Alkali Metal Iodides Research Articles

Computer simulation of the electrical properties of carbon nanotubes encapsulated with alkali metal iodide crystals

The progress of modern electronics largely depends on the discovery and use of new materials with unique properties. One of such promising materials is carbon nanotubes. Their outstanding mechanical, thermal, and electrical properties open up new possibilities for creating small-sized electronic devices and improving the characteristics of existing materials by improving their manufacturing and processing technologies. One of the unique features of carbon nanotubes is their ability to encapsulate other atoms or molecules within their structure. This property can be used to create nanocontainers capable of protecting and transporting active substances or to change the electronic properties of nanotubes depending on the encapsulated substance. In this work, crystals of alkali metal iodides MI were encapsulated in carbon nanotubes with different structures and characteristics. The results obtained in terms of energy and density spectra of the state indicate the characteristics of conductivity due to an increase in energy and high peaks in the Fermi level. Thus, carbon nanotubes represent an important material for future developments in the field of nanoelectronics and nanotechnology.

Membrane‐Free Alkali Metal‐Iodide Battery with a Molten Salt

Batteries with liquid metal electrodes are attractive candidates for sustainable energy‐storage applications due to low manufacturing cost and high recyclability. These batteries should be developed for lower operating temperature, higher cell voltage, and membrane‐free cell configuration. Herein, a new type of a membrane‐free cell relying on liquid alkali metals and iodide is demonstrated. As a proof‐of‐concept study, membrane‐free alkali metal‐iodide (A‐AI) batteries are constructed by a facile cell assembly introducing current collectors, LiI–LiCl–KI–CsI salt mixture, and an insulator without relying on solid‐state mediums for separating electrolytes. For the initial assembly, no active electrode materials are required since they are naturally formed during battery operation. Despite the unoptimized cell construction, the membrane‐free A‐AI batteries show promising electrochemical performance such as a reliable stability for 250 cycles. The cells are able to handle a high current density and show a relatively low self‐discharge rate, which implies the possibility of an iodine‐concentrated layer at the bottom of the cell. This is further supported by postmortem analyses using neutron radiography. X‐ray photoemission spectroscopy is performed to identify the changes in the iodine concentration in the cell.

Dipolar effects on the work function of an alkali-iodide overlayer (XI, X = Li, Na, K, Rb, and Cs) on tungsten surfaces

A first-principles approach was used to investigate the effects of alkali metal iodide XI (X = Li, Na, K, Rb, and Cs) adsorption on the work functions of (100), (110), and (111) surfaces of W. For the most energetically stable structures, work functions and their corresponding electric dipole moment vectors were calculated. In agreement with available experimental measurements, it was verified that the formation of XI dipoles on the W surface causes the work function to decrease significantly. It was shown that the calculated XI dipoles are tilted with respect to the W surface for all systems. This contradicts earlier published suggestions that the surface electrostatic energy of the dipoles prevented them from being aligned along the surface and were instead normal to the surface. In our work it is shown that the orientations (tilt) and strengths of the dipole moments can be explained in terms of the internal strain caused by the alkali metal’s different atomic sizes and available surface area. What matters for the decrease in the work function is the component of the dipolar moment perpendicular to the surface. For all systems, the work function reduction was shown to be directly proportional to the normal component of the electric field created by these XI dipoles.

Technology for the Nondestructive Reprocessing of Sodium Iodide Technogenic Solutions into a Charge for Single Crystal Growth

Introduction. The production of NaI-based single crystals results in accumulation of great amount of liquid waste. To bring valuable constituents of this waste back, the NaI technogenic solutions are treated to precipitate iodine that is further used in the synthesis of high-pure NaI. However, the least contaminated part of the waste may be brought back into the main technological process without the intermediary stage of iodine destruction, which allows a considerable cost saving.Problem Statement. There have been no data on the effective purification coefficients for NaI solutions subsequently treated with barium hydroxide, sodium carbonate, and by mass crystallization. Requirements to impurity content, which NaI solutions have to comply with in order to be used in the nondestructive treatment have mot been not formulated.Purpose. The purpose of this research is to develop a technology for reprocessing NaI technogenic solutionsinto sodium iodide of high purity without NaI destruction at the intermediate stage.Material and Methods. The materials that have been used for this research are as follows: aqueous solutions of NaI-based crystal production waste, active coal, barium hydroxide, sodium carbonate. The methods that have been employed are the treatment of NaI solutions with barium hydroxide, sodium carbonate, and by mass crystallization. Results. The technology of NaI solution purification by treatment with barium hydroxide and sodium carbonate with further mass crystallization of the purified salt has been developed. This technology is more environment friendly and cheaper than the conventional one that includes obtaining pure iodine. A series of NaI technogenic solutions has been treated in laboratory conditions and on industrial equipment, and the efficiency of their purification by the chemical treatment and mass crystallization hasbeen estimated. The impurity content in the obtained salt and the scintillation parameters of grown NaI : Tl crystals meet the requirements for these products.Conclusions. The technology has been implemented in the manufacturing process at the pilot plant of the Institute for Scintillation Materials of the NAS of Ukraine. It may be used at other enterprises that deal with alkali metal iodide waste treatment.

