Optical and photoelectrical properties of β-In2S3 thin films prepared by two-stage process

β-In₂S₃ films were grown on glass as well as on quartz substrates by rapid heating of metallic indium films in H₂S atmosphere. The effect of sulfurization temperature and time on the growth, structural, electrical and photoelectrical properties of β-In₂S₃ films has been investigated. Highly oriented single-phase β-In₂S₃ films were grown by the sulfurization technique. The morphology and composition of films have been characterized. The optical band gap of β-In₂S₃ is found to vary from 1.9 to 2.5 eV when the sulfurization temperature is varied from 300 to 600 °C or by increasing the sulfurization time. The electrical properties of the thin films have also been studied; they have n-type electrical conductivity. The photoelectrical properties of the β-In₂S₃ films are also found to depend on the sulfurizing temperature. A high photoresponse is obtained for films prepared at a sulfurizing temperature of 600 °C. β-In₂S₃ can be used as an alternative to toxic CdS as a window layer in photovoltaic technology.     

Preparation of In2O3:F thin films grown by spray pyrolysis technique

Transparent conducting fluorine doped indium oxide (In₂O₃:F) thin films have been deposited on Corning 7059 glass substrates by the spray pyrolysis technique. The structural, electrical, and optical properties of these films were investigated as a function of substrate temperature. The X-ray diffraction pattern of the films deposited at lower substrate temperature (T_s=300 °C) showed no peaks of In₂O₃:F. In the useful range for deposition (i.e. 425–600 °C), the orientation of the films was predominantly [400]. For the 4500 Å thick In₂O₃:F deposited with an F content of 10-wt%, the minimum sheet resistance was 120 Ω and average transmission in the visible wavelength rang (400–700 nm) was 88%.     

Morphological, optical and photocatalytic properties of TiO2–Fe2O3 multilayers

Morphological, optical and photocatalytic properties of TiO₂, Fe₂O₃ and TiO₂–Fe₂O₃ samples (formed by 1, 3 and 5 coatings) were studied. The layers were deposited on glass substrate by the sol–gel method. The catalytic activity of the samples was studied by the photodecomposition of methylene blue (MB) under visible light illumination. The FTIR results indicate that all samples present surface OH radicals that are bound either to the Ti or Fe atoms. This effect is better visualized at larger number of coatings in the TiO₂–Fe₂O₃/glass systems. Also, two mechanisms are observed during the photodecomposition of the MB.     

Study of electron-beam evaporated Sn-doped In2O3 films

Electron beam evaporated Sn-doped In₂O₃ films have been prepared from the starting material with composition of (1 − x) In₂O₃ − -x SnO₂, where x = 0.0, 0.010, 0.025, 0.050, 0.090, and 0.120. X-ray photoelectron spectroscopy, Rutherford backscattering spectrometry, and X-ray diffraction analysis were carried out on the films. Luminous transmittance and electrical resistivity of the films, show weak dependence on x. The composition of the film ([Sn]/[In] atomic ratio) was found to differ from that of the starting material. In fact, the atomic ratio was higher in the film than in the starting material by a factor which increases with x (ranging from 1.0 to 2.6). There is a relatively broad resistivity minimum in the layer atomic ratio range Sn/In = 0.06 − -0.09. These results compare well with those reported in the literature for Sn-doped In₂O₃ films, prepared by pyrolitic (spray) method.     

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.     

Photocurrent enhancement of wide bandgap Bi2O3 by Bi2S3 over layers

Sintered Bi₂O₃ pellets exhibited insulating properties at room temperature. Partial reduction of sintered Bi₂O₃ pellets increased the conductivity. Reduced Bi₂O₃ pellets exhibited n-type semiconductor properties. Microcrystals of Bi₂S₃ were formed on sintered Bi₂O₃ pellets by sulfurizing them in H₂S atmosphere. The direct band-gap and indirect band-gap of Bi₂S₃ were evaluated as 1.2 and 0.4 eV, respectively. A high incident photon to current conversion efficiency in the near IR region was observed on Bi₂S₃|Bi₂O₃ electrodes. Photocurrent generation of Bi₂S₃|Bi₂O₃ electrodes was explained from the viewpoint of semiconductor sensitization. The flat band potential of Bi₂S₃ was evaluated as −1.1 V vs. Ag|AgCl in aqueous polysulfide redox electrolyte (1 M OH⁻, 1 M S²⁻, 10⁻² M S).     

