Yttrium-doped hematite photoanodes for solar water splitting: Photoelectrochemical and electronic properties

Abstract We investigate yttrium-doped hematite thin-film photoelectrochemical properties and find yttrium incorporation to amply improve the performance as a photoanode for water splitting under visible light. We used the spray pyrolysis method to prepare a set of yttrium doped Fe2-xYxO3 (x = 0, 0.05, 0.10, 0.15, 0.2) thin films (thickness below 500 nm) on glass and transparent conductive oxide coated glass slides. Using a substitutional homovalent (Y3+) dopant, the effect on functionality is rationalised as a combined effect on the electronic structure and small polaron mobility from the lattice structure, impurity levels, lattice stability and variance in hybridisation. The photoelectroch…

First Steps of µTAS in Latvia

Owing to participation of Latvian and Swedish scientists in the field of chemically sensitive FET and MOS structures it was possible to utilize the technological facilities of the Microelectronics enterprise in Latvia in making an integrated smart sensor as a matrix of chemically sensitive FETs by using silicon based microtechnology. Thereby the first steps of µTAS in Latvia are made in the direction of integration of solid state ionic materials with FET and MOS structures to develop new chemically sensitive structures and systems.

Synthesis and studying of reduced few-layered graphene coatings in gas sensor applications

In this work reduced few-layered graphene (rFLG) nanoparticles were synthesized using electrochemical pulse exfoliation method from waste graphite crucibles. The regular change in voltage polarity in the synthesis process ensures both the separation of graphite in layers and the reduction of graphene oxide. A method for synthesizing free-standing rFLG and nitrocellulose (NC) composite film has been developed involving creation of rFLG-NC ink that can be deposited on various substrates. It has been observed that a successful synthesis of a free-standing composite coating is possible with the mass ratio of rFLG:NC at least 9:1 of which resistivity is on the order of approximate 10 ohm-centime…

Changes in freshwater sediment microbial populations during fermentation of crude glycerol

This work was supported by the Latvian Council of Science , project NN-CARMA, project No. lzp-2018/1-0194.

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 …

TRAFFIC FLOW HYPOTHETICAL MODELLING FOR AIR QUALITY IMPROVEMENT AND PLANNING PURPOSES

The main emphasis of this research was to describe air pollution level and dispersion in a typical street canyon (Valdemara Street in Riga (Latvia) city centre), afterward to postulate potential development scenarios and perform modelling in order to understand the influence on air pollution level. For this purpose special mathematical model was used - Operational Street Pollution Model (OSPM), which was developed by the National Environmental Research Institute in Denmark. Following development scenarios were tested: (1) realistic environmentally friendly - decrease of traffic flow by 50 %, as according to street interviews about 36 - 50 % of drivers are ready to change driving habits from…

Ab initio calculations of CaZrO3 (011) surfaces: systematic trends in polar (011) surface calculations of ABO3 perovskites

Financial support via Latvian-Ukrainian Joint Research Project No. LV-UA/2018/2 for A. I. Popov, Latvian Council of Science Project No. 2018/2-0083 “Theoretical prediction of hybrid nanostructured photocatalytic materials for efficient water splitting” for R. I. Eglitis and J. Kleperis as well as ERAF project No. 1.1.1.1/18/A/073 for R. I. Eglitis and J. Purans is greatly acknowledged.

Influence of the initial acidification step on biogas production and composition

Laboratory-scale experiments were carried out to evaluate the effect of initial acidification of feedstock consisting of different components on biogas production and composition. Feedstock containing different agricultural wastes, biomass, and microorganisms was collected from five full-scale biogas plants. Two continuously stirred tank reactors were used. The fermentation temperature was 37 °C. The pH value was adjusted to 6.0 in the first reactor at the beginning of the experiment, and an initial pH value of 7.0 was implemented after 48 H. The second reactor was used as a control reactor with a constant pH of 7.0. The experiment lasted a total of 7 days. In the reactors, the gas phase wa…

Nafion® and polyaniline composite modification with Li and Mg ions

Funding from European Union`s Horizon 2020 Research and Innovation Program project under grant agreement No 768789 is greatly acknowledged.

