Conductivity (electrolytic)

Résumé

Conductivity (or specific conductance) of an electrolyte solution is a measure of its ability to conduct electricity. The SI unit of conductivity is siemens per meter (S/m). Conductivity measurements are used routinely in many industrial and environmental applications as a fast, inexpensive and reliable way of measuring the ionic content in a solution. For example, the measurement of product conductivity is a typical way to monitor and continuously trend the performance of water purification systems. In many cases, conductivity is linked directly to the total dissolved solids (TDS). High quality deionized water has a conductivity of about 0.05 μS/cm at 25 °C, typical drinking water is in the range of 200–800 μS/cm, while sea water is about 50 mS/cm (or 0.05 S/cm). Conductivity is traditionally determined by connecting the electrolyte in a Wheatstone bridge. Dilute solutions follow Kohlrausch's Laws of concentration dependence and additivity of ionic contr

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https://en.wikipedia.org/wiki/Conductivity_(electrolytic)

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A mixed anion hydroborate/carba-hydroborate as a room temperature Na-ion solid electrolyte

Matteo Brighi, Radovan Cerny

The novel compound Na2-x(CB11H12)(x)(B12H12)(1-x) shows a fast ionic Na conductivity of 2 mS cm(-1) at room temperature, reaching the superionic regime above 333 K. A low activation energy of 314 meV, in a thermodynamically and electrochemically stable structure, suggest its usage as a potential solid electrolyte in future all solid Na-ion batteries. Density functional theory simulations indicate the heterovalent anionic mixing to be the responsible in stabilizing a bcc structure, which allows a facile Na+ diffusion already at room temperature. Cyclic voltammetry measurement with a tailored setup for solid-state electrolytes reveals a wide operating window (up to 4.1 V vs. Na+/Na). The symmetrical cell featuring Na-Sn alloy-based electrodes shows reversible Na+ shuttling with limited polarization after more than 700 operating hours.

ELSEVIER SCIENCE BV2018

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Enhanced Room-Temperature Ionic Conductivity of NaCB11H12 via High-Energy Mechanical Milling

Claudia Esther Avalos, Matteo Brighi, Radovan Cerny

The body-centered cubic (bcc) polymorph of NaCB11H12 has been stabilized at room temperature by highenergy mechanical milling. Temperature-dependent electrochemical impedance spectroscopy shows an optimum at 45-min milling time, leading to an rt conductivity of 4 mS cm(-1). Mechanical milling suppresses an order-disorder phase transition in the investigated temperature range. Nevertheless, two main regimes can be identified, with two clearly distinct activation energies. Powder X-ray diffraction and Na-23 solid-state NMR reveal two different Na+ environments, which are partially occupied, in the bcc polymorph. The increased number of available sodium sites w.r.t. ccp polymorph raises the configurational entropy of the bcc phase, contributing to a higher ionic conductivity. Mechanical treatment does not alter the oxidative stability of NaCB11H12. Electrochemical test on a symmetric cell (Na vertical bar NaCB11H12 vertical bar Na) without control of the stack pressure provides a critical current density of 0.12 mA cm(-2), able to fully charge/discharge a 120 mA h g(-1) specific capacity positive electrode at the rate of C/2.

AMER CHEMICAL SOC2021

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This thesis analyzes the properties of heavily doped nanocrystalline titanium dioxide. Thin films were deposited by magnetron sputtering with either water vapor as reactive gas or a periodically interrupted oxygen supply. The samples were at the same time electrically conducting and transparent. They consisted of mixtures of rutile, anatase and amorphous phases. Titanium dioxide is chemically stable, hard, non-toxic, transparent, and inexpensive. Due to a high refractive index it is often found in optical applications as a thin film coating. For many purposes it is interesting to take advantage of a combination of good transparency and electrical conductivity. An even larger field of applications would open if the electric conductivity of TiO2 could be increased in a controlled manner. Conventional bulk doping is limited, however, by low solubility limits. Highly conducting nanocrystalline TiO2 thin films have been obtained recently by sputtering in presence of water vapor. The present project intends to elucidate the doping mechanisms at work in such films. In addition, an alternative process to achieve grain-boundary doping of TiO2 was explored. Spectrophotometry over a wide spectral range (0.05 to 5 eV) was the main tool in probing the mobile electrical charge carriers. The interpretation of these optical measurements required appropriate models. The models developed took many structural properties into account, such as thickness, surface roughness, density, anisotropy and crystalline phase composition. The phase and morphology of the films were analyzed by X-ray diffraction and reflection, scanning probe microscopy, and electron microscopy. The chemical analyses included electron-probe microanalyses, Rutherford backscattering and elastic recoil detection analysis. The DC electrical properties were measured between room temperature and 250 °C. Most water-deposited samples showed semiconducting behavior with an activation energy of the order of 100 meV. The optical measurements revealed a broad absorption band around 1 eV. The absorption coefficient scaled with conductivity. It was successfully modelled as a Lorentzian. Similar absorption bands have been reported for reduced rutile and anatase single crystals. Water-deposited samples containing anatase exhibited a metallic behavior. In these samples the thermal activation energy was reduced to about 30 meV and the charge carriers displayed a high mobility (3 cm2V-1s-1). The infrared absorption band was about 10 times less important than in the samples devoid of anatase. Thin films of TiO2 intercalated with the equivalent of nanometer-thick layers of Ti were prepared. By changing the period in the oxygen supply the grain size, and thereby the film properties, could be modified. The films obtained in this way had many properties in common with water-deposited films. They showed the same absorption band in the infrared, had comparable charge carrier densities and were electrically conductive (102 to 104 Sm-1 at room temperature). To our knowledge, this was the first time that such high electrical conductivities were achieved by sputtering in an oxygen plasma.

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