Synthesis and assessment of La0.8Sr0.2ScyMn1−yO3−δ as cathodes for solid-oxide fuel cells on scandium-stabilized zirconia electrolyte

Perovskite-type La_0.8Sr_0.2Sc_yMn_1−yO_3−δ oxides (LSSMy, y = 0.0–0.2) were synthesized and investigated as cathodes for solid-oxide fuel cells (SOFCs) containing a stabilized zirconia electrolyte. The introduction of Sc³⁺ into the B-site of La_0.8Sr_0.2MnO_3−δ (LSM) led to a decrease in the oxides’ thermal expansion coefficients and electrical conductivities. Among the various LSSMy oxides tested, LSSM0.05 possessed the smallest area-specific cathodic polarization resistance, as a result of the suppressive effect of Sc³⁺ on surface SrO segregation and the optimization of the concentration of surface oxygen vacancies. At 850 °C, it was only 0.094 Ω cm² after a current passage of 400 mA cm⁻² for 30 min, significantly lower than that of LSM (0.25 Ω cm²). An anode-supported cell with a LSSM0.05 cathode demonstrated a peak power density of 1300 mW cm⁻² at 850 °C. The corresponding value for the cell with LSM cathode was 450 mW cm⁻² under the same conditions. The LSSM0.05 oxide may potentially be a good cathode material for IT-SOFCs containing doped zirconia electrolytes.     

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.     

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.     

Photoelectrochemical behavior of In2S3 formed on sintered In2O3 pellets

Microcrystals of In₂S₃ were formed on sintered In₂O₃ pellets by sulfurizing in H₂S atmosphere. The flat band potential of compound In₂S₃|In₂O₃ electrodes was evaluated as −1.0 V vs Ag|AgCl in 1 M KOH, 1 M Na₂S, 10⁻² M S. Significantly enhanced photocurrent was observed on compound In₂S₃|In₂O₃ electrodes with a lower degree of sulfurization to that of compound In₂S₃|In₂O₃ electrodes with higher degree of sulfurization. Photocurrent generation of compound In₂S₃|In₂O₃ electrodes was explained from the viewpoint of semiconductor sensitization.     

Carbon-doped Sb2S3 thin films: Structural, optical and electrical properties

We report the modification of electrical properties of chemical-bath-deposited antimony sulphide (Sb₂S₃) thin films by thermal diffusion of carbon. Sb₂S₃ thin films were obtained from a chemical bath containing SbCl₃ and Na₂S₂O₃ salts at room temperature (27 °C) on glass substrates. A carbon thin film was deposited on Sb₂S₃ film by arc vacuum evaporation and the Sb₂S₃-C layer was subjected to heating at 300 °C in nitrogen atmosphere or in low vacuum for 30 min. The value of resistivity of Sb₂S₃ thin films was substantially reduced from 10⁸ Ω cm for undoped condition to 10² Ω cm for doped thin films. The doped films, Sb₂S₃:C, retained the orthogonal stibnite structure and the optical band gap energy in comparison with that of undoped Sb₂S₃ thin films. By varying the carbon content (wt%) the electrical resistivity of Sb₂S₃ can be controlled in order to make it suitable for various opto-electronic applications.     

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.     

Effect of TiO2-coating on the electrochemical performances of LiCo1/3Ni1/3Mn1/3O2

A novel method to improve the cycling performance of LiCo_1/3Ni_1/3Mn_1/3O₂ in lithium-ion batteries by TiO₂-coating with an in situ dipping and hydrolyzing method was presented in this work. The microstructure of the TiO₂-coated LiCo_1/3Ni_1/3Mn_1/3O₂ was characterized by XRD, SEM and TEM, and their electrochemical performances were evaluated by EIS and galvonostatic charge-discharge test. SEM and TEM images show that the TiO₂ are pasted on the surface of the LiCo_1/3Ni_1/3Mn_1/3O₂ with nano-size. The XRD patterns indicate that the crystal structure of the TiO₂-coated LiCo_1/3Ni_1/3Mn_1/3O₂ shows no obvious change compares with the bare material. The TiO₂-coated LiCo_1/3Ni_1/3Mn_1/3O₂ possesses improved cycle performance and rate capability. The capacity retention of 1.0 wt.% TiO₂-coated material is more than 99.0% after 12 cycles at 3.0 C while that of the bare sample is only 86.6%. The capacity of coated material at 5.0 C remains 66.0% of the capacity at 0.2 C, while that of the bare LiCo_1/3Ni_1/3Mn_1/3O₂ is only 31.5%.     

