughness on a quartz crystal microbalance (QCM) response in contact with a liquid has been investigated. A perturbation theory was used for the description of the effect of slight roughness and an approach based on Brinkmans equation was used for strongly rough surfaces. In the latter approach, one treats the flow of a liquid through a non-uniform surface layer as the flow of a liquid through a porous medium. Our description includes both the effect of viscous dissipation in the interfacial layer and the effect of the liquid mass rigidly coupled to the surface. A relation between QCM response and the interface geometry has been found. We suggested a new approach to study the QCM response in liquids that provides an effective way to analyse the effect of roughness. The models discussed here can be used for the treatment of QCM response of rough electrode surfaces, of porous deposited films, and of surface polymer films.

Nonlinear Poisson–Boltzmann theory of a double layer at a rough metal/electrolyte interface: A new look at the capacitance data on solid electrodes

Nonlinear Poisson–Boltzmann theory is developed to extend our previous work [Phys. Rev. E 53, 6192 (1996)] on the case when the potential drop across the double layer is not small compared to the thermal energy. Close to the potentials of zero charge (pzc) the effect of surface roughness on the double-layer capacitance is mainly determined by an interplay between the lateral correlation length of roughness and the Debye length. However, far from the pzc dramatic effects of electrode potential are found which are not reduced to the potential-induced shortening of the diffuse layer thickness.

Slippage at adsorbate–electrolyte interface. Response of electrochemical quartz crystal microbalance to adsorption

Abstract The electrochemical quartz crystal microbalance (EQCM) was used to study adsorption of pyridine on gold from aqueous and butanol solutions. It was found that the effect of specific adsorption on the frequency shift could not be explained in terms of a mass change in the adsorbed layer that rigidly coupled to the oscillating surface. In order to explain our observations we suggest a model, which accounts for two important features of adsorption at solid–electrolyte interfaces: (a) an adsorbate replaces a certain amount of solvent molecules from the interfacial layer, and (b) adsorption may lead to a finite slippage at the adsorbed layer–solution interface. Relationships between the slip length and the microscopic properties of the interfacial layer are discussed, and a dependence of the slip length on surface excesses is suggested. The treatment of experimental data makes it possible to determine the slip length as a function of surface excesses, for pyridine adsorption on gold from aqueous and butanol solutions.

In situ hydrodynamic spectroscopy for structure characterization of porous energy storage electrodes

A primary atomic-scale effect accompanying Li-ion insertion into rechargeable battery electrodes is a significant intercalation-induced change of the unit cell volume of the crystalline material. This generates a variety of secondary multiscale dimensional changes and causes a deterioration in the energy storage performance stability. Although traditional in situ height-sensing techniques (atomic force microscopy or electrochemical dilatometry) are able to sense electrode thickness changes at a nanometre scale, they are much less informative concerning intercalation-induced changes of the porous electrode structure at a mesoscopic scale. Based on a electrochemical quartz-crystal microbalance with dissipation monitoring on multiple overtone orders, herein we introduce an in situ hydrodynamic spectroscopic method for porous electrode structure characterization. This new method will enable future developments and applications in the fields of battery and supercapacitor research, especially for diagnostics of viscoelastic properties of binders for composite electrodes and probing the micromechanical stability of their internal electrode porous structure and interfaces.

Surface morphology and the quartz crystal microbalance response in liquids

Abstract The effect, of surface roughness and the morphology of non-uniform surface films, on a quartz crystal microbalance (QCM) response in contact with a liquid has been investigated. We used a perturbation theory for the description of the effect of slight roughness and an approach based on Brinkmans equation for the case of strong roughness. In the latter approach one treats the flow of a liquid through a nonuniform surface layer as the flow of a liquid through a porous medium. Our description includes both the effect of viscous dissipation in the interfacial layer and the effect of the liquid mass rigidly coupled to the surface. A relation between QCM response and the interface geometry has been found. The models discussed here can be used for the treatment of the QCM response of rough electrode surfaces, of porous deposited films and of surface polymer films.

Capillary waves at soft electrified interfaces

Recent theory of capillary waves along the interface between two immiscible electrolytes is generalized to include the non-linear polarization of the double layer. The theory covers both the effects of the capillary waves on the double layer capacitance, as well as the effect of charging the interface on the amplitudes and spectrum of capillary waves. The theory explains major available experimental data, such as the interfacial capacitance dependence on the potential drop across the interface and on ionic strength. It also predicts a number of new effects, such as the influence of electric field and electrolyte concentration on the surface corrugation correlation function, and in particular, on the mean square height of corrugation.

Ion penetration into an ‘unfriendly medium’ and the double layer capacitance of the interface between two immiscible electrolytes

We develop a theory of the double layer at electrolyte | electrolyte interfaces with account for the finite thickness of the interfacial region. This includes the distribution of ions between the two phases and smooth variation of dielectric properties across the interface. The theory offers simple laws for the dependence of the double layer capacitance on the nature of ions, ionic concentrations and potential, which are in line with experimental observations. The theory shows which parameters reflect the nature of ions and the structure of the interface, and how these parameters can be extracted from the capacitance data.

Response of the EQCM for electrostatic and specific adsorption on gold and silver electrodes

The response of the electrochemical quartz crystal microbalance (EQCM) has been studied on gold and silver electrodes in solution, with and without specifically adsorbed species. The frequency shifts with potential, even in the absence of specific adsorption. The shift is comparable to that caused by specific adsorption. The frequency shift caused by adsorption of pyridine depends strongly on the nature of the metal. By three independent series of experiments: without specific adsorption, with adsorption of pyridine and with silver deposition on gold, it was shown that the interaction of a gold surface with water is much stronger than that of silver.

Non‐Invasive In Situ Dynamic Monitoring of Elastic Properties of Composite Battery Electrodes by EQCM‐D

Reversible Li-ion intercalation into composite Li-ion battery (LIB) electrodes is often accompanied by significant dimensional electrode changes (deformation) resulting in significant deterioration of the cycling performance. Viscoelastic properties of polymeric binders affected by intercalation-induced deformation of composite LIB electrodes have never been probed in situ on operating electrochemical cells. Here, we introduce a newly developed noninvasive method, namely electrochemical quartz-crystal microbalance with dissipation monitoring (EQCM-D), for in situ monitoring of elastic properties of polymeric binders during charging of LIB electrodes. As such, we find EQCM-D as a uniquely suitable tool to track the binders structural rigidity/softness in composite Li insertion electrodes in real-time by the characteristic increase/decrease of the dissipation factor during the charging-discharging process. The binders partially swollen in aprotic solutions demonstrate intermediate viscoelastic charge-rate-dependent behavior, revealing rigid/soft behavior at high/low charging rates, respectively. The method can be adjusted for continuous monitoring of elastic properties of the polymeric binders over the entire LIB electrodes cycling life.

Admittance studies of the EQCM on rough surfaces. The double layer region

Abstract The admittance of the electrochemical quartz crystal microbalance (EQCM) was studied for gold surfaces of different morphologies, produced by electrodeposition of gold at current densities near the limiting current density. It was observed that at surfaces of certain morphology, the real and the imaginary parts of the EQCM response become very sensitive to changes of potential in the double-layer region, even when Faradaic reactions and specific adsorption do not take place. This effect masks smaller effects of mass and viscosity changes in the diffuse double layer, described in our previous publication. It was suggested that this rather large effect is a result of surface hydration, depending on electrode potential. Orientation of water molecules in the first layer attached to the surface results in a shift of the equilibrium between clusters of water of different sizes in the “transition” layer. The latter determines the viscosity of this layer.