Affordable price, high abundance of magnesium and high densities of hydrogenin the Mg-based hydrides attract interest to these hydrides tailored for hydrogenand energy storage applications. Ternary La-Mg-Ni hydrogen storage alloys withcomposition La3-xMgxNi9 (x = 0.8-1.2) form a new class of the materials for thenegative electrodes in Ni-Metal Hydride (MH) batteries. The electrochemical dischargecapacity of such alloys reaches 400 mAh/g which is 25 % greater than thatof the commercial AB5-type based electrodes, 315 mAh/g. The La3-xMgxNi9alloys crystallize with trigonal PuNi3 type of crystal structure. Magnesium replaceslanthanum to form the hybrid LaNi5 + Laves phase structures and favorablychanges the thermodynamics of the metal-hydrogen interactions allowingimproved performance of the advanced metal hydride battery electrodes.Differences in melting temperatures of lanthanum, nickel and easily evaporatingmagnesium and a complexity of the phase equilibria in the La-Mg-Ni systemcause difficulties in synthesis of the battery electrode alloys with controlled Mgcontent and a desired phase-structural composition.In present work a La2MgNi9 alloy was in focus. Its successful synthesis hasbeen achieved from the alloy melts containing 0-30 % of overstoichiometric Mgas compared to La2MgNi9 by use of Rapid Solidification performed at variousquenching rates, with a copper wheel rotation speed of 3.1, 10.5 and 20.9 m/s.They were analyzed by synchrotron X-ray diffraction (SR XRD) including in situstudies in hydrogen gas performed at Swiss-Norwegian Beam Lines at ESRF,Grenoble, and by Scanning Electron Microscopy (SEM) with electron probemicroanalysis (EPMA). Pressure-Composition-Temperature isotherms, hydrogenabsorption-desorption cycling and measurements of the electrochemical chargedischargeperformances were employed to characterize hydrogenation behaviorsof the studied alloys. These studies showed that the melt spinning of the alloycontaining 30 % weight excess of Mg quenched using wheel spin speed of 400 RPMallowed obtaining the most homogeneous sample with the optimal microstructureand phase-structural composition corresponding to the formation of La2MgNi9with the highest yield.Variations in magnesium content and selection of optimal conditions for the RapidSolidification process provide complementary possibilities in improving propertiesof the studied La-Mg-Ni alloys as hydrogen storage and battery electrodematerials and provide a possibility to upscale production of the battery alloys.This work was performed at Institute for Energy Technology and at Departmentof Materials Science and Engineering, NTNU.

The most active catalyst for oxygen evolution in PEM water electrolysis is ruthenium oxide. Its major drawback as a commercial catalyst is its poor stability. In a mixed oxide with iridium, ruthenium becomes more stable. However, it would be favorable to find a less expensive substitute to iridium. In this work, the dissolution potential and lifetime of mixed oxides containing ruthenium and tantalum are investigated. In order to effectively determine what effects tantalum and particle size have on stability, only a small amount of tantalum is used, and the catalysts are supported by antimony doped tin oxide, ATO. This leads to a very small particle size, and makes it possible to investigate small amounts of catalyst where little new surface is made available during degradation.Catalysts were prepared with the normal polyol method by reducing RuCl3 and TaCl5 in ethylene glycol, EG, before the metal particles were deposited on the ATO support. The catalysts were investigated electrochemically with cyclic and linear voltammetry. Furthermore, the lifetime of four catalysts were determined by chronoamperometry at 1.455V vs. RHE. The compositions and loading of catalyst on the support were determined by energy dispersive x-ray spectroscopy (EDS) and the particle sizes were measured with transmission electron microscopy (TEM).In one synthesis, the reduction time and temperature were increased from 3 hours at 170◦C to 4 hours at 190◦C in order to increase the reduction rate. While this had no effect on the Ta composition, the catalyst got a fraction of amorphous phase not found in any of the other catalysts. The amorphous Ru0.9Ta0.1O2 particles had the largest particle size and the highest stability of the ones investigated. 10wt% water was added to the synthesis of an ATO-RuO2 catalyst in order to increase the particle size, but no significant effect was observed. Larger RuO2 particles and amorphous Ru0.9Ta0.1O2 particles were obtained by collecting them as unsupported catalysts.The addition of tantalum has a negative effect on the catalytic activity. When Ta is present, the dissolution potential of Ru at around 1.45V is slightly increased, but the degradation rate is increased above 1.49V. A large particle size in RuO2 has a significant positive effect on stability.