<title>Proton conducting polymer electrolytes for electrochromic devices</title>

This report concerns a composite proton electrolyte suitable for use in electrochromic devices. The electrolyte consists of nanosize hydrated oxide (aluminum, silicon or antimonic) particles suspended in a poly(vinyl acetate) matrix. All of the water was strongly bonded, thus making the electrolytes less harmful without considerably decreasing the conductivity. The proton conductivity of the electrolyte was approximately 10-4 S/cm at room temperature, practically independent of its amount of absorbed water.© (1997) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.

AC impedance behavior of the Ti4Ni2Oy and Ti3.5Zr0.5Ni2Oy type metal hydride electrodes

The hydrogen storage alloy electrodes of the type Ti4Ni2Oy (y=0, 0.3 and 0.6) and Ti3.5Zr0.5Ni2Oy (y=0.15 and 0.3) were investigated by impedance spectroscopy for potential application as negative electrode in alkaline secondary nickel-metal hydride (MH) batteries. The phase Ti4Ni2O0.30 was found to be electrochemically more stable during the cycling. The addition of copper or nickel powder as current collector improved the electrochemical behavior of the electrodes. It was possible in this way to decrease the charge transfer resistance. These additions have a negligible influence on the stability of electrode material during cycling.

Study of the structural phase transformation of iron oxide nanoparticles from an Fe2+ ion source by precipitation under various synthesis parameters and temperatures

Abstract Magnetite nanoparticles were precipitated from a pure aqueous ferrous salt solution in an air atmosphere. The influence of the solution molarity, the rate of precipitator agent addition, stirring time and annealing temperature was studied. The morphology, crystalline phase purity and magnetic properties of the obtained powders were studied by X-Ray powder diffraction (XRD), Scanning electron microscopy (SEM), Differential thermal analysis (DTA), X-ray photoelectron spectroscopy (XPS), X-ray absorption spectroscopy (XAS) and Vibrating sample magnetometer (VSM). The synthesis conditions were seen to have an effect on phase composition. It was possible to obtain near stoichiometric Fe…

Photocatalytic activity of anatase-nickel ferrite heterostructures

The simple co-precipitation route was used to couple commercial TiO2 anatase nanopowder with nickel ferrite (NiFe2O4). The morphology and the crystalline structure of composite nanoparticles were characterised by TEM, N2 adsorption-desorption, XRD and Rietveld refinement, XPS and XAS. The optical and magnetic properties were investigated. After co-precipitation NiFe2O4 nanoparticles, composed of spinel ferrite crystal phase, were formed on the surface of TiO2 anatase nanopowder. The TiO2/NiFe2O4 composite oxide demonstrated large specific surface area, high visible light absorption efficiency and efficient charge carrier separation, compared to pristine anatase TiO2 or pristine NiFe2O4, rep…

Modified Graphene Sheet Stacks for Hydrogen Binding

Results are partially obtained using infrastructure of Lithuanian Energy Institute with support of COST Action MP1103 “Nanostructured materials for solid-state hydrogen storage”. Latvian National Research program IMIS2 is greatly acknowledged for financial support

Prospects of Decarbonizing Industrial Areas in the Baltic States by Means of Alternative Fuels

This work has been supported by the National Research Programme, project “Trends, Challenges and Solutions of Latvian Gas Infrastructure Development” (LAGAS), No. VPP-EM-INFRA-2018/1-0003.

Electrochemical Studies of Nonstoichiometric TiO<sub>2-x</sub> Ceramic

TiO2 ceramic was prepared using extrusion technology and thermal treatment in two stages: sintering in air and subsequent annealing under high vacuum conditions. Sample thermal treatment in high vacuum conditions causes formation of nonstoichiometric titanium oxide ceramic. As a result electrical conductivity of the material significantly increases. Such a material can be used for electrode production for electrochemical water treatment.

