Time-Fractional Phase Field Model of Electrochemical Impedance

In this paper, electrochemical impedance responses of subdiffusive phase transition materials are calculated and analyzed for one-dimensional cell with reflecting and absorbing boundary conditions. The description is based on the generalization of the diffusive Warburg impedance within the fractional phase field approach utilizing the time-fractional Cahn–Hilliard equation. The driving force in the model is the chemical potential of ions, that is described in terms of the phase field allowing us to avoid additional calculation of the activity coefficient. The derived impedance spectra are applied to describe the response of supercapacitors with polyaniline/carbon nanotube electrodes.

AC conductivity of superionic thallium sulfide crystals exposed to γ-irradiation

The frequency dependence of the thallium sulfide (TlS) crystal impedance is analyzed in wide frequency and temperature range for the hopping and superionic conduction mechanisms. It has been established that in weak alternating electric fields, there is a hopping mechanism of charge transfer. The use of impedance spectroscopy methods in TlS crystals, at temperatures of 300, 350 and 400 K in the frequency range of 2*106 Hz and subjected to [Formula: see text]-irradiation doses 0, 0.25 and 0.75 MGy charge transfer processes, has been investigated. Hodographs constructed from the data of experimental measurements of 400 K, in the low-frequency region ([Formula: see text] Hz) and regardless of the absorbed gamma quanta, indicating additional contributions to the conductivity, presumably corresponds to the fact that in the frequency range of the applied signal, carrier diffusion does not reach the diffuse layer. This type of hodographs at low frequencies is characteristic of the Warburg impedance.

Effects of water and sodium dodecyl sulfate additives on Cr(III) ions electroreduction in a deep eutectic solvent

Kinetics of Cr(III) ions electroreduction in a deep eutectic solvent (ethaline) was studied by using electrochemical impedance spectroscopy. The influence of water and sodium dodecyl sulfate on the kinetic parameters was established. The developed equivalent circuit included polarization resistance of the electrochemical reaction, constant phase element and finite Warburg impedance. The respective parameters of the accepted equivalent circuit were calculated and discussed. The obtained results indicated that the charge transfer is a rate-determining step of an electrochemical reaction occurring on a heterogeneous electrode surface. An increase in content of water in electrolytes resulted in an increase in polarization resistance, indicating the deceleration of Cr(III) ions electroreduction due to the changes in Cr(III) speciation. In addition, the introduction of extra water caused an increase in the value of a capacitive component of electrochemical impedance because of a rearrangement of the double electrical layer. The polarization resistance of Cr(III) ion discharge was increased in the presence of sodium dodecylsulfate in electrolyte due to adsorption of dodecylsulfate anion on the electrode surface. A Warburg impedance component disappeared in electrolytes containing relatively high water content, which was associated with corresponding reduction of solution viscosity and acceleration of diffusion mass transfer.

Preparation and Electrochemical Properties of Flow-Through TiO2 Nanoarray

Microstructure-tailored TiO2 nanoarrays with adjustive wall-hole morphology have been designed to improve electrochemical properties. Tubular, porous and flow-through TiO2 nanoarrays are fabricated by one-stepped, two-stepped and three-stepped anodization process under the controlled reaction condition. Tubular nanoarray with the opened-mouth and closed-bottom has a tube diameter of 120-130nm, a length of 8.12μm, and wall thickness of 15nm. Similarly, porous TiO2 nanoarray with the opened-mouth and closed-bottom has a pore diameter of 60-70nm, a length of 8.25μm, neighboring wall distance of 70-80nm. Comparatively, flow-through TiO2 nanoarray with the opened-mouth and opened-bottom has a pore diameter of 110-120nm, a length of 8.56μm, neighboring wall distance of 40nm. In comparison with tubular and porous TiO2 nanoarrays, flow-through TiO2 nanoarray indicates the deceased charge transfer resistance and diffusion-related Warburg impedance, presenting the enhanced current response at the same electrode potential. Accordingly, bottom-opened flow-through TiO2 nanoarray achieves the specific capacitance of 6.35 mF cm-2, which is higher than the bottom-closed tubular and porous TiO2 nanoarrays (2.94 and 3.78 mF cm-2). The flow-through TiO2 nanoarray presents the improved electrochemical performance for the electrochemical energy-storage.

Impedance of copper electrode in slightly acid Cu(II)-glycine solutions

Electrochemical impedance spectroscopy was used to study the kinetics of reduction of Cu (II) in weakly acidic (pH 4 and 5) solutions of Cu (II) containing glycine (0.04 or 0.1 M) as a complexing agent. A rather slow equilibration was observed at pH 4 and glycine concentration cL = 0.04 M. With increasing pH or cL, the total concentration of intermediate Cu(I) decreases. At the same time, impedance increases over the entire range of frequencies applied. An equivalent circuit with two parallel sub-circuits, each containing the charge transfer resistance and Warburg impedance in series, was used to quantify the impedance spectra. The exchange current densities of two consecutive one-electron transfers were estimated. Their average values are ~1 µA cm–2 and ~0.1 mA cm–2.

Application of 1,2,3-Benzotriazole as Corrosion Inhibitor for Mild Steel in Sulphuric Acid Medium at Different Temperature

Corrosion inhibition property of 1,2,3-benzotriazole for mild steel in 0.1 N sulphuric acid was evaluated at different concentrations and temperatures using weight loss, electrochemical polarization, differential pulse, stripping voltammetry and impedance spectroscopy. The surface study was carried out using metallurgical research and SEM microscopy. Increase in Warburg impedance and capacitive current and decrease in Faradaic current and capacitive loop was observed with increase in concentration of inhibitor. 1,2,3-Benzotriazole was found as a best corrosion inhibitor (94 %) for mild steel as compared to other inhibitors suggesting 1,2,3-benzotriazole as a potential alternate corrosion inhibitor for mild steel in H2SO4.