Porous indium oxide thin films deposited by electrostatic spray deposition technique

This paper presents the preparation process of porous indium oxide (In₂O₃) films using a novel deposition technique, i.e., electrostatic spray deposition (ESD). The films were deposited on platinum-coated alumina substrates using as precursor solution indium chloride in ethanol and acetic acid. The films were characterized using scanning electron microscopy (SEM), X-ray diffraction (XRD), transmission electron microscopy (TEM) and Raman spectroscopy. The nanocrystalline structure of the films was evidenced by TEM and also by XRD studies. The Raman spectroscopy and XRD measurements revealed the cubic phase of In₂O₃ films. Considering the obtained results, we conclude that the ESD technique is an efficient, cheap and successful method for the preparation of porous indium oxide films.     

Rapid deposition of YBCO films by laser CVD and effect of lattice mismatch on their epitaxial growth and critical temperature

a-Axis- and c-axis-oriented YBa₂Cu₃O_7–δ (YBCO) films were grown on (100) SrTiO₃ substrate by laser chemical vapour deposition (laser CVD). The effect of lattice mismatch between films and substrates on in-plane and out-of-plane crystallinity and critical temperature (T_C) was investigated. The preferred orientation changed from a-axis to c-axis as the deposition temperature increased from 928 to 1049 K. The c-axis-oriented YBCO showed a minimum of full width at half maximum of 0.5° for the ω-scan and 1.0° for the φ-scan. A smaller mismatch between YBCO films and substrates led a higher crystallinity for in-plane and out-of-plane epitaxial growths. A high T_C of 90 K was obtained for the c-axis-oriented YBCO films. The deposition rate of the YBCO films was 58–101 μm h⁻¹, approximately 60–1000 times higher than that of conventional CVD.     

Electrochemical performance of nano-SiO2 modified LiCoO2 thin films fabricated by electrostatic spray deposition (ESD)

With a mixture of a SiO₂ sol and a solution of lithium and cobalt acetates as the precursor, nano-SiO₂ modified LiCoO₂ films were fabricated by the electrostatic spray deposition (ESD) technique. The SiO₂ content of these films was 0, 5, 10, 15 and 20 wt%, respectively. Their structure and electrochemical properties were characterized by means of X-ray diffraction, scanning electron microscopy, galvanostatic cell cycling, AC impedance spectroscopy and cyclic voltammetry. Li₂CoSiO₄ was found formed in the SiO₂-containing films. The film with 15 wt% SiO₂ shows the best cycling stability with the capacity of 130 mAh/g in the voltage range between 2.7 and 4.3 V at the current density of 0.1 mA/cm². Due to its resulted small cell impedance, it has excellent rate capability. A LiCoO₂ (shell)/SiO₂ (core) structure model is proposed to explain the improved properties of these films.     

A comparison of La0.75Sr0.25Cr0.5Mn0.5O3−δ and Ni impregnated porous YSZ anodes fabricated in two different ways for SOFCs

In this paper, La_0.75Sr_0.25Cr_0.5Mn_0.5O_3−δ (LSCrM) and Ni impregnated porous yttria-stabilized zirconia (YSZ) anodes have been fabricated in two different ways. The testing results demonstrated the excellent performance of the anode made by infiltrating a mixture of LSCrM and Ni(NO₃)₂ solutions into porous YSZ matrix. After reduction of the anode with hydrogen, an inner nano-network structure with mixed ionic-electronic conducting path has been formed within and between these added particles. A single cell with the anode at 800 °C exhibited the maximum power densities of 1151 and 704 mW cm⁻² when dry H₂ and CH₄ were used as the fuels, respectively; under the same conditions, the cell performances for LSCrM and Ni impregnated YSZ anode separately were 810 and 508 mW cm⁻². A cavity model was proposed to simulate the impregnating process and the loading was calculated. No carbon deposition was detected in the anode, even with the presence of Ni, after operation in dry CH₄ for about 6 h under open-circuit condition.     

