Pyrite (FeS2) thin films prepared by spray method using FeSO4 and (NH4)2Sx

A simple spray method for the preparation of pyrite (FeS₂) thin films has been studied using FeSO₄ and (NH₄)₂S_x as precursors for Fe and S, respectively. Aqueous solutions of these precursors are sprayed alternately onto a substrate heated up to 120°C. Although Fe–S compounds including pyrite are formed on the substrate by the spraying, sulfurization of deposited films is needed to convert other phases such as FeS or marcasite into pyrite. A single-phase pyrite film is obtained after the sulfurization in a H₂S atmosphere at around 500°C for 30 min. All pyrite films prepared show p-type conduction. They have a carrier concentration (p) in the range 10¹⁶–10²⁰ cm⁻³ and a Hall mobility (μ_H) in the range 200–1 cm²/V s. The best electrical properties (p=7×10¹⁶ cm⁻³, μ_H=210 cm²/V s) for a pyrite film prepared here show the excellence of this method. The use of a lower concentration FeSO₄ solution is found to enhance grain growth of pyrite crystals and also to improve electrical properties of pyrite films.     

La0.84Sr0.16MnO3−δ cathodes impregnated with Bi1.4Er0.6O3 for intermediate-temperature solid oxide fuel cells

La_0.84Sr_0.16MnO_3−δ–Bi_1.4Er_0.6O₃ (LSM–ESB) composite cathodes are fabricated by impregnating LSM electronic conducting matrix with the ion-conducting ESB for intermediate-temperature solid oxide fuel cells (IT-SOFCs). The performance of LSM–ESB cathodes is investigated at temperatures below 750 °C by AC impedance spectroscopy. The ion-impregnation of ESB significantly enhances the electrocatalytic activity of the LSM electrodes for the oxygen reduction reactions, and the ion-impregnated LSM–ESB composite cathodes show excellent performance. At 750 °C, the value of the cathode polarization resistance (R_p) is only 0.11 Ω cm² for an ion-impregnated LSM–ESB cathode, which also shows high stability during a period of 200 h. For the performance testing of single cells, the maximum power density is 0.74 W cm⁻² at 700 °C for a cell with the LSM–ESB cathode. The results demonstrate the ion-impregnated LSM–ESB is one of the promising cathode materials for intermediate-temperature solid oxide fuel cells.     

A poly(R1R2R3)–N/H3PO4 composite membrane for phosphoric acid polymer electrolyte membrane fuel cells

A poly(R₁R₂R₃)–N⁺/H₃PO₄ composite membrane has been developed for use in a polymer electrolyte fuel cell (PEMFC). The quaternized polysulfone (QNPSU) membrane doped with H₃PO₄ showed high proton conductivity (0.12 S cm⁻¹) at 160 °C and gave good performance in a single fuel cell tests. The peak power density with the QNPSU/H₃PO₄ composite membrane (at 150 °C, with dry H₂/O₂) was greater than 0.7 W cm⁻². The effect of the phosphoric acid doping level on fuel cell performances with the QNPSU membrane was investigated. The data show that the QNPSU/H₃PO₄ composite membrane is promising for higher temperature PEMFC applications. The study demonstrated that the poly(R₁R₂R₃)–N⁺/H₃PO₄ composite system produced an effective method to connect phosphoric acid to a non-conducting polymer structure, to produce a promising membrane for phosphoric acid polymer electrolyte membrane fuel cells.     

ZnO-doped BaZr0.85Y0.15O3−δ proton-conducting electrolytes: Characterization and fabrication of thin films

ZnO-doped BaZr_0.85Y_0.15O_3−δ perovskite oxide sintered at 1500 °C has bulk conductivity of the order of 10⁻² S cm⁻¹ above 650 °C, which makes it an attractive proton-conducting electrolyte for intermediate-temperature solid oxide fuel cells. The structure, morphology and electrical conductivity of the electrolyte vary with sintering temperature. Optimal electrochemical performance is achieved when the sintering temperature is about 1500 °C. Cathode-supported electrolyte assemblies were prepared using spin coating technique. Thin film electrolytes were shown to be dense using SEM and EDX analyses.     