Sonochemically synthesized cobalt oxide nanoparticles as an additive for natural polymer iodide electrolyte based dye-sensitized solar cells

Hydroxypropyl cellulose (HPC)-based gel polymer electrolytes with different alkali metal iodide salts (potassium iodide, KI; sodium iodide, NaI; and lithium iodide, LiI) were investigated. Electrochemical impedance spectroscopy (EIS) was used to examine the electrochemical properties of the electrolytes. The electrolyte containing KI salt (KI sample) has the highest ionic conductivity. The trend of conductivity of the samples developed as follows, KI > NaI > LiI. A hybrid gel polymer electrolyte (HGPE) was developed to further enhance the property by incorporating sonochemically synthesized cobalt oxide (Co3O4) nanoparticles into the KI sample. The nanoparticles were studied by field emission scanning electron microscopy (FESEM), high-resolution transmission electron microscopy (HRTEM), energy-dispersive X-ray spectroscopy (EDX), X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS). HGPEs containing various amounts of synthesized Co3O4 nanoparticles were examined with EIS, XRD, and Linear Sweep Voltammetry (LSV). The introduction of Co3O4 nanoparticles has improved the ionic conductivity, reduced activation energy and degree of crystallinity of the HGPEs. Dye-sensitized solar cells (DSSCs) assembled with the developed HGPEs have shown an improvement in short-circuit current density and efficiency. HGPE containing 7 wt% of Co3O4 nanoparticles achieved the best ionic conductivity and photovoltaic performance of DSSC of 8.02 mS cm−1 and 5.8%, respectively.

Eutectic iodide-based salt as a melem-to-PTI conversion stopping agent for all-in-one graphitic carbon nitride

The poor absorption of visible light and rapid recombination of photoexcited charge carriers are the two main factors responsible for the low photocatalytic activities of g-CN under sunlight. To mitigate these technical challenges, we utilize molten-salt synthesis based on alkali metal iodide. The high reactivity of LiI/KI does not allow the polycondensation of triazine dicyanamide intermediates further into PTI, the degree of which depends on the initial weight ratio of eutectic mixture to molecular precursor. This enables the controlled introduction of cyano functional groups with K+-coordination and decomposition of tri-s-triazine into triazine. The resulting all-in-one g-CN-I displays a photocatalytic hydrogen evolution reaction rate of 147 and 60 μmol/h from water under visible light and sunlight, respectively, which are 76 and 7 times higher than those of bulk g-CN. This study demonstrates the significant improvement in the photocatalytic activity of g-CN achievable through the synergistic combination of structural functionalities.

Alkali metal iodides and hydroiodic acid additives for phase-stability CsPbI<sub>3</sub> films prepared at low temperature

Inorganic cesium lead triiodide (CsPbI<sub>3</sub>) perovskite films show great prospect due to their high thermal stability and ideal band gap energy. To be used as a photovoltaic absorber, the CsPbI<sub>3</sub> must form the black phase (α-CsPbI<sub>3</sub>). To prepare high-quality CsPbI<sub>3</sub> films with phase stability in air at low temperatures, alkali metal iodides and hydroiodic acid (HI) additives are added into precursor solution. The results show that the quality and the phase stability of CsPbI<sub>3</sub> with alkali metal iodides and HI additives are obviously improved compared with those with only HI additive. The SEM images show that the CsPbI<sub>3</sub> film with 2.5% KI additive becomes more compact than that without KI additive and has no visible pinholes. As the KI additive increases, pinholes start to appear. From the XRD, it can be seen that the crystallinity of perovskite is improved when KI additive increases to 5.0%, while it starts to decrease with KI additive further increasing. The PL intensity of the CsPbI<sub>3</sub> film with 2.5% KI additive is higher than the others’, implying a relatively low non-radiative recombination loss and low defect state in that film. And the CsPbI<sub>3</sub> film with 2.5% KI additive exhibits increased absorption in the visible region, which is beneficial to enhancing the efficiency of perovskite solar cells. Considering the SEM images, crystallinity, PL intensity and light absorption of perovskite, the optimized KI additive is 2.5% in our work. For the CsPbI<sub>3</sub> film with NaI additive, the SEM images show that the films become more compact and have no visible pinholes when NaI additive is 5%. As the NaI additive increases, pinholes appear. The crystallinity of perovskite increases with NaI additive increasing. The PL intensity of the CsPbI<sub>3</sub> film with 5% NaI additive is higher than the others’, implying lower defect states in films. And the CsPbI<sub>3</sub> film with 5% NaI additive exhibits the improved absorption in the visible region. Considering the SEM images, crystallinity, PL intensity and light absorption of perovskite, the optimized NaI additive is 5%. Therefore, adding alkali metal iodides and HI is an effective method to further improve the stability and efficiency of CsPbI<sub>3</sub> perovskite solar cells.

