ABSTRACT
An analysis of the ionic transport properties of BMIM [NTf2] in supported ionic-liquid-like phase (SILLP)-based membranes has been carried out based on experimental impedance spectroscopy measurements. The direct current (dc)-conductivity was analyzed to determine the temperature and frequency dependence. The fit of the loss tangent curve data with the Cole-Cole approximation of the electrode polarization model provides the conductivity, diffusivity, and density of charge carriers. Among these quantities, a significant increase in conductivity is observed when an ionic liquid is added to the polymeric matrix containing imidazolium fragments. The use of a recent generalization of Eyring's absolute rate theory allowed the elucidation of how the local entropy restrictions, due to the porosity of the polymeric matrix, control the conductive process. The fit of the conductivity data as a function of temperature manifests the behavior of the excess entropy with respect to the temperature. The activation entropy and enthalpy were also determined. Our results correlate the Debye length (LD) with the experimental values of conductivity, electrode polarization relaxation time, and sample relaxation time involved. Our work provides novel insights into the description of ionic transport in membranes as the diffusivity, mobility, and free charge density depend on the LD. Moreover, we discuss the behavior of the polarization relaxation time, the sample relaxation time, and the static permittivity as a function of the temperature.
ABSTRACT
Correction for 'Temperature dependence of anomalous protonic and superprotonic transport properties in mixed salts based on CsH2PO4' by Andreu Andrio et al., Phys. Chem. Chem. Phys., 2019, 21, 12948-12960, DOI: 10.1039/C8CP07472K.
ABSTRACT
The crystallographic structure of solid electrolytes and other materials determines the protonic conductivity in devices such as fuel cells, ionic-conductors, and supercapacitors. Experiments show that a rise of the temperature in a narrow interval may lead to a sudden increase of several orders of magnitude of the conductivity of some materials, a process called a superprotonic transition. Here, we use a novel macro-transport theory for irregular domains to show that the change of entropic restrictions associated with solid-solid phase or structural transitions controls the sudden change of the ionic conductivity when the superprotonic transition takes place. Specifically, we deduce a general formula for the temperature dependence on the ionic conductivity that fits remarkably well experimental data of superprotonic transitions in doped cesium phosphates and other materials reported in the literature.
ABSTRACT
We present an experimental study and a theoretical interpretation of the temperature dependence of the transport properties of doped CsH2PO4 salts in both protonic and superprotonic phases. Cesium phosphate based solid electrolytes are technologically relevant because their operational temperature range is about 100 to 300 °C in which a superprotonic transition may manifest depending on its mixed composition. The experimental study was carried out using impedance spectroscopy at the temperature range of 150-230 °C, and the protonic and superprotonic transport properties and proton concentrations were calculated and analyzed by using the electrode polarization, and the Debye and Cole-Cole models for the dielectric constant. We have shown that the transport properties predicted by the Cole-Cole model are consistent with the conductivity measurements whereas the Debye model shows some inconsistencies. We attribute this to the fact that the Cole-Cole model incorporates the effects of interactions among charge carriers better than the more commonly used Debye model. In this way, our work shows a more consistent approach to determine the transport properties of solid electrolytes and, therefore, provides a more reliable tool to analyze the transport properties of heterogeneous solid electrolytes that can be used in electrochemical devices, including fuel cells and supercapacitors.
ABSTRACT
We study the wetting behavior on spherical walls by ternary mixtures of oil, water, and an amphiphile. We use the Ginzburg-Landau free energy with a single order parameter and find that there are different stable structures of the interface and that a quasiwetting transition is the mechanism involved in the transition among them. We calculate these wetting transitions for two sets of parameters in the bulk free energy which are known to show microemulsion behavior. The surface transitions are thin-thick first-order transitions (continuous transitions are absent), and the phase diagram in surface parameter space is constructed. For the first set of bulk parameters water, oil, and a microemulsion coexist, and we study the first-order transition where the oil phase wets the wall-microemulsion interface and its behavior as the radius of the wall becomes large. Therefore, we recover the known wetting transitions on a planar wall. In the second set of bulk parameters only water and oil coexist, and for some sizes of the solid wall, the oil phase wets the wall-water interface, and the phase behavior is extremely rich. We obtain a coexistence of four surface phases or two triple points followed by three lines of first-order transitions which end at three critical points depending on the radius of the surface. When there are micellar metastable solutions in bulk, the behavior of the thickness of the wetting layer of the oil phase as the radius of the spherical wall gets larger is nonmonotonic. We associate this behavior with the intrinsic micelle structure due to the spontaneous curvature of the model.