Optical properties of sol–gel deposited Al2O3 films

Highly transparent, uniform and corrosion resistant Al₂O₃ films were prepared on stainless-steel and quartz substrates by the sol–gel process from stable coating solutions using aluminum-sec-butoxide, Al(OBu^s)₃ as precursor, acetylacetone, AcAcH as chelating agent and nitric acid, HNO₃, as catalyzer. Films up to 1000 nm thick were prepared by multiple spin coating deposition, and were characterized by X-ray diffractometry (XRD), X-ray photoelectron spectroscopy (XPS), scanning electron microscopy (SEM), thermogravimetric analysis (TGA), differential scanning calorimetry (DSC), Fourier transform infrared spectroscopy (FTIR), optical spectroscopy and micro Vickers hardness test. XRD of the film heat treated at 400°C showed that they had an amorphous structure. XPS confirmed that they were stoichiometric Al₂O₃. The refractive index (n) and extinction coefficient (k) were found to be n=1.56±0.01 and k=0.003±0.0002 at 600 nm, respectively. The surface microhardness and corrosion resistance investigations showed that Al₂O₃ films improved the surface properties of stainless-steel substrates.     

Stability of Y2O3 hydrogen isotope permeation barriers in hydrogen at high temperatures

Hydrogen isotope permeation barriers (HIPB) have great potential applications in the fields of hydrogen energy and thermonuclear fusion energy. Here, we report the stability of Y₂O₃ HIPB in gaseous hydrogen at high temperatures including the structures, mechanical properties and electrical properties. With increasing hydrogen treatment time at 700 °C, the high-index diffractions of Y₂O₃ became weak gradually whereas the (400) diffraction was strengthened. The color of the Y₂O₃ HIPB changed from brown to gray. The bonding strength decreased by 61% with increasing hydrogen treatment time, and finally remained unchanged. Meanwhile, the electrical resistivity of the Y₂O₃ HIPB decreased from 8.2 × 10⁹ Ω cm by over two orders of magnitude and then tended to be constant. The oxygen loss as well as hydrogen incorporation was proposed to be responsible for these modifications and indications of the present work for preparation of HIPB with high reliability were discussed.     

Cycle life improvement of ZrO2-coated spherical LiNi1/3Co1/3Mn1/3O2 cathode material for lithium ion batteries

A modified synthesis process was developed based on co-precipitation method followed by spray drying process. In this process, a spherical shaped (Co_1/3Ni_1/3Mn_1/3)(OH)₂ precursor was synthesized by co-precipitation and pre-heated at 500 °C to form a high structural stability spinel (CoNiMn)O₄ to maintain its shape for further processing. The spherical LiNi_1/3Co_1/3Mn_1/3O₂ was then prepared by spray drying process using spherical spinel (CoNiMn)O₄. LiNi_1/3Co_1/3Mn_1/3O₂ powders were then modified by coating their surface with a uniform and nano-sized layer of ZrO₂. The ZrO₂-coated LiNi_1/3Co_1/3Mn_1/3O₂ material exhibited an improved rate capability and cycling stability under a high cut-off voltage of 4.5 V. X-ray diffraction (XRD) measurements revealed that the material had a well-ordered layered structure and Zr was not doped into the LiNi_1/3Co_1/3Mn_1/3O₂. Electrochemical impedance spectroscopy measurements showed that the coated material has stable cell resistance regardless of cycle number. The interrupt charging/discharging test indicated that the ZrO₂ coating can suppress the polarization effects during the charging and discharging process. From these results, it is believed that the improved cycling performance of ZrO₂-coated LiNi_1/3Co_1/3Mn_1/3O₂ is attributed to the ability of ZrO₂ layer in preventing direct contact of the active material with the electrolyte resulting in a decrease of electrolyte decomposition reactions.     

Visible light-induced hydrogen over CuFeO2 via S2O3 oxidation

The properties of CuFeO₂ have been studied according to the catalytic hydrogen production upon visible light. CuFeO₂ with a low band gap E_g, a good chemical stability and a suitable flat band potential appears as a suitable candidate. The potential of photoelectrons allows favorably a thermodynamically H₂-evolution from alkaline thiosulfate S₂O₃²⁻ solution. There is a major difference between pure and loaded oxide with some metal catalysts. Our best results have been obtained with unloaded CuFeO₂ at 50 °C and pH 13.60. Thiosulfate S₂O₃²⁻ ions can be oxidized to sulfite SO₃²⁻ and subsequently to sulfate SO₄²⁻ and the electronic exchange occurs via mediation of surface states. The quite high H₂-formation at the beginning shows a tendency towards saturation, it competes with SO₃²⁻ produced by parallel oxidation of S₂O₃²⁻.     