AB Initio Calculations of CUN@Graphene (0001) Nanostructures for Electrocatalytic Applications

Funding from European Union’s Horizon 2020 Research and Innovation Programme project under grant agreement No. 768789 is greatly acknowledged.

Anodic biofilm vitality during operation of microbial fuel cells at various load conditions

Photo-Activity Research of Nano-Structured TiO2Layers

Titania with anatase structure is investigated due to its photo-active properties that can be used in the water photocatalysis applications and in the organic photovoltaic devices. In this work the anodization conditions are described to obtain stable thin film TiO2 layers formed from vertically oriented nanotubes with approximate height 358 nm, inner tube diameter 48 nm and wall thickness 20 nm, but centre to centre distance 100 nm. Annealed at 500 o C TiO2 layer mostly consists from oxide with anatase structure, though XRD spectroscopy shows rutile impurities as well. Obtained nanotube layers are sensitive mostly to UV light.

<title>Nature of fundamental absorption edge of WO<formula><inf><roman>3</roman></inf></formula></title>

The fundamental absorption edge of amorphous, polycrystalline and crystalline tungsten trioxide (WO3) thin films obtained by different techniques (thermal evaporation, rf plasma sputtering, chemical gas transport) was investigated. Special attention was paid to correct measurements of absorption values of all WO3 thin films taking into account the scattered light, interference effects and reflection losses. The indirect edge at 2.70 eV was determined for crystalline WO3, but for crystal WO3:Ti the direct edge in the same place (2.72 eV) was found. For polycrystalline WO3 thin film first edge transition located at 2.76 eV had a quadratic dependence similar to the amorphous film at a higher p…

Properties of the Nafion membrane impregnated with hydroxyl ammonium based ionic liquids

In this work, the Nafion 112 membrane impregnated with nine various hydroxyl ammonium based ionic liquids have been investigated. The used ionic liquids were combined from hydroxyl ammonium cations (2-hydroxyethylammonium/HEA, bis(2- hydroxyethyl)ammonium/BHEA, tris(2-hydroxyethyl)ammonium/THEA) and carboxylate anions (formate, acetate, lactate). The membranes are characterized by conductivity and thermal stability measurements. It was found, that almost all composites have 10 times higher ion conductivity than a pure Nafion 112 at 90 ?C in ambient environment due to the higher thermal stability. The thermal stability of Nafion membrane was increased by all studied nine ionic liquids. In th…

Raman spectral identification of phase distribution in anodic titanium dioxide coating

Growing need for cleaner environment and energy production has brought about a hunt for perspective materials. One of such perspective materials is titanium dioxide (TiO2, titania) due to its chemical stability and photocatalytic properties. Titania can be synthesized through many methods but anodization process is one of the prevailing methods to produce high active surface nanostructured titania. Various anodization electrolytes produce different polymorphs of TiO2. Uniform phase distribution on the surface is crucial for higher photocatalytic activity. In this research, the influence of two electrolytes on polymorph phase distribution of TiO2 was investigated. Phase distribution correlat…

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

Catalyst activation of silica nano-based pore structure material for hydrogen storage

Silica based composite material with palladium synthesized by extractive-pyrolytic method is used for hydrogen absorption-desorption experiments. The results obtained of the study on dynamic sorption experiments showed that Pyrex glass based composite sample reaches high hydrogen concentration in the material quite fast. Thought silica gel based composite material rapidly reaches 1/2 of hydrogen load but afterwards the amount of hydrogenation increases slowly. The overall amount of absorbed hydrogen for Pyrex glass based material exceeds the amount of absorbed hydrogen by silica gel based material approximately 5.6 times.