Enhanced performance of solid oxide fuel cells with Ni/CeO2 modified La0.75Sr0.25Cr0.5Mn0.5O3−δ anodes

The optimization of electrodes for solid oxide fuel cells (SOFCs) has been achieved via a wet impregnation method. Pure La_0.75Sr_0.25Cr_0.5Mn_0.5O_3−δ (LSCrM) anodes are modified using Ni(NO₃)₂ and/or Ce(NO₃)₃/(Sm,Ce)(NO₃)_x solution. Several yttria-stabilized zirconia (YSZ) electrolyte-supported fuel cells are tested to clarify the contribution of Ni and/or CeO₂ to the cell performance. For the cell using pure-LSCrM anodes, the maximum power density (P_max) at 850 °C is 198 mW cm⁻² when dry H₂ and air are used as the fuel and oxidant, respectively. When H₂ is changed to CH₄, the value of P_max is 32 mW cm⁻². After 8.9 wt.% Ni and 5.8 wt.% CeO₂ are introduced into the LSCrM anode, the cell exhibits increased values of P_max 432, 681, 948 and 1135 mW cm⁻² at 700, 750, 800 and 850 °C, respectively, with dry H₂ as fuel and air as oxidant. When O₂ at 50 mL min⁻¹ is used as the oxidant, the value of P_max increases to 1450 mW cm⁻² at 850 °C. When dry CH₄ is used as fuel and air as oxidant, the values of P_max reach 95, 197, 421 and 645 mW cm⁻² at 750, 800, 850 and 900 °C, respectively. The introduction of Ni greatly improves the performance of the LSCrM anode but does not cause any carbon deposit.     

A potential interconnect material for solid oxide fuel cells: Nd0.75Ca0.25Cr0.98O3−δ

Chromium-deficient Nd_0.75Ca_0.25Cr_1−xO_3−δ (0.02 ≤ x ≤ 0.06) oxides are synthesized and assessed as a novel ceramic interconnect for solid oxide fuel cells (SOFCs). At room temperature, all the samples present single perovskite phase after sintering at 1600 °C for 10 h in air. Cr-deficiency significantly improves the electrical conductivity of Nd_0.75Ca_0.25Cr_1−xO_3−δ oxides. No structural transformation occurs in the Nd_0.75Ca_0.25Cr_1−xO_3−δ oxides in the temperature range studied. Among all the samples, the Nd_0.75Ca_0.25Cr_0.98O_3−δ sample with a relative density of 96.3% exhibits the best electrical conductivity of 39.0 and 1.6 S cm⁻¹ at 850 °C in air and hydrogen, respectively. The thermal expansion coefficient of Nd_0.75Ca_0.25Cr_0.98O_3−δ sample is 9.29 × 10⁻⁶ K⁻¹ in the temperature range from 30 to 1000 °C in air, which is close to that of 8 mol% yttria stabilized zirconia electrolyte (10.3 × 10⁻⁶ K⁻¹) and other cell components. The results indicate that Nd_0.75Ca_0.25Cr_0.98O_3−δ is a potential interconnect material for SOFCs.     

Preparation of dense and uniform La0.6Sr0.4Co0.2Fe0.8O3−δ (LSCF) films for fundamental studies of SOFC cathodes

Thin films of La_0.6Sr_0.4Co_0.2Fe_0.8O_3−δ (LSCF) were deposited on (1 0 0) silicon and on GDC electrolyte substrates by rf-magnetron sputtering using a single-phase oxide target of LSCF. The conditions for sputtering were systematically studied to get dense and uniform films, including substrate temperature (23–600 °C) background pressure (1.2 × 10⁻² to 3.0 × 10⁻² mbar), power, and deposition time. Results indicate that to produce a dense, uniform, and crack-free LSCF film, the best substrate temperature is 23 °C and the argon pressure is 2.5 × 10⁻² mbar. Further, the electrochemical properties of a dense LSCF film were also determined in a cell consisting of a dense LSCF film (as working electrode), a GDC electrolyte membrane, and a porous LSCF counter electrode. Successful fabrication of high quality (dense and uniform) LSCF films with control of thickness, morphology, and crystallinity is vital to fundamental studies of cathode materials for solid oxide fuel cells.     