Alkaline water electrolysis need a catalyst with low overpotential and high current densitiy for oxygen evolution in order to be a commercial viable hydrogen source in the future. Finding and establishing a correlation between electrocatalytic activity and charge carrier density will help towards finding an optimum catalyst for this purpose. Such comparisons have been made using theoretical values for charge carrier density, but the aim of this work is to use charge carrier data from experimental values.Five powders of La<sub>1-x</sub>Sr<sub>x</sub>CoO<sub>3</sub> (with compositions x = 0, 0.25, 0.5, 0.75, 1) were synthesized by solid-state synthesis and sintered to pellets. The pellet surfaces were investigated in alkaline solution (pH = 13) by cyclic voltammetry, polarization and impedance measurements. Polariza- tion curves with Tafel lines and Mott-Schottky plots were established. The powders and pellet surfaces were investigated by XRD, SEM, EDS, AFM and light microscope.The polarization curves revealed a volcanic behavior with an increase in catalytic activity from x = 0 up to x = 0.75 and then decreasing. The charge carrier density increased with increasing strontium doping. The resulting comparison gave figure 34. Surface investigation revealed much porosity. Because of corrosion, the surface area increased with measuring, and finding the real surface area and the roughness proved to be problematic.A volcanic behavior of the charge carrier density and electrocatalytic activity relationship were observed. Finding roughness factor values by measuring double layer capacitance measured by the cyclic voltammetry method and dividing by the nominal capacitance for a flat surface proved to be unsuccessful. Better synthesis and sintering procedures of pellets are needed to increase the density of the samples in order to decrease the roughness and the effect of corrosion.

Optimalization of PLD deposition of YSZ for micr-SOFC electrolyte applications by varying deposition pressure and target-substrate distance.Substrate used was Si-based chips and wafers (large area PLD), and the substrate temperature was held at 600. Dense films were obtained at 20 mTorr.

The main aim of this work was to analyze an impedance model for porous semiconductor electrodes consisting of spherical particles. The model should make it possible to analyze the flatband potential for this type of electrodes. The analysis was conducted by simulating the model in MATLAB®. Cyclic voltammetry and electrochemical impedance spectroscopy was performed on titanium oxide, TiO2 P25, anodized titanium and some iridium tin oxides, Ir(1-x)SnxO2. The aim was to use the experimental data as a reference and compare the simulated data with the experimental results. This could not be done because the recorded data for the oxides were too strongly influenced by the support material. The supports tested in this work were Au, Ti and ITO. The simulations show that the capacitance of the models spherical particle is only weakly dependent on the particles surface potential. This indicates that this one-dimensional version of the model might not be sufficient to analyze the spherical particles. However, another analysis method for investigation of Mott-Schottky behavior for porous electrodes was confirmed by the result for the anodized titanium.

Ceramics with mixed ionic and electronic conductivity are being investigated for oxygen separation from air, intended for the production of syngas. Asymmetric membranes, consisting of a dense membrane co-sintered with a porous support are expected to achieve a high flux of oxygen and at the same time adequate strength. As the porous substrate is mainly intended for strength contribution, it is crucial that the flux of oxygen through the dense membrane is not limited by the flow of air through the porous substrate. An oxygen flux of 10 ml min-1 cm-2 should be achieved at operating temperatures (800-1000 °C) for the substrate to be commercially attractive. A biaxial strength of 34MPa has been obtained by similar porous substrates.Four different strategies for achieving high permeating substrates made by solid state La0.2Sr0.8Fe0.8Ta0.2O3-x have been evaluated. Pressed porous substrates were produced both with and without the use of pore formers. The most promising compositions with respect to porosity and permeability were tape casted and characterized with respect to porosity, permeability and strength.