Evaluation of Local Scale PM Pollution Levels in Typical Street Canyon in Riga

The present study describes long term PM10 and PM2.5 changes in typical street canyon with particular emphasis on seasonal, diurnal variations in context with meteorological data. In order to understand PM10 pollution sources during 28 April 2007-31 December 2007, chemical composition measurements were done with particular emphasis on heavy metals (As, Cd, Ni, and Pb), crustal material (Ca, Mg, Na, and K) and anions (sulphates, nitrates, chlorides). Meteorological data used for this evolutional analysis were measured close to traffic related stations and several meteorological parameters were analyzed in relation to particulate measurements. Keep in mind that atmospheric aerosols are genera…

Analysis of the Role of the Latvian Natural Gas Network for the use of Future Energy Systems: Hydrogen from Res

The research has been funded by the Ministry of Economics of the Republic of Latvia, project “Trends, Challenges and Solutions of Latvian Gas Infrastructure Development (LAGAS)”, project No. VPP EM-INFRA-2018/1-0003.

Electrochemical exfoliation-streamline method for synthesis of nitrogen doped graphene

The authors gratefully acknowledge financial support from the Latvian Council of Science, Project LZP FLPP No. LZP-2018/1 0194, and the Institute of Solid State Physics, University of Latvia that as the Center of Excellence has received funding from the European Union’s Horizon 2020 Framework Programme H2020-WIDESPREAD-01-2026-2017-TeamingPhase2 under Grant Agreement No. 739508, Project CAMART2.

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…

Changes in Surface Free Energy and Surface Conductivity of Carbon Nanotube/Polyimide Nanocomposite Films Induced by UV Irradiation.

Changes in surface energy and electrical conductivity of polyimide (PI)-based nanocomposite films filled with carbon nanotubes (CNTs) induced by UV exposure are gaining considerable interest in microelectronic, aeronautical, and aerospace applications. However, the underlying mechanism of PI photochemistry and oxidation reactions induced by UV irradiation upon the surface in the presence of CNTs is still not clear. Here, we probed the interplay between CNTs and PIs under UV exposure in the surface properties of CNT/PI nanocomposite films. Changes in contact angles and surface electrical conductivity at the surface of CNT/PI nanocomposite films after UV exposure were measured. The unpaired e…

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 …

ChemInform Abstract: Electrochemical Behavior of Metal Hydrides

Metal hydride electrodes are of particular interest owing to their potential and practical application in batteries. A large number of hydrogen storage materials has been characterized so far. This paper deals with the effect of the chemical nature and stoichiometry of specific alloy families (AB5, A2B, AB/AB2 and AB2) on the hydride stability, hydrogen storage capacity and kinetics of hydrogen sorption-desorption in the solid phase/gas and solid phase/electrolyte solution systems. Special attention has been paid towards the electrochemical properties of metal hydrides in terms of their performance in Ni-MH rechargeable alkaline cells.

Wood and Black Liquor-Based N-Doped Activated Carbon for Energy Application

The research was funded by the Latvian Council of Science project “Nanostructured Nitrogenated Carbon Materials as Promoters in Energy Harvesting and Storage Technologies”, project No LZP-2018/1-0194, “New biomass origin materials hybrid carbon composites for energy storage” project No LZP-2020/2-0019 and postdoc project “Nitrogen and phosphorus-containing biomass based activated carbons for fuel cells and supercapacitors” project No 1.1.1.2/VIAA/4/20/596.

Traffic induced air pollution modeling: Scenario analysis for air quality management in street canyon

This study was supported by the Riga City research project DMV-17-60-lī-03.02.2017. The authors wish to thank the Riga City Council and Latvian Environment, Geology and Meteorology Centre for data used in this study.