Preparation and characterization of Bi-doped antimony selenide thin films by electrodeposition

Bi-doped antimony selenide (Sb_2−xBi_xSe₃) thin films have been prepared by potentiostatical electrodeposition and post annealing treatment. Cyclic voltammetry (CV) was used to investigate the electrochemical behaviors of electrodeposition. The suitable deposition potential for film preparation was determined to be about −0.40 V vs. SCE combining with CV, energy dispersive X-ray spectroscopy (EDS), environmental scanning electron microscope (ESEM) studies. After annealing, film shows improved crystallinity and a basic orthorhombic Sb₂Se₃ structure but having a larger d-spacing due to the substitution of Bi for Sb in Sb₂Se₃ lattice. The annealed film exhibits an absorption coefficient of larger than 10⁵ cm⁻¹ in the visible region, an direct optical band gap of 1.12 ± 0.01 eV, the n-type conductivity, an carrier concentration of 1.1 × 10¹⁹ cm⁻³ and an flat band potential of −0.40 ± 0.03 V vs. SCE.     

Enhanced electrochemical properties of Bi-layer La0.5Sr0.5CoO3−δ cathode prepared by a hybrid method

Bi-layer La_0.5Sr_0.5CoO_3−δ (LSCO) cathodes are processed by a hybrid method that combines a seed layer prepared by a pulsed laser deposition (PLD) technique and a conventional cathode layer (∼7 μm in thickness) by a screen printing method. By inserting the PLD seed layer with the thickness of ∼500 nm or less, robust cathode films with desired microstructure and excellent adhesion properties with the underlying electrolyte layer, are successfully fabricated. The area specific resistance (ASR) of the hybrid cathode layers decreases about 5 times compared with that of the single layer cathode films prepared by the conventional screen printing method. The hybrid approach provides a cost-effective way to fabricate thick cathode films with significantly enhanced electrochemical properties for solid oxide fuel cells (SOFCs).     

Preparation and characterization of CeO2/TiO2 nanoparticles by flame spray pyrolysis

Nanocrystalline TiO₂, CeO₂ and CeO₂-doped TiO₂ have been successfully prepared by one-step flame spray pyrolysis (FSP). Resulting powders were characterized with X-ray diffraction (XRD), N₂-physisorption, Transmission Electron Microscopy (TEM) and UV-Vis spectrophotometry. The TiO₂ and CeO₂-doped TiO₂ nanopowders were composed of single-crystalline spherical particles with as-prepared primary particle size of 10-13 nm for Ce doping concentrations of 5-50 at%, while square-shape particles with average size around 9 nm were only observed from flame-made CeO₂. The adsorption edge of resulting powder was shifted from 388 to 467 nm as the Ce content increased from 0 to 30 at% and there was an optimal Ce content in association with the maximum absorbance. This effect is due to the insertion of Ce^3+/4+ in the TiO₂ matrix, which generated an n-type impurity band.     

High performance electrode for electrochemical oxygen generator cell based on solid electrolyte ion transport membrane

A double-layer composite electrode based on Ba_0.5Sr_0.5Co_0.8Fe_0.2O_3−δ + Sm_0.2Ce_0.8O_1.9 (BSCF + SDC) and BSCF + SDC + Ag was investigated to be a promising cathode and also anode for the electrochemical oxygen generator based on samaria doped ceria electrolyte. The Ag particles in the second layer were not only the current collector but also the improver for the oxygen adsorption at the electrode. a.c. impedance results indicated that the electrode polarization resistance, as low as 0.0058 Ω cm² was reached at 800 °C under air. In oxygen generator cell performance test, the electrode resistance dropped to half of the value at zero current density under an applied current density of 2.34 A cm⁻² at 700 °C, and on the same conditions the oxygen generator cell was continual working for more than 900 min with a Faradic efficiency of ∼100%.     