Specific carbon/iodide interactions in electrochemical capacitors monitored by EQCM technique

This paper reports on the ion fluxes at the interfaces of various porous carbon electrodes/aqueous solutions of alkali metal cations (Na+, K+ and Rb+) and iodide anions, monitored by an electrochemical quartz crystal microbalance (EQCM).

An Electrochemical Approach toward the Metastable Type II Clathrate Germanium Allotrope.

By using an anodic conversion process at 280 °C, the type II clathrates Na1.7(6)Ge136 and Na23.0(5)Ge136 were obtained from Na12Ge17 as the starting material. An alkali-metal iodide molten-salt electrolyte complied with the reaction conditions, allowing for the formation of microcrystalline products. Characterization by powder X-ray diffraction, scanning electron microscopy, and energy-dispersive X-ray spectroscopy also revealed Na4Ge13 as an intermediate and α-Ge and Cs8–xGe136 as byproducts, with the latter likely resulting from cation exchange between the starting material and electrolyte. Taking such minor side reactions and a small contribution of material without suitable electrical contact into account, anodic conversion of Na12Ge17 to Na1.7Ge136 proved to proceed without parasitic processes and to comprise the material bulk. The hitherto existing preparation method for Nax→0Ge136 by gas–solid oxidation of Na12Ge17 has thus been translated into a scalable high-temperature electrochemical approach with enhanced tools for reaction control, promising access to pure Ge(cF136) and Na24Ge136 after process optimization.

Review on mixed cation effect in gel polymer electrolytes for quasi solid-state dye-sensitized solar cells

This paper reviews the efforts made to enhance the power conversion efficiencies of dye-sensitized solar cells (DSCs) by employing binary and ternary iodides in gel polymer electrolytes. Reported studies about mixed cation effects in quasi-solid-state electrolytes have been investigated using polyacrylonitrile (PAN), polyvinylidene fluoride, polyvinyl alcohol, polyethylene oxide, polymethylmethacrylate, and phthaloylchitosan as host polymers, with PAN being the most commonly employed. Ionic conductivities, their dependence on the composition of iodide salts, and the nature of counterion have been studied by preparing many different sets of gel polymer electrolytes. DSCs that were fabricated and characterized using different gel polymer electrolytes containing binary salt combinations showed efficiency enhancements. The general trend of open-circuit voltage (Voc) is to increase with an increasing radius of counterion, while short-circuit current density (Jsc) tends to be enhanced with reducing the size of the counterion in the cell. This behavior has been confirmed by studying single salt systems based on alkali metal iodides as well as quaternary ammonium iodides. The studies emphasized a significant enhancement of cell performance for binary cationic systems with respect to their single cation counterparts. In conclusion, the efficiency of the DSCs can be improved by employing a mixed cationic system with high and low charge densities.

Ion aggregation in complexes of alkali metal iodides and poly(ethylene oxide) or pentaglyme studied by molecular dynamics

Classical molecular dynamics simulations with polarizable force field have been performed for solid electrolytes based on poly(ethylene oxide) or pentaglyme and alkali metal iodides MeI (Me = Li, Na, K, Rb and Cs) in order to study salt precipitation process. Monitoring of structural changes has shown that the tendency for ion aggregation increases with the radius of the cation and with increasing temperature, in qualitative agreement with available experimental data. Analysis of estimated ion diffusivities and conductivities of studied electrolytes has revealed that simulations overestimate correlation between movements of oppositely charged ions compared to experiment. Possible improvements in simulation setup and directions for future more detailed studies have been proposed.

Generation of Alkali Metal Iodide Aerosols with Glycerin for Inhalation

Abstract—The article describes a method of generating bioactive alkali metal iodide aerosol particles with glycerin for inhalation; the particles have a diameter of d ≈ 0.03–3 µm and a mass productivity of m = 10–200 µg/s. A delivery device has been created.