Electrical properties of Mg-doped Gd0.1Ce0.9O1.95 under different sintering conditions

Ce_0.9Gd_0.1O_1.95 with various Mg doping contents was synthesized by citric acid-nitrate low temperature combustion process and sintered under different conditions. The crystal structures, microstructures and electrical properties were characterized by X-ray diffraction (XRD), field-emission scanning electron microscopy (FESEM) and ac impedance spectroscopy. Low solubility of Mg²⁺ in Ce_0.9Gd_0.1O_1.95 lattice was evidenced by XRD and FESEM micrographs. The samples sintered at 1300 °C exhibited the higher total conductivity than those sintered at 1100 and 1500 °C, with the maximum value of 1.48 × 10⁻² S cm⁻¹ (measured at 600 °C) at the Mg doping content of 6 mol%, corresponding to the minimum total activation energy (E_tol) of 0.84 eV (150–400 °C). The effect of Mg doping on the electrical conductivity was significant particularly at higher sintering temperatures. At the sintering temperature of 1500 °C, the addition of Mg (10 mol%) enhanced the grain boundary conductivity by over 10² times comparing with that of undoped Ce_0.9Gd_0.1O_1.95, which may be explained by the optimization of space charge layer due to the segregation of Mg²⁺ to the grain boundaries.     

Characterization of Pr1−xSrxCo0.8Fe0.2O3−δ (0.2 ≤ x ≤ 0.6) cathode materials for intermediate-temperature solid oxide fuel cells

Cathode materials consisting of Pr_1−xSr_xCo_0.8Fe_0.2O_3−δ (x = 0.2–0.6) were prepared by the sol–gel process for intermediate-temperature solid oxide fuel cells (IT-SOFCs). The samples had an orthorhombic perovskite structure. The electrical conductivities were all higher than 279 S cm⁻¹. The highest conductivity, 1040 S cm⁻¹, was found at 300 °C for the composition x = 0.4. Symmetrical cathodes made of Pr_0.6Sr_0.4Co_0.8Fe_0.2O_3−δ (PSCF)–Ce_0.85Gd_0.15O_1.925 (50:50 by weight) composite powders were screen-printed on GDC electrolyte pellets. The area specific resistance value for the PSCF–GDC cathode was as low as 0.046 Ω cm² at 800 °C. The maximum power densities of a cell using the PSCF–GDC cathode were 520 mW cm⁻², 435 mW cm⁻² and 303 mW cm⁻² at 800 °C, 750 °C and 700 °C, respectively.     

Characterization of the 75% Gd0.8Sr0.2CoO3−δ/25% Ce0.9Gd0.1O2−δ composite cathode system for use in intermediate temperature solid oxide fuel cells

The composite cathode system is examined for suitability on a Ce_0.9Gd_0.1O_2−δ electrolyte based solid oxide fuel cell at intermediate temperatures (500–700 °C). The cathode is characterized for electronic conductivity and area specific charge transfer resistance. This cathode system is chosen for its excellent thermal expansion match to the electrolyte, its relatively high conductivity (115 S cm⁻¹ at 700 °C), and its low activation energy for oxygen reduction (99 kJ mol⁻¹). It is found that the decrease of sintering temperature of the composite cathode system produces a significant decrease in charge transfer resistances to as low as 0.25 Ω cm². The conductivity of the cathode systems is between 40 and 88 S cm⁻¹ for open porosities of 30–40%.     