Synthesis and microstructure of (LaSr)MnO3 and (LaSr)FeO3 ceramics by a reaction-sintering process

(La_xSr_1−x)MnO₃ (LSMO) and (La_xSr_1−x)FeO₃ (LSFO) (x = 0.2–0.4) ceramics prepared by a simple and effective reaction-sintering process were investigated. Without any calcination involved, La₂O₃ and SrCO₃ were mixed with MnO₂ (LSMO) or Fe₂O₃ (LSFO) then pressed and sintered directly. LSMO and LSFO ceramics were obtained after 2 and 4 h sintering at 1350–1400 and 1200–1280 °C, respectively. Grain size decreased as La content increased in LSMO and LSFO ceramics.     

Preparation, characterization and electrical conductivity studies of NdYb1−xGdxZr2O7 (0 ≤ x ≤ 1.0) ceramics

Several compositions of NdYb_1−xGd_xZr₂O₇ (0 ≤ x ≤ 1.0) ceramics were prepared by pressureless-sintering method at 1973 K for 10 h in air. The relative density, microstructure and electrical conductivity of NdYb_1−xGd_xZr₂O₇ ceramics were analyzed by the Archimedes method, X-ray diffraction, scanning electron microscopy and impedance plots measurements. NdYb_1−xGd_xZr₂O₇ (0 ≤ x ≤ 0.3) ceramics have a single phase of defect fluorite-type structure, and NdYb_1−xGd_xZr₂O₇ (0.7 ≤ x ≤ 1.0) ceramics exhibit a single phase of pyrochlore-type structure; however, the NdYb_0.5Gd_0.5Zr₂O₇ composition shows mixed phases of both defect fluorite-type and pyrochlore-type structures. The measured values of the grain conductivity obey the Arrhenius relation. The grain conductivity of each composition in NdYb_1−xGd_xZr₂O₇ ceramics gradually increases with increasing temperature from 673 to 1173 K. NdYb_1−xGd_xZr₂O₇ ceramics are oxide-ion conductor in the oxygen partial pressure range of 1.0 × 10⁻⁴ to 1.0 atm at all test temperature levels. The highest grain conductivity value obtained in this work is 1.79 × 10⁻² S cm⁻¹ at 1173 K for NdYb_0.3Gd_0.7Zr₂O₇ composition.     

Effects of cathode fabrication conditions and cycling on the electrochemical performance of LiNiO2 synthesized by combustion and calcination

LiNiO₂ was synthesized by the combustion method with various excess lithium amount z in Li_1 + zNiO₂ (z = 0.04, 0.08, 0.10, 0.12, and 0.15). The sample with z = 0.10 has the largest first discharge capacity of 195 mAh/g at 0.1 C rate and voltage range 2.7-4.4 V with the weight ratio of active material:acetylene black:binder = 85:10:5. The LiNiO₂ cathodes, in which the excess lithium amount z for the synthesis of LiNiO₂ was 0.10, were fabricated with various weight ratios of active material:acetylene black:binder (85:10:5, 85:12:3, and 90:7:3). The cathode with the ratio of active material:acetylene black:binder 85:10:5 has the best electrochemical properties. The variation, with C-rate, of discharge capacity vs. number of cycles curve for the LiNiO₂ cathode with the weight ratio of active material:acetylene black:binder = 85:10:5 was investigated. At 0.1 C rate, the LiNiO₂ cathode has the largest first discharge capacity, the discharge capacity degradation rate of 0.70 mAh/g/cycle and a discharge capacity at n = 50 of 134 mAh/g.     

Fabrication and characterization of composite electrolyte for intermediate-temperature SOFC

In this study, a ceria-based composite electrolyte was investigated for intermediate-temperature solid oxide fuel cells (SOFCs) based on SDC-25 wt.% K₂CO₃. Sodium carbonate co-precipitation process by which SDC powder was adopted and sound cubic fluorite structure was formed after SDC powders were sintered at 750 °C for 3 h. The crystallite size of the particle was 21 nm in diameter as calculated from data obtained through X-ray diffraction. The conductivity of the composite electrolyte proposed in this study was much higher than that of pure SDC at the comparable temperature of 550-700 °C. The transition of the ionic conductivity occurred at 650 °C. Based on this type of composite electrolyte, single cell with the electrolyte thickness of 0.3 mm were fabricated using dry pressing, with nickel oxide adopted as anode and SSC as cathode. The single cell was then tested at 550-700 °C on home-made equipment in this study, using hydrogen/air. The maximum power density and open circuit voltage (OCV) achieved 600 mW cm⁻² and 1.05 V at 700 °C, respectively.     

