Electrochemical Impedance Spectroscopy

Commercially available bulk niobium diselenide (NbSe 2) reduced into nanomaterials upon exfoliation typically contains oxide and carbide impurities. Liquid-phase exfoliated two-dimensional (2D) nanosheets of NbSe 2 obtained from bulk powders provide high charge mobility and large surface area but become self-passivated and chemically inert as the presence of oxide impurities makes them behave more semimetallic. In this article, we report the effects of inherent impurities of liquid-phase exfoliated 2D NbSe 2 (intended to be integrated as supercapacitor electrodes) on the electrochemical performance. The highest specific capacitances achieved using 1-butyl-3-methylimidazolium hexafluorophosphate (BMIMPF 6) and sulfuric acid (1 M H 2 SO 4) electrolytes were 4955.5 ± 21.5 and 13 361.6 ± 31.8% mF/cm 2 , respectively, which were affected by the impurities, oxophilicity of niobium defects, and moisture adsorption in the cell. Galvanostatic charge−discharge profiles show moisture adsorption affecting the high-energy charging procedure in the cell for BMIMPF 6 , resulting in leakage and decomposition of the electrolyte. Electrochemical impedance spectroscopy provides insights into the solid-electrolyte interphase and charge-transfer mechanisms at exfoliated 2D NbSe 2 nanosheets, which affect the ion intercalation through heterogenous phases of the nanosheets. Overall, the NbSe 2 nanosheets offer heterogenous phases because of the coexistence of Nb 2 O 5 that influences the charge-transfer mechanism at the exfoliated surfaces.

This study describes the use of electrodeposited nanostructured hybrid nickel–cobalt hexacyanoferrate in electrochemical supercapacitors. Herein, various compositions of nickel and cobalt hexacyanoferrates (Ni/CoHCNFe) nanostructures are electrodeposited on an inexpensive stainless steel substrate using cyclic voltammetric (CV) method. The morphology of the electrodeposited nanostructures is studied using scanning electron microscopy, while their electrochemical characterizations are investigated using CV, galvanostatic charge and discharge and electrochemical impedance spectroscopy. The results show that the nanostructures of hybrid metal cyanoferrate, shows a much higher capacitance (765 F g−1) than those obtained with just nickel hexacyanoferrate (379 F g−1) or cobalt hexacyanoferrate (277 F g−1). Electrochemical impedance spectroscopy results confirm the favorable capacitive behavior of the electrodeposited materials. The columbic efficiency is approximately 95% based on the charge and discharge experiments. Long cycle-life and excellent stability of the nanostructured materials are also demonstrated during 1000 cycles.► Nanostructured hybrid nickel–cobalt hexacyanoferrate is used in supercapacitors. ► A high capacitance (765 F g−1) is obtained at a specific current of 0.2 A g−1. ► Long cycle-life and excellent stability are demonstrated during 1000 cycles.

The implementation of concrete and its association with a release agent influence the aesthetics of the concrete facings. The mineral oils tend to be replaced by vegetable formulations, to reduce the impact of the substances spilled in the environment. From a technical point of view, it is important to characterize the action of these new formulations at the interface concrete/oil/formwork. Two performing techniques have been used to study the physico-chemical processes, the tribometry and electrochemical impedance spectroscopy. The correlation of the results obtained allowed to improve the understanding of the mechanisms involved at the interface mould/oil, in connection with the use of an acidifier in the formulation. La mise en œuvre du béton et son association avec un agent de démoulage, influence l’esthétique des parements en béton. Les huiles minérales tendent à être remplacées par des formulations à base végétale, afin de réduire l’impact des substances rejetées dans l’environnement. Sur un plan technique, il est important de caractériser le mode d’action de ces nouvelles formulations, à l’interface béton/huile/coffrage. Les travaux s’appuient notamment sur l’utilisation de deux techniques performantes pour étudier les phénomènes physico-chimiques, la tribométrie et la spectroscopie d’impédance électrochimique. La corrélation entre les résultats obtenus permet d’améliorer la compréhension des mécanismes impliqués à l’interface de démoulage, en relation avec l’utilisation d’un acidifiant dans la formulation.

The electrochemical behavior of Cu–Ni alloys with different Ni contents (5–65mass%) in acidic sulfate solutions was investigated. The effects of working conditions e.g. concentration of sulfate ions, immersion time and temperature were studied and discussed. In this respect, open-circuit potential measurements, polarization techniques and electrochemical impedance spectroscopy (EIS) were used. Potentiodynamic measurements revealed that the increase in the Ni content

Based on permittivity changes, a new method to measure hematocrit (HCT) in extracorporeal blood systems is presented. Human blood samples were tested at different HCT levels pairing the values of permittivity change, obtained by means of a commercial impedance analyzer, with traditional centrifugation measurements. Data were correlated using both linear and nonlinear regression. When using the lineal model, the comparison

A modified synthesis process was developed based on co-precipitation method followed by spray drying process. In this process, a spherical shaped (Co 1/3 Ni 1/3 Mn 1/3 )(OH) 2 precursor was synthesized by co-precipitation and pre-heated at 500 °C to form a high structural stability ...

In this study SiO 2 -like films have been deposited by Plasma Enhanced Chemical Vapour Deposition (PECVD) on Mg alloys employed in the automotive industry in different experimental conditions in order to optimize the protective effectiveness of the deposited layers. The experimental apparatus used was a capacitive coupled (CC) parallel-plate-reactor with an asymmetric electrode configuration, the electromagnetic radiation was applied

There is considerable interest in using interdigitated arrays as sensors in both aqueous and non-aqueous fluids. However, highly resistive non-aqueous fluids present substantially different design constraints than conductive aqueous and polar non-aqueous solutions. Analytical equations for the performance of planar interdigitated devices in highly resistive non-aqueous industrial fluids were developed and used to design a series of prototypes. Theoretical expressions describing the cell constant, bulk and interfacial resistances and capacitances of interdigitated sensors are reported, leading to conclusions on appropriate empirical and modeling evaluation methods for design and optimization of interdigitated sensors for testing in highly resistive solutions. Electrochemical impedance spectroscopy (EIS) was used to compare prototype performance to analytical equations. In addition, the prototype devices were compared to solid parallel plate electrodes, which are typically used for EI...

A conductivity relaxation experiment has been conducted on an SrFeCo0.5Ox sample by abruptly changing the oxygen partial pressure in the atmosphere and monitoring the change of conductivity as a function of time. The re-equilibrium process obeys Fick's second law. By fitting the relaxation data to the solution of the diffusion equation with appropriate boundary conditions, we could determine the oxygen chemical diffusion coefficient and the activation energy. The oxygen diffusion coefficient is 8.9 × 10−7 cm2/s at 900 °C and it increases with increase in temperature. Measured activation energy is 0.92 eV, which is slightly lower than that of other oxides in the system SrFe1 − xCoxOy.