Cu(II) complexes derived from N-carboxymethyl and N-carboxyethyl amino acids as catalysts for asymmetric oxidative coupling of 2-naphthol

The synthesis, characterization and catalytic performance of chiral Cu(II) complexes derived from N-carboxymethylated and N-carboxyethylated amino acids is reported. The ligand precursors are prepared by single step N-alkylation of the sodium salts of the appropriate chiral amino acid with either sodium chloroacetate or sodium 3-chloropropionate in water. The Cu(II) complexes are obtained upon reaction of Cu(CH3COO)2 with the aqueous or alcoholic suspension of the suitable ligand under vigorous stirring or ultrasound irradiation at room temperature. The Cu(II) compounds are characterised by EPR, UV–vis, circular dichroism and ESI-MS. The molecular structures of two of the prepared complexes are also obtained by single-crystal X-ray diffraction analysis. The catalytic activity of the complexes in the asymmetric oxidative coupling of 2-naphthol is described. All compounds exhibit moderate activity, selectivity and enantioselectivity in ethanol/water mixtures, under aerobic conditions and using potassium iodide as additive. The yields of 1,1′-bi-2-naphthol (BINOL) reached 50% under the optimal conditions, while enantiomeric excesses reached ca. 48%. The effect of variables such as ligand substituents, solvent, temperature and additives on the catalytic activity is also described. In the absence of a base, the complexes only show catalytic activity in the presence of alkali metal iodide such as KI. Details of the oxidative coupling mechanism are studied using spectroscopic and electrochemical methodologies.

Iodine-assisted control of the pore and morphology in the porous carbons prepared by the carbonization of ion-exchange resins

Abstract In this study, iodine stabilization treatment was employed to prepare spherical porous carbons by the carbonization of the Na+-form and K+-form of acrylic ion-exchange resins. Iodine treatment led to the increased carbonization yield of carbon and the successful maintenance of the bead shape of the raw resin. The as-obtained carbons contained by-products such as alkali metal carbonate or iodide. The removal of these salts with water led to carbons with well-developed porous structure. In addition, the pore size distribution and surface area changed with the variation in the iodine treatment time and carbonization temperature. The 1-h iodine-treated K+-form resin was converted to spherical carbon with the highest surface area of around 2000 m2/g at a carbonization temperature of 800 °C. Above this temperature, meso/macropores were introduced because of the considerable emphasis of the activation effect of the by-products.

Stable iodide doping induced by photonic curing for carbon nanotube transparent conductive films

Doping has become crucial for achieving stable and high-performance conductive transparent carbon nanotube (CNT) films. In this study, we systematically investigate the doping effects of a few materials including alkali metal iodides, nonmetal iodide, and metals. We demonstrate that photonic curing can enhance the doping effects, and correspondingly improve the conductivity of CNT films, and that such iodides have better doping effects than metals. In particular, doping with a nonmetal compound (NH4I) shows the largest potential to improve the conductivity of CNT films. Typically, doping with metal iodides reduces the sheet resistance (RS) of CNT films with 70–80% optical transmittances at λ = 550 nm from 600–2400 to 250–440 Ω/square, whereas doping with NH4I reduces RS to 57 and 84 Ω/square at 74 and 84% optical transmittances, respectively. Interestingly, such a doped CNT film exhibits only a slight increase in sheet resistance under an extreme environment of high temperature (85 °C) and high relative humidity (85%) for 350 h. The results suggest that photonic-curing-induced iodide doping is a promising approach to producing high-performance conductive transparent CNT films.

Preparation and characterizations of PMMA-PVDF based polymer composite electrolyte materials for dye sensitized solar cell

Blend polymer composite gel electrolytesare prepared using thepoly vinyledene fluoride (PVDF), polymethyl methacrylate (PMMA) with alumina (Al2O3) in variance of alkali metal iodide saltsystem. The alumina doped blend polymer electrolytes characterized by the XRD diffraction and FT-IR spectra. This is supportive to the conformation of the crystallinity behaviour and the composite formation.The high-resolution scanning electron microscopy (HR-SEM) have used to find the composite electrolyte membrane porous size (10 μm) and it has support to understand the morphological structure of the membrane. To analyze the ionic conductivity of the potassium iodide based composite polymer electrolyte by the impedance measurements, which is 4.62 × 10−3 Scm−1 at room temperature. Finally, different alkali metal iodide based dye-sensitized solar cells (DSSCs) fabricated and monitored an energy conversion efficiency.