Preparation and characterization of multicomponent porous materials prepared by the sol-gel process

An experimental strategy was developed to obtain transparent Si-Al-Ti-Ni-Mo and Si-Zr-Ti-Ni-Mo sols via the sol-gel process. The sol was prepared from Si(OEt)₄ (TEOS), Al(OBu^s)₃ (OBu^s: C₂H₅CH(CH₃)O), Ti(OEt)₄ (OEt: OCH₂CH₃), Zr(OPrⁿ)₄ (OPrⁿ: OCH₂CH₂CH₃). In both cases nickel nitrate hexahydrate (Ni(NO₃)₂ · 6H₂O) and ammonium heptamolybdate tetrahydrate ((NH₄)₆Mo₇O₂₄ · 4H₂O) were the Ni and Mo sources, respectively. The sols were characterized by Fourier Transform Infrared Spectroscopy (FTIR). Assignments of the simultaneous formation of the Si-O-Al, Si-O-Ti, Si-O-Ni, and Si-O-Zr bonds were done. The sols were polymerized at room temperature (293 K) to obtain gels, and these were dried at 423 K and calcined at 573, 853 and 893 K in air. The characterization techniques used were small-angle X-ray scattering (SAXS), X-ray diffraction (XRD), scanning electron microscopy (SEM), and ²⁹Si and ²⁷Al magic angle spinning nuclear magnetic resonance (MAS NMR). The density of the solids was measured following ASTM method D-4892 and the porosity and surface area were determined by N₂ adsorption/desorption isotherms. The corresponding average pore diameters were evaluated using the BJH, HK, and DA methods.     

A bi-layered composite cathode of La0.8Sr0.2MnO3-YSZ and La0.8Sr0.2MnO3-La0.4Ce0.6O1.8 for IT-SOFCs

A bi-layered composite cathode of La_0.8Sr_0.2MnO₃ (LSM)-YSZ and LSM-La_0.4Ce_0.6O_1.8 (LDC) was fabricated for anode-supported solid oxide fuel cells with a thin YSZ electrolyte film. The cell with the bi-layered composite cathode displayed better performance than the cell with the corresponding single-layered composite cathode of LSM-LDC or LSM-YSZ. At 650 °C, the cell with the bi-layered composite cathode gave a higher maximum power density than the cells with the single-layered LSM-LDC and LSM-YSZ composite cathodes, by 52% and 175%, respectively. The impedance spectra results show that the thin LSM-YSZ interlayer not only improves the cathode/electrolyte interface but also reduces the polarization resistance of the cathode. The activation energy for oxygen reduction on the bi-layered composite cathode is much smaller than that on LSM-YSZ composite cathode, and it is suggested that the special redox property of Ce⁴⁺/Ce³⁺ in LDC facilitates the oxygen reduction process on the bi-layered composite cathode. The cell with the bi-layered composite cathode operated quite stably during a 100 h run.     

Preparation, characterization and electrocatalytic properties of poly(luminol) and polyoxometalate hybrid film modified electrodes

Hybrid films composed of poly(luminol) and nanometer-sized clusters of polyoxometalate, SiMo₁₂O₄₀⁴⁻ and PMo₁₂O₄₀³⁻ have been prepared in acidic aqueous solutions. These films are stable and electrochemically active, and produced on glassy carbon, platinum, gold and transparent semiconductor tin oxide electrodes. The electrochemical quartz crystal microbalance and cyclic voltammetry were used to study in situ growth of the hybrid poly(luminol)/SiMo₁₂O₄₀⁴⁻ and poly(luminol)/PMo₁₂O₄₀³⁻. Both the poly(luminol)/SiMo₁₂O₄₀⁴⁻ and poly(luminol)/PMo₁₂O₄₀³⁻ hybrid films showed four redox couples and the electrochemical properties were compared to SiMo₁₂O₄₀⁴⁻ and PMo₁₂O₄₀³⁻. When transferred to various acidity aqueous solutions, the four redox couples and the formal potentials of two hybride film were observed to be pH-dependent. The electrocatalytic reduction of ClO₃⁻, BrO₃⁻, IO₃⁻, S₂O₈²⁻ and NO₂⁻ by a poly(luminol)/PMo₁₂O₄₀³⁻ hybrid film in an acidic aqueous solution showed an electrocatalytic reduction activity of IO₃⁻ > BrO₃⁻ and ClO₃⁻. The electrocatalytic oxidation of dopamine and epinephrine by a poly(luminol)/PMo₁₂O₄₀³⁻ hybrid film was also investigated.     