<title>Performance problems of electrochromic coatings</title>

The performance is actual problem of electrochromic coatings. The service and shelf life and cycling capacity are main performance characteristics. By solid-state ionics point of view any electrochromic cell based on phenomena with ion insertion - extraction processes is functioning as solid-state rechargeable battery. The main performance characteristics of electrochromic cells are similar. Performance of electrochromic coatings based on amorphous WO3 films and protons conducting electrolytes is limited by reversibility of ion insertion-extraction reactions, which causes degradation of cell components. The migration of water in the cell and hydration together with ion insertion-extraction …

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…

<title>Properties of ITO transparent electrode thin films on different substrates</title>

Indium tin oxide (ITO) is optically transparent semiconductor that finds extensive applications in liquid crystal displays, photovoltaic cells, touch screen displays, electrochromic smart windows and more. As with all such electrode materials, there is a compromise between conductivity and optical properties. Different substrate materials and underlying layers are playing important role in transparency (better contrast and less absorption, increased brightness), surface morphology (smoothness, homogeneously) and conductivity of the ITO films. We compared optical, electrical and morphology properties of ITO films onto polymer substrate, obtained from company "SIDRABE Inc." (Latvia) and ITO f…

Properties of Multi Phase Interfaces on the Tungsten Trioxide Particles in the Thin Films

A wide spectrum of physical and chemical properties of thin films of tungsten trioxide compounds depend on composition, constitution and structure of the film, interaction with environment, and the type of external influences/excitations. The reason is the non-stoichiometric nature of transition metal oxides and properties of d-electrons. The short range order of non-stoichiometric compounds or phases of WO3 has a strong perovskite arrangement of tungsten and oxygen ions [1, 2]. The smallest crystalline clusters of perovskite short range order consist 6÷9 of [WO6]-octahedrons. One of the structural peculiarities-features of tungsten trioxide, related to non-stoichiometry, is a variety of [W…

Metal hydride alloys for storing hydrogen produced by anaerobic bacterial fermentation

Abstract This study reports on hydrogen sorption from bacterial fermentation media with powdered palladium (Pd) and alloys (LaNi5, AB5, and AB2) that are capable of forming hydrides. Mass changes of the powders after incubation in fermentation media were measured by differential thermogravimetry. Composition and concentrations of the gases accumulated during fermentation and absorbed by Pd or the alloys were analyzed by mass spectrometry. The results demonstrated that hydrogen (H2) was absorbed and stored by powdered Pd and alloys directly from nutritional broth. The best sorption was obtained with Pd, followed by alloys AB5 and AB2. Scanning electron microscopy revealed that bacteria were …

Comparison of the electrochemical properties of hematite thin films prepared by spray pyrolysis and electrodeposition

Abstract This manuscript reports differences between the photoelectrochemical (PEC) activity of hematite (α-Fe 2 O 3 ) photoanodes produced by cathodic electrodeposition (ED) and spray pyrolysis (SP) methods. Both methods yield nanostructured polycrystalline α-Fe 2 O 3 thin films without additional impurity phases. However, α-Fe 2 O 3 produced by ED is characterised to have better crystallinity and higher porosity, which was confirmed by XRD and SEM analysis. Owing to this, α-Fe 2 O 3 obtained by ED generates a photocurrent that is 2.5 times higher than α-Fe 2 O 3 thin films prepared by SP. Furthermore, the influence of the thickness of the α-Fe 2 O 3 thin films on the flat-band potential p…

CO2 and CH2 Adsorption on Copper-Decorated Graphene: Predictions from First Principle Calculations

Calculations were performed using Latvian Super Cluster (LASC), located in Center of Excellence at Institute of Solid State Physics, the University of Latvia, which is supported by European Union Horizon2020 Framework Programme H2020-WIDESPREAD-01-2016-2017-TeamingPhase2 under Grant Agreement No. 739508, project CAMART2. The authors would like to express their gratitude for funding from the European Union’s Horizon 2020 research and innovation programme under grant agreement No 768789 (CO2EXIDE project). In the last stage of investigation and during the preparation of the publication, the authors were assisted by the postdoc D.B. with his own funding from project No. 1.1.1.2/VIAA/l/16/147 (…