Graduate Studies of Global Change at the University of Latvia

In 2008 the University of Latvia (UL) completed an 18-month project of innovation – design, preparation and pilot-test of a 4-semester programme of trans-disciplinary graduate studies in “science, global change, and technologies for sustainable development” based on the experience the project team had acquired during 1997–2006 endorsing studies in “physics and technologies for sustainable development” and organizing two international conferences on “integrative approaches towards sustainability”. Within the project activities 25 members from faculties of natural sciences of the UL prepared and tested innovative courses of a 2 semester pilot programme comprising 4 modules, the audience being…

A Comparative Study of Natural Fiber and Glass Fiber Fabrics Properties with Metal or Oxide Coatings

Rapidly growing global demand for technical textiles industries is stimulated to develop new materials based on hybrid materials (yarns, fabrics) made from natural and glass fibres. The influence of moisture on the electrical properties of metal and metal oxide coated bast (flax, hemp) fibre and glass fibre fabrics are studied by electrical impedance spectroscopy and thermogravimetry. The bast fibre and glass fiber fabrics are characterized with electrical sheet resistance. The method for description of electrical sheet resistance of the metal and metal oxide coated technical textile is discussed. The method can be used by designers to estimate the influence of moisture on technical data of…

Electrochemical performance of Na2FeP2O7/C cathode for sodium-ion batteries in electrolyte with fluoroethylene carbonate additive

Abstract Solution synthesis was used to prepare pristine Na2FeP2O7 and Na2FeP2O7/C composite cathode materials for sodium-ion batteries, using glucose as a carbon source. While the pristine Na2FeP2O7 displays capacity of only 45 mAh/g due to the relatively large grain size, the addition of carbon increases the capacity to up to 92 mAh/g (95% of the theoretical 97 mAh/g capacity) with excellent rate capability, as 44 mAh/g capacity is still retained even at 20 C (1.94 A/g) current. The optimal content of carbon was found to be 4.8%. The initial capacity of 81 mAh/g is fully retained after 500 cycles at 1 C, indicating excellent cycle life. Measurements were carried out in 1 M NaClO4 salt in …

Graphene in lithium ion battery cathode materials: A review

Abstract Graphene is a relatively new and promising material, displaying a unique array of physical and chemical properties. Although considered to be especially promising for the use in energy storage applications, graphene has only recently been implemented as an electron conducting additive for lithium ion battery cathode materials. In current studies graphene is found to significantly improve cathode electrochemical performance. As the charge capacity, rate capability and cyclability of lithium ion batteries are still in ever-remaining need of improvement, this article examines the prospects of graphene implementation into lithium ion battery cathodes to meet such demands. The existing …

Preparation and photoactivity of electrophoretic TiO2coating film

TiO2 thin films have been obtained by a sol-electrophoretic deposition method on metallic Ti and Pt substrates. X-ray diffraction, Raman spectroscopy and scanning electron microscopy were used to investigate the structure and morphology of plated materials. Annealed TiO2 films mainly are formed in anatase structure with different morphology depending on substrate material. Light induced potential measurements indicate that the morphology substantially have an impact on photoactivity of TiO2 thin films.

Nanostructured LiCoO2 Cathode by Hydrothermal Process

Investigation of carbonized layer on surface of NaAlSi glass fibers

There are presented and discussed experimental results about carbonate shell on the sodium rich alumosilicate (NaAlSi) glass fibers and carbonization in wet air atmosphere and water uptake kinetic of such fiber fabrics. The analyzes of water uptake kinetic by regression technique, leaching and heating of carbonized glass fabrics helped to separate stages of fast and slow processes between fiber and carbonate shell and air atmosphere. The shell contains mixture of trona and hydrated sodium carbonate. Heating converts both substances to sodium carbonate. The weight uptake after heating encounters two fast exponential processes associated with water absorption on the surface of carbonated shel…

Electrolyses model development for metal/electrolyte interface: Testing with microrespiration sensors

Abstract Initial process of electrolysis is investigated using platinum and tungsten wires as hydrogen electrodes and inductive kickback voltage peak based power unit. Microelectrodes are used to determine concentrations of dissolved hydrogen and pH close to wire electrodes. It is observed that concentration of dissolved hydrogen increases faster on tungsten electrode as on platinum. Authors explain this fact with differences of hydrogen evolution reaction on both materials – inductive kickback voltage peak power unit is supplying very short voltage pulses with limited energy what is enough only for hydrogen adsorption on platinum electrode, but is sufficient for full hydrogen evolution rea…

Mass recovery of carbonated fabrics of glass fibres after isothermal heating

Acknowledgement: Authors acknowledge financial support from Latvian National Program IMIS2

Electrochemical impedance and moisture content of glass fabric

The glass fiber fabrics have application at the wet conditions. Impedance measurements of sodium alumosilicate glass fabric in dependence on its moisture content are presented. The impact of pores of glass fibres and fabric components to electrochemical impedance of fabric are investigated and discussed.