Electrical and stability performance of anode-supported solid oxide fuel cells with strontium- and magnesium-doped lanthanum gallate thin electrolyte

Anode-supported solid oxide fuel cells (SOFCs) comprising NiO-samarium-doped ceria (SDC) (Sm_0.2Ce_0.8O_1.9) composite anode, thin tri-layer electrolyte, and La_0.6Sr_0.4Co_0.8Fe_0.2O₃ (LSCF)-La_0.9Sr_0.1Ga_0.8Mg_0.2O_3−δ (LSGM) composite cathode were fabricated. The thin tri-layer consisting of an 11-μm thick LSGM electrolyte layer and a 12-μm thick La_0.4Ce_0.6O_1.8 (LDC) layer on each side of the LSGM was prepared by centrifugal casting and co-firing technique. The performance of the cells operated with humidified H₂ as fuel and ambient air as oxidant showed a maximum power density of 1.23 W cm⁻² at 800 °C. A stability test of about 100 h was carried out and some deterioration of output power was observed, while the open circuit voltage (OCV) kept unchanged. Impedance measurements showed that both the electrolyte ohmic resistance and the electrode polarization increased with time and the latter dominated the degradation.     

Ferroelectric and structural instability of (Pb,Ca)TiO3 thin films prepared in an oxygen atmosphere and deposited on LSCO thin films which act as a buffer layer

Structural, microstructural and ferroelectric properties of Pb_0.90Ca_0.10TiO₃ (PCT10) thin films deposited using La_0.50Sr_0.50CoO₃ (LSCO) thin films which serve only as a buffer layer were compared with properties of the thin films grown using a platinum-coated silicon substrate. LSCO and PCT10 thin films were grown using the chemical solution deposition method and heat-treated in an oxygen atmosphere at 700 °C and 650 °C in a tube oven, respectively. X-ray diffraction (XRD) and Raman spectroscopy results showed that PCT10 thin films deposited directly on a platinum-coated silicon substrate exhibit a strong tetragonal character while thin films with the LSCO buffer layer displayed a smaller tetragonal character. Surface morphology observations by atomic force microscopy (AFM) revealed that PCT10 thin films with a LSCO buffer layer had a smoother surface and smaller grain size compared with thin films grown on a platinum-coated silicon substrate. Additionally, the capacitance versus voltage curves and hysteresis loop measurement indicated that the degree of polarization decreased for PCT10 thin films on a LSCO buffer layer compared with PCT10 thin films deposited directly on a platinum-coated silicon substrate. This phenomenon can be described as the smaller shift off-center of Ti atoms along the c-direction 〈001〉 inside the TiO₆ octahedron unit due to the reduction of lattice parameters. Remnant polarization (P_r) values are about 30 μC/cm² and 12 μC/cm² for PCT10/Pt and PCT10/LSCO thin films, respectively. Results showed that the LSCO buffer layer strongly influenced the structural, microstructural and ferroelectric properties of PCT10 thin films.     

One-step electrochemical preparation of the ternary (BixSb1−x)2Te3 thin films on Au(1 1 1): Composition-dependent growth and characterization studies

This study reports on the synthesis of ternary semiconductor (Bi_xSb_1−x)₂Te₃ thin films on Au(1 1 1) using a practical electrochemical method, based on the simultaneous underpotential deposition (UPD