Coin cells with lithium and graphite electrodes were assembled using different combinations of graphite material and electrolyte. Specifically, three commercially available graphite materials and five electrolyte compositions were studied. The cells were discharge-charge cycled with varying parameters in order to determine the performance of the graphite materials and electrolytes. Particularly, a temperature chamber was employed to cycle some cells at temperatures between 0 and 40°C to find the significance of the electrolyte composition and graphite material on the cell performance at these temperatures. The cycled cells were disassembled and samples from the graphite electrode soaked with electrolyte were prepared for thermal analysis, specifically differential scanning calorimetry (DSC). The thermal stability of the graphite electrodes and the influence from the graphite and electrolyte properties and the cycling parameters were analysed. In order to facilitate the interpretation of the results from discharge-charge cycling at different temperatures, DSC analysis from -80 to +50°C was performed on the pure electrolytes.Confirming previous studies, it was found that both the thermal stability and cycling performance were highly influenced by the properties of a solid electrolyte interphase (SEI), situated between the graphite surface and the electrolyte and formed during cycling. The three graphites were good substrates for stable SEI formation, exhibited by high thermal stability after being cycled at room temperature. After cycling with a temperature program, subjecting the cells to temperatures between 0 and 40°C, the thermal stability was generally reduced. This was attributed to increased SEI formation. The properties of both the electrolyte and graphite influenced the SEI and consequent thermal stability, though in different ways.The cell capacity was considerably reduced upon cycling at lower temperatures, such as 10 and 0°C. The results indicate that the electrolyte properties, particularly the viscosity and resulting conductivity, played the most important role in determining the cell performance. Low viscosity electrolyte components should be utilised, maintaining the electrolyte conductivity even at reduced temperatures. The graphite properties did not influence the cell performance at the temperatures studied. Advice is given on which electrolyte components should be avoided to build Li-ion cells performing acceptably at temperatures from 0 to 40°C.

High purity silicon material in solar cell fabrication constitutes 40% of the total cost for conventional solar cell production. One approach to reduce costs would be to use less of this expensive silicon by making thin film solar cells and use a cheaper substrate as mechanical carrier.In this work the main objective has been to manufacture silicon substrates from powder by hot-pressing. The effect of the sintering parameters has been characterized. A secondary objective was to look at the possibility to achieve larger grains by recrystallization.Samples processed by hot-pressing silicon powder of metallurgical grade with varying temperatures (1200-1375 °C), pressures (30-50 MPa) and sintering time (30-60 min) has been carried out. Halogen lamps were used for heat treatment for specific samples after hot-pressing. Microstructure and porosity were characterized using optical and electronic microscopy. EBSD was used to determine the grain size and grain orientation. The density was determined by Archimedes’ method. Resistivity was measured by a conductive probe.Densities higher than 90 % were obtained at high temperatures and pressures. The time conducted at maximum temperature during hot-pressing was not of vital importance with respect to density.The mean particle size of the powder was determined to ~20 μm, while hot-pressed samples had an average grain size of ~30 μm. The samples showed low resistivity due to high impurities of the silicon powder. High surface porosity was found for the less dense samples. Recrystallization was successfully achieved for the sample hot-pressed at 1350 °C, 30 MPa and 30 min, resulting in elimination of pores and significant grain growth from 31,83 to 56,96 μm.Characterizations of the hot-pressed samples are limited to the methods and techniques described above.