Universal Approach toward Hysteresis-Free Perovskite Solar Cell via Defect Engineering.

Organic-inorganic halide perovskite is believed to be a potential candidate for high efficiency solar cells because power conversion efficiency (PCE) was certified to be more than 22%. Nevertheless, mismatch of PCE due to current density (J)-voltage (V) hysteresis in perovskite solar cells is an obstacle to overcome. There has been much lively debate on the origin of J-V hysteresis; however, effective methodology to solve the hysteric problem has not been developed. Here we report a universal approach for hysteresis-free perovskite solar cells via defect engineering. A severe hysteresis observed from the normal mesoscopic structure employing TiO2 and spiro-MeOTAD is almost removed or does not exist upon doping the pure perovskites, CH3NH3PbI3 and HC(NH2)2PbI3, and the mixed cation/anion perovskites, FA0.85MA0.15PbI2.55Br0.45 and FA0.85MA0.1Cs0.05PbI2.7Br0.3, with potassium iodide. Substantial reductions in low-frequency capacitance and bulk trap density are measured from the KI-doped perovskite, which is indicative of trap-hysteresis correlation. A series of experiments with alkali metal iodides of LiI, NaI, KI, RbI and CsI reveals that potassium ion is the right element for hysteresis-free perovskite. Theoretical studies suggest that the atomistic origin of the hysteresis of perovskite solar cells is not the migration of iodide vacancy but results from the formation of iodide Frenkel defect. Potassium ion is able to prevent the formation of Frenkel defect since K+ energetically prefers the interstitial site. A complete removal of hysteresis is more pronounced at mixed perovskite system as compared to pure perovskites, which is explained by lower formation energy of K interstitial (-0.65 V for CH3NH3PbI3 vs -1.17 V for mixed perovskite). The developed KI doping methodology is universally adapted for hysteresis-free perovskite regardless of perovskite composition and device structure.

Synthesis of CF3-containing oxazolines via trifluoromethylation of allylamides with Togni reagent in the presence of alkali metal iodides

We report an efficient synthetic method for CF3-containing oxazolines via trifluoromethylation of allylamides by using Togni reagent in the presence of alkali metal iodides, which play a key role in selective production of the desired oxazoline. The reaction did not proceed efficiently with copper catalysts commonly used for oxytrifluoromethylations. Our method afforded a wide variety of CF3-containing oxazolines, which are potential candidates for pharmaceuticals, agrochemicals, and functional materials.

Field-effect transition sensor for KI detection based on self-assembled calixtube monolayers

A series of novel calixarene-based tubes comprising different numbers of silatrane anchoring groups was synthesized. For the first time, a self-assembled monolayer (SAM) derived from calixtubes was formed on a SiO2 surface. The formation of the SAM was confirmed by X-ray photoelectron spectroscopy, scanning electron microscopy-energy dispersive X-ray analysis, and contact angle measurements. Modification of the sensitive surface of a conventional ion-selective field effect transistor (ISFET) with the afforded SAM resulted in the production of a KI-sensitive sensor. This sensor selectively determined KI compare to different alkali metal iodides: NaI, RbI, CsI; also investigation of different potassium salts (acetate, iodide, nitrate, chloride, dihydrophosphate, perchlorate) showed the highest response to KI. This sensor was successfully employed to determine the presence of KI in artificial saliva with a limit of detection of ~3 × 10−8 М. In addition, it was found that the detection limit of the sensor could be increased by combining the sensor with a microfluidic system. Due to the obtained sensor sensitivity and its ability to detect KI in artificial saliva, we could conclude that this sensor shows great potential for application in the determination of KI in different media, such as the human body and in biological liquids, such as saliva or urine.

Modeling activity coefficients in alkali iodide aqueous solutions using the extended Debye-Hückel theory

A recently developed extended Debye-Hückel (EDH) theory which allows for concentration variation of electrolyte solution static permittivity (I.Yu. Shilov, A.K. Lyashchenko, 2015) is employed to predict activity coefficients in alkali metal iodide (LiI, NaI, KI, and CsI) aqueous solutions at ambient conditions. Calculations without parameter fitting have shown a semiquantitative agreement with experimental data, reproducing the nonmonotonic concentration dependence of activity coefficients for LiI, NaI, and KI solutions. A good agreement with experimental data was obtained for NaI-water mixtures in the concentration range up to 7mol/kg. The correct ordering of activity coefficients for the salts with different cations was also reproduced and explained as resulting not only from decreasing solvation in the series LiI>NaI>KI>CsI but also due to increasing ion pairing with increasing cation size. The applicability limits of the EDH theory are outlined.