New trends to grow the n-CdZn (S1−xSex)2/p-CuIn(S1−xSex)2 heterojunction thin films for solar cell applications

The n-CdZn(S_1−xSe_x) and p-CuIn(S_1−xSe_x)₂ thin films have been grown by the solution growth technique (SGT) on glass substrates. Also the heterojunction (p–n) based on n-CdZn (S_1−xSe_x)₂ and p-CuIn (S_1−xSe_x)₂ thin films fabricated by same technique. The n-CdZn(S_1−xSe_x)₂ thin film has been used as a window material which reduced the lattice mismatch problem at the junction with CuIn (S_1−xSe_x)₂ thin film as an absorber layer for stable solar cell preparation. Elemental analysis of the n-CdZn (S_1−xSe_x)₂ and p-CuIn(S_1−xSe_x)₂ thin films was confirmed by energy-dispersive analysis of X-ray (EDAX). The structural and optical properties were changed with respect to composition ‘x’ values. The best results of these parameters were obtained at x=0.5 composition. The uniform morphology of each film as well as the continuous smooth thickness deposition onto the glass substrates was confirmed by SEM study. The optical band gaps were determined from transmittance spectra in the range of 350–1000 nm. These values are 1.22 and 2.39 eV for CuIn(S_0.5Se_0.5)₂ and CdZn(S_0.5Se_0.5)₂ thin films, respectively. J–V characteristic was measured for the n-CdZn(S_1−xSe_x)₂/p-CuIn(S_1−xSe_x)₂ heterojunction thin films under light illumination. The device parameters V_oc=474.4 mV, J_sc=13.21 mA/cm², FF=47.8% and η=3.5% under an illumination of 85 mW/cm² on a cell active area of 1 cm² have been calculated for solar cell fabrication. The J–V characteristic of the device under dark condition was also studied and the ideality factor was calculated which is equal to 1.9 for n-CdZn(S_0.5Se_0.5)₂/p-CuIn(S_0.5Se_0.5)₂ heterojunction thin films.     

Evaluation of Ni/Y2O3/Al2O3 catalysts for hydrogen production by autothermal reforming of methane

Ni/xY₂O₃–Al₂O₃ (x = 5, 10, 15, 20 wt%) catalysts were prepared by sequential impregnation synthesis. The catalytic performance for the autothermal reforming of methane was evaluated and compared with Ni/γ-Al₂O₃ catalyst. The physicochemical properties of catalysts were characterized by X-ray diffraction (XRD), Transmission electron microscope (TEM), X-Ray Photoelectron Spectrometer (XPS), Thermo Gravimetric Analyzer (TGA) and H₂-temperature programmed reduction techniques (TPR). The decrease of nickel particle size and the change of reducibility were found with Y modification. The CH₄ conversion increased with elevating levels of Y₂O₃ from 5% to 10%, then decreased with Y content from 10% to 20%. Ni/xY₂O₃–Al₂O₃ catalysts maintained high activity after 24 h on stream, while Ni/Al₂O₃ had a significant deactivation. The characterization of spent catalysts indicated that the addition of Y retarded Ni sintering and decreased the amount of coke.     

WO3−x nanowires based electrochromic devices

A simple method was developed to fabricate tungsten oxide (WO_3−x) nanowires based electrochromic devices. The WO_3−x nanowires are grown directly from tungsten oxide powders in a tube furnace. The WO_3−x nanowires have diameters ranging from 30 to 70 nm and lengths up to several micrometers. The WO_3−x nanowires based device has short bleach-coloration transition time and can be grown on a large scale directly onto an ITO-coated glass that makes it potential in many electrochromic applications. The structure, morphology, and composition of the WO_3−x nanowires were characterized using the scanning electron microscopy, transmission electron microscopy, X-ray diffraction, and energy-dispersive spectrometer. The optical and electrochromic performance of the nanowires layer under lithium intercalation was studied in detail by UV–VIS–NIR spectroscope and cyclic voltameter.