Preparation and Characterization of Nanostructured Fe-TiO2 Thin Films Produced by Electrophoretic Deposition

Fe-TiO2 thin films have been produced by a sol-electrophoretic deposition method on metallic Ti foil substrates. X-ray diffractograms and Raman spectra confirms the anatase structure of deposited and annealed Fe-TiO2 films. Obtained Fe-TiO2 thin films demonstrate photoactivity under visible light radiation due to the doping with Fe3+ ions. Open circuit potential results shows that increase of the film thickness and surface area improves the photoactivity of Fe-TiO2.

<title>Influence of treatment on stability of electrochromic WO<formula><inf><roman>3</roman></inf></formula> film in acidic electrolyte</title>

The influence of exposure in vacuum of 10-2 - 10-3 Pa and temperature treatment at 720 - 730 K in water vapor atmosphere on stability of tungsten oxide films in 0.1 N H2SO4 electrolyte were studied. The processes that take place during the film exposure in vacuum, determine the reduction of charge injection at the constant voltage change condition. In the case of temperature treatment the opposite changes of charge injection were observed. This indicates to opposite processes in films during both expositions. According to exposures characters, they could be a reduction of tungsten oxide initiated by oxygen evacuation from film in vacuum and film oxidation in water vapor media at high temper…

<title>Long-term testing results of WO<formula><inf><roman>3</roman></inf></formula>-based electrochromic cells</title>

Two batches of the samples of electrochromic cell with WO3 and IrOx electrodes and Sb2O5 (DOT) water based solid electrolyte were tested at constant contrast ratio up to 107 cycles or stored during five years and the changes of current-voltage characteristics were studied. Two kinds of the changes were observed. The shift of curves along the voltage axis is supposed to be associated with the changes in the oxidation degree of tungsten oxide, while the changes in their shapes are associated with changes of water content in pores. The processes in the samples during cycling and storing are discussed.© (1997) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the…

Structure and Photocatalytic Properties of TiO2-WO3Composites Prepared by Electrophoretic Deposition

In this work TiO2-WO3 composite films containing different oxide concentrations were prepared by electrophoretic deposition on steel substrates. Composite coating structures were analyzed by X -ray diffraction, Raman spectra and scanning electron microscopy. The results showed an even distribution of WO3 particles in the entire composite layer. Light absorption measurements were used for photocatalytic properties evaluation. It was found that the removal ratio of methylene blue depends on the (TiO2):(WO3) concentration ratio. The most effective photodegradation was determined for the sample that was electrophoretically deposited from the suspension with the molar content ratio n(TiO2):n(WO3…

Estimation of hydrogen transfer mechanisms in composite materials

Abstract Spill-over effect as a hydrogen transfer mechanism is proposed to explain an increased capacity of hydrogen absorption and improvement of hydrogen activation kinetics in composite material based on the AB5 type metal hydride and powdered glass. A raw lanthanum nickel alloy AB5 with small amount of additives was used as catalyst and bulk material for hydrogen storage, and a borosilicate glass powder with developed surface was applied as a support material. Thermogravimetric technique to determine an absorbed amount of the hydrogen in materials and X-ray powder diffraction analysis for structural investigations was used.

WO 3 as Additive for Efficient Photocatalyst Binary System TiO 2 /WO 3

The financial support provided by Scientific Research Project for Students and Young Researchers No. SJZ/2018/9 implemented at the Institute of Solid State Physics, University of Latvia is greatly acknowledged. Institute of Solid State Physics, University of Latvia as the Center of Excellence has received funding from the Euro-pean Union’s Horizon 2020 Framework Programme H2020-WIDESPREAD-01-2016-2017-TeamingPhase2 under grant agreement No. 739508, project CAMART².