Hydrogen transport membranes have gained interest from industry as an alternative to pressure swing adsorption or cryogenic distillation, and are aimed to reduce cost, equipment size, energy consumption and waste generation. Doped strontium cerate stabilized with zirconium exhibit high proton conductivity and chemical stability and is therefore considered to be a promising material for hydrogen transport membranes.The purpose of the work was to investigate if phase pure strontium cerates, stabilized with zirconium and doped with thulium, ytterbium or yttrium, could be synthesized by the Pechini method, and if the membranes exhibited sufficient density. Determination of optimal calcination and sintering parameters was also important parts in the study.SrCe0.75Zr0.20M0.05O3-d, (M=Tm,Y,Yb) were synthesized via the Pechini method, followed by calcination, pressing of green bodies and sintering of dense membranes. Phase purity of powders and sintered membranes was examined by X-ray diffraction. Surface investigation and microstructure was investigated in a scanning electron microscope. Sintering behavior and thermal expansion coefficients was determined by dilatometry. Phase pure and dense orthorhombic perovskite structured SrCe0.75Zr0.20M0.05O3-d;, (M=Tm,Y,Yb) membranes, were obtained by powder calcination at 1000 C, followed by milling and conventional sintering at 1500-1600 C. SrCe0.75Zr0.20Tm0.05O3-d demonstrated the highest density of 98,6%, when sintered at 1500 C. Sintered membranes had a average grain size in the range from 3,2 – 4,9 um. Ball milling is concluded to be of vital importance to obtain sufficient density in the membranes.The membrane characterization is limited to the methods and techniques described above. Hydrogen flux across the membrane, total conductivity, stability in reducing atmosphere and thorough investigation of thermal properties are recommended for further work.

The main object was to investigate the effect of donors, thermal donors and defects on the lifetime on n-type Czochralsky (Cz) silicon. Cz is a technique for making monocrystals by dipping a monocrystalline seed into the melt, and pulling the ingot up as the melt solidifies. Samples were prepared by sawing, grinding and polishing. Copper decoration and preferential etching was done to reveal the defects. Resistivity measurements were performed to investigate the donor distribution. The lifetime and oxygen concentration was measured.The lifetime may be influenced by donors and traps. Traps may be metallic or non-metallic. Dopants and metal contaminants are usually Scheil distributed, which typically involves a relatively stable distribution in most part of the ingot, and a rapid increase in concentration close to the bottom. Metal contaminants may be introduced from the feedstock, and dopants (either n or p dopants) are added to the melt.Oxygen is dissolved from the crucible. The oxygen concentration typically decreases with increasing length, and is controlled by the rotation speed. This was confirmed by the interstitial oxygen measurements. The oxygen concentration showed no change after heat treatment, but the presence of oxygen in itself may contribute to produce lifetime reducing agents, such as precipitates and thermal donors. Thermal donors were found in the first 18cm of the ingot. Both the resistivity and lifetime measurements was used to calculate estimated lifetimes and donor concentrations, respectively. This estimated values were compared with the measured ones, revealing that the lifetime in the ingot was SRH dominated. Thermal donors were found to have less influence on the lifetime than the trapping. Oxygen precipitations may explain the low lifetime found in the center of the ingot up to about 30cm from the crown. Such precipitations are often gathered in defect bands in the sample. CDI of a Cu decorated sample revealed a pattern of different defect densities, which also showed up at the surface of the sample after preferential etching. An H- or L- band was believed to be situated here, which both consist of small oxygen precipitates. Defects arize as a funktion of the pulling parameters, and a low growth rate was connected to the low lifetime here. Indications of the presence of non-metallic traps were found throughout the ingot. However, oxygen precipitates could not explain the non-metallic traps that was found on the outside of the ingot, and the cause of these is therefore unknown. It is however likely that these traps may be connected to the pullrate/temperature gradient-ratio. Most likely metallic traps were also present. It is uncertain whether the non-metallic or metallic traps were the most important to the lifetime of this ingot, as the relative distribution of the two cannot be decided with certainty from the results in this thesis.Contrasts in CDI and steep curves using PCD measurements vs length plots were believed to be due to the lifetime degrading agent that changes the fastest. Metallic traps and the phosphorous dopant are known to be Scheil distributed, hence they appear transparent for the lifetime measurements in areas where the distribution is stable. Thermal donors and non-metallic traps are thus more likely to create contrast in the top parts of an ingot. However, it is not necessarily the phenomenon that causes the contrast that is the major lifetime degradation contributor.