Multi Fermi level pinning at metal/Cu(InGa)(SeS)2 interfaces

Metal contacts to chemically etched Cu(InGa)(SeS)₂ layers have been investigated using current–voltage and capacitance–voltage techniques. Oxidising chemicals enhance the Fermi level pinning at metal/Cu(InGa)(SeS)₂ interfaces. The formation of a Schottky barrier at metal/p-Cu(InGa)(SeS)₂ interface is dominated by Fermi level pinning at one of the four levels, 0.77±0.02, 0.84±0.02, 0.93±0.02 and 1.03±0.02 eV above the valence band maximum. These observed levels determined from current–voltage measurements show a good agreement with some of the previously published photoluminescence, deep level transient spectroscopy and photo acoustic spectroscopy observations. The capacitance–voltage measurements showed that this material has near ideal doping concentration of 1.0×10¹⁶ cm⁻³ for fabricating solar cell devices.     

The structural characterization of (NH4)2B10H10 and thermal decomposition studies of (NH4)2B10H10 and (NH4)2B12H12

The structure of (NH₄)₂B₁₀H₁₀ (1) was determined through powder XRD analysis. The thermal decomposition of 1 and (NH₄)₂B₁₂H₁₂ (2) was examined between 20 and 1000 °C using STMBMS methods. Between 200 and 400 °C a mixture of NH₃ and H₂ evolves from both compounds; above 400 °C only H₂ evolves. The dihydrogen bonding interaction in 1 is much stronger than that in 2. The stronger dihydrogen bond in 1 resulted in a significant reduction by up to 60 °C, but with a corresponding 25% decrease in the yield of H₂ in the lower temperature region and a doubling of the yield of NH₃. The decomposition of 1 follows a lower temperature exothermic reaction pathway that yields substantially more NH₃ than the higher temperature endothermic pathway of 2. Heating of 1 at 250 °C resulted in partial conversion of B₁₀H₁₀²⁻ to B₁₂H₁₂²⁻. Both 1 and 2 form an insoluble polymeric material after decomposition. The elements of the reaction network that control the release of H₂ from the B₁₀H₁₀²⁻ can be altered by conducting the experiment under conditions in which pressures of NH₃ and H₂ are either near, or away from, their equilibrium values.     

Thermal cycle stability of BaO–B2O3–SiO2 sealing glass

Thermal cycle stability is very important for glass seals in planar solid oxide fuel cell (pSOFC) applications. In the present study, thermal cycle stability of a thermally stable sealing glass is investigated using a sealing fixture from 150 °C to 700 °C. SS410 alloy with the TEC (thermal expansion coefficient) of 12.2 × 10⁻⁶ K⁻¹ (room temperature to 700 °C) is used to evaluate the effect of TEC mismatch on the thermal cycle stability. The leak rates increase with thermal cycles and appear to be two different stages. Microstructure examinations are performed to investigate the degradation mechanism of the thermal cycle stability. It is found that the sealing glass interacts chemically with the SS410 alloy and the formation of BaCrO₄ new phase results in the rapid increase of the leak rates.     

Structural, thermal and electrochemical properties of layered perovskite SmBaCo2O5+d, a potential cathode material for intermediate-temperature solid oxide fuel cells

The synthesis, conductivity properties, area specific resistance (ASR) and thermal expansion behaviour of the layered perovskite SmBaCo₂O_5+d (SBCO) are investigated for use as a cathode material for intermediate-temperature solid oxide fuel cells (IT-SOFCs). The SBCO is prepared and shows the expected orthorhombic pattern. The electrical conductivity of SBCO exhibits a metal–insulator transition at about 200 °C. The maximum conductivity is 570 S cm⁻¹ at 200 °C and its value is higher than 170 S cm⁻¹ over the whole temperature range investigated. Under variable oxygen partial pressure SBCO is found to be a p-type conductor. The ASR of a composite cathode (50 wt% SBCO and 50 wt% Ce_0.9Gd_0.1O_2−d, SBCO:50) on a Ce_0.9Gd_0.1O_2−d (CGO91) electrolyte is 0.05 Ω cm² at 700 °C. An abrupt increase in thermal expansion is observed in the vicinity of 320 °C and is ascribed to the generation of oxygen vacancies. The coefficients of thermal expansion (CTE) of SBCO is 19.7 and 20.0 × 10⁻⁶ K⁻¹ at 600 and 700 °C, respectively. By contrast, CTE values for SBCO:50 are 12.3, 12.5 and 12.7 × 10⁻⁶ K⁻¹ at 500, 600 and 700 °C, that is, very similar to the value of the CGO91 electrolyte.     