Physical and electrochemical properties of LiFePO4/C thin films deposited by direct current and radiofrequency magnetron sputtering

Abstract In this study, LiFePO 4 /C thin films with various contents of carbon were prepared by direct current (DC), radiofrequency (RF) and combined (DC/RF) magnetron sputtering methods. Influences of the composition, morphology and microstructure on the electrochemical properties of LiFePO 4 /C thin films are investigated by studying charge–discharge curves, cyclic voltammetry and electrochemical impedance spectroscopy. Cyclic voltammogram of the LiFePO 4 /C thin film showed the typical redox reaction peaks characterizing the electrochemical lithium insertion/extraction reactions in LiFePO 4 . Obtained LiFePO 4 /C thin films have relatively high charge capacities (127 mAh g − 1 ). It was …

Characterization of LiFePO4/C Composite Thin Films Using Electrochemical Impedance Spectroscopy

The composite LiFePO4/C thin films were prepared on steel substrate by radio frequency (RF) magnetron sputtering. Electrochemical properties of the obtained thin films were investigated by cyclic voltammetry charge-discharge measurements and electrochemical impedance spectroscopy (EIS). The films annealed at 550 °C exhibited a couple of redox peaks at 3.45 V vs. Li/Li + characteristic for the electrochemical lithium insertion/extraction in LiFePO4. At low current rate such composite thin film showed a discharge capacity of over 110 mAh g -1 . The dependence of charge transfer resistance, double layer capacitance and lithium diffusion coefficients on applied electrode potential were calculat…

Gaseous sensors based on solid proton conductors

Abstract he chemical sensors for different gaseous (alcohol, acetone, ammonia, water vapour) detection at room temperature are developed by using polycrystalline β-alumina and xerogel of antimonic acid hydrate (AAH). The sensitivity and selectivity of sensors depend on the ion-exchange and preparative methods. The possibility of producing different types of potentiometric, amperometric, voltammetric and resistance sensors on the basis of these ion-conducting materials is shown. More success is achieved by producing ammonia-sensitive devices on β-alumina as well as on AAH xerogel.

Electrophoretic Nanocrystalline Graphene Film Electrode for Lithium Ion Battery

Graphene sheets were fabricated by electrophoretic deposition method from water suspension of graphene oxide followed by thermal reduction. The formation of nanocrystalline graphene sheets has been confirmed by scanning electron microscopy, X-ray diffraction and Raman spectroscopy. The electrochemical performance of graphene sheets as anode material for lithium ion batteries was evaluated by cycling voltammetry, galvanostatic charge-discharge cycling, and electrochemical impedance spectroscopy. Fabricated graphene sheets exhibited high discharge capacity of about 1120 mAhg−1 and demonstrated good reversibility of lithium intercalation and deintercalation in graphene sheet film with capacity…

Environment Humidity Effect on the Weight of Carbonized Na-Al-Si Glass Fabrics Recovery after Heating

Na-Al-Si glass fabrics fibres contain Na+ ions that diffuse to its surface and along with CO2 and H2O from atmosphere create here the shell of carbonate hydrates. The heating of fabric leads to weight loss by evolving these substances. In this work the results of weight recovery study at room relative humidity (20% – 50%) and elevated humidity (near 70%) of fabrics after its heating at different temperatures (70°C – 150°C) are compared. The experiments shoved the different weight recovery kinetics. The initial exponential stages up to 0.3 h – 0.5 h of the both recoveries are associated with water absorption and differ by its levels. In a case of lower environment humidity the later weight i…

Study the effects of moisture content on the electrical properties of technical textiles by impedance spectroscopy

Application of metal coatings for the functionalization of technical fibres and fabrics faced with influence of moisture on functional properties, e.g., the impedance of the metal coated K-glass fabrics have strong dependence of content absorbed water or moisture. The paper devoted to develop methodology for characterisation functional materials based on fabrics and model for interpretation of the electrical impedance spectra to obtained functional characteristics of technical textile fabrics. Model based on analyses of 3D plot of imaginary part of complex modulus spectra versus sample mass. Methodology helps to control content of adsorbed water in fabric and influence of moisture on the fu…

Electrophoretically deposited α-Fe2O3 and TiO2 composite anchored on rGO with excellent cycle performance as anode for lithium ion batteries

Abstract Two nanostructured oxides, α-Fe2O3 and TiO2 with a particle diameters 50 nm and 21 nm, were mixed with graphene oxide (GO). Composite thin films on a stainless steel substrate were obtained by electrophoretic deposition (EPD) procedure from water suspensions: α-Fe2O3/GO, TiO2/GO and α-Fe2O3/TiO2/GO. Subsequently reduction of as-prepared thin films was performed. Thicknesses of acquired films were evaluated in the range of 2–6 μm. Structure and morphology were investigated as well as electrochemical properties of all samples were studied. The results revealed that α-Fe2O3/TiO2/rGO (in this article denoted as FTGO) exhibited the specific discharge capacity of 790 mAh·g−1 after 150 cy…