Stable, easily sintered BaCe0.5Zr0.3Y0.16Zn0.04O3−δ electrolyte-based protonic ceramic membrane fuel cells with Ba0.5Sr0.5Zn0.2Fe0.8O3−δ perovskite cathode

A stable, easily sintered perovskite oxide BaCe_0.5Zr_0.3Y_0.16Zn_0.04O_3−δ (BCZYZn) as an electrolyte for protonic ceramic membrane fuel cells (PCMFCs) with Ba_0.5Sr_0.5Zn_0.2Fe_0.8O_3−δ (BSZF) perovskite cathode was investigated. The BCZYZn perovskite electrolyte synthesized by a modified Pechini method exhibited higher sinterability and reached 97.4% relative density at 1200 °C for 5 h in air, which is about 200 °C lower than that without Zn dopant. By fabricating thin membrane BCZYZn electrolyte (about 30 μm in thickness) on NiO–BCZYZn anode support, PCMFCs were assembled and tested by selecting stable BSZF perovskite cathode. An open-circuit potential of 1.00 V, a maximum power density of 236 mW cm⁻², and a low polarization resistance of the electrodes of 0.17 Ω cm² were achieved at 700 °C. This investigation indicated that proton conducting electrolyte BCZYZn with BSZF perovskite cathode is a promising material system for the next generation solid oxide fuel cells.     

Some physical investigations on AgInS2 sprayed thin films

AgInS₂ thin films have been prepared on glass substrates by the spray pyrolysis process using an aqueous solution which contains silver acetate (AgCH₃CO₂), thiourea (SC(NH₂)₂) and indium chloride (InCl₃) as precursors. The depositions were carried out in the range of the substrate temperature from 260 to 420 °C. The value of the concentration ratio in the spray solution of indium and silver elements x=[Ag⁺]/[In³⁺] was varied from 1 to 1.5 with [In³⁺]=10⁻² M and [S²⁻]/[In³⁺] was taken constant, equal to 4. The structural study shows that AgInS₂ thin film, prepared at 420 °C using optimal concentration ratio x=1.3 crystallizes in the chalcopyrite phase with a strong (1 1 2) X-ray diffraction line. Moreover, microprobe analysis (EPMA) shows that a nearly stoichiometric composition is obtained for these experimental conditions. Indeed, the atomic percentage of elements were. 24.5, 25.0, 49.5 for Ag, In and S, respectively. On the other hand from transmission and reflectance spectra, the obtained band gap energy is 1.83 eV for such film.     

The obstructed diffusion of the I3 ion in mesoscopic TiO2 membranes

The diffusional permeability of I⁻₃ ion in acetonitrile in free standing TiO₂ membrane with a porosity of 55% was examined. The apparent diffusion coefficient, D_app at 25°C of the ion was found to be 3.4×10⁻⁶ cm^{2 −1}, an order of magnitude smaller than the free diffusion at the same temperature. The temperature dependency of D_app was measured in the range 0–30°C and analysed in terms of the Walden product. The diffusional activation energy was found to be 13.5 kJ/mol. The parameters of interest for the efficiency of mesoscopic wet solar cells are discussed. A back of an envelope calculation shows that although the obstructed diffusion coefficient of the I⁻₃ ion was an order of magnitude smaller than the free diffusion the diffusional flux is still sufficient to meet a current density of 50 mA cm⁻². At incident photon flux of 1 kW m⁻² and at a photopotential of 0.6 V this would correspond to a solar energy efficiency of approximately 30%.     

Bulk p-CuInSe2 photo-electrochemical solar cells

Dense CuInSe₂ of high quality, prepared by the fusion technique in evacuated quartz ampoule from stoichiometric melt, crystallizes in the chalcopyrite structure. Compositional analysis carried out by secondary ion mass spectrometry (SIMS) and energy dispersive spectroscopy (EDS) indicates a uniform distribution of elements through the depth and a composition close to the stoichiometry. The diffuse reflectance spectrum gives a band gap at 0.94 eV. The electrical conductivity follows an Arrhenius-type law with activation energy of 23 meV in conformity with polarons hopping. Above 320 °C, CuInSe₂ undergoes an irreversible oxidation. The thermal variation of the thermopower indicates p-type behavior attributed to copper deficiency and a hole mobility μ_300 K of 0.133 cm² V⁻¹ s⁻¹, thermally activated. In KCl media, the compound exhibits an excellent chemical stability with a corrosion rate of 8 μmol cm⁻² month⁻¹. The photo-electrochemical properties, investigated for the first time on the ingots, confirm the p-type conductivity. From the capacitance measurements, the flat band potential (V_fb=−0.62V_SCE) and the holes density (N_A=4×10¹⁷ cm⁻³) were determined. The valence band, located at 4.43 eV below vacuum, is made up of mainly Se orbital with little admixture of Cu character. The change of the electrolyte causes a variation in the potential V_fb (dV_fb/dpH=−0.058 V pH⁻¹) indicating strong OH⁻ adsorption. The fill factor in S²⁻ media was found to be 0.54; such result was corroborated by semi-logarithmic plots.     

Synthesis of LiFePO4/polyacenes using iron oxyhydroxide as an iron source

LiFePO₄/polyacenes (PAS) composite is synthesized by iron oxyhydroxide as a new raw material and phenol–formaldehyde resin as both reducing agent and carbon source. The mechanism of the reaction is outlined by the analysis of XRD, FTIR as well as TG/DSC. The results show that the formation of LiFePO₄ is started at 300 °C, and above 550 °C, the product can be mainly ascribed to olivine LiFePO₄. The electrochemical properties of the synthesized composites are investigated by charge–discharge tests. It is found that the prepared sample at 750 °C (S750) has a better electrochemical performance than samples prepared at other temperatures. A discharge capacity of 158 mAh g⁻¹ is delivered at 0.2 C. Under high discharge rate of 10 C, a discharge capacity of 145 mAh g⁻¹ and good capacity retention of 93% after 800 cycles are achieved. The morphology of S750 and PAS distribution in it are investigated by SEM and TEM.     

Energy efficient simultaneous oxidative conversion and thermal cracking of ethane to ethylene using supported BaO/La2O3 catalyst in the presence of limited O2

An energy efficient conversion of ethane to ethylene involving simultaneous oxidative conversion (which is exothermic) and thermal cracking (which is endothermic) reactions of ethane in the presence of steam (steam/C₂H₆ mol RATIO=1.0) and limited O₂ (C₂H₆/O₂ mol ratio 4.0) over a BaO-promoted La₂O₃ supported on low surface area macroporous silica-alumina commercial catalyst carrier has been thoroughly investigated. Influence of various process parameters such as temperature (700–850°C), C₂H₆/O₂ feed ratio (4.0–8.0) and space velocity (50,000–200,000 cm³ g⁻¹ h⁻¹) on the conversion, product selectivity and net heat of reactions in the process has also been studied. At all the process conditions, there was no coke deposition on the catalyst. High selectivity ( 85%) for C₂₊ olefins (at 50–60% conversion) can be obtained in the process at a low contact time (<10 ms), particularly for the higher C₂H₆/O₂ ratios ( 6.0) and temperatures ( 800°C). The process exothermicity is decreased appreciably with increasing the temperature and/ or the C₂H₆/O₂ ratio. The net heat of reaction in the process can be controlled by manipulating the C₂H₆/O₂ ratio and reaction temperature. Also, because of simultaneously occurring endothermic and exothermic reactions, the process is highly energy efficient and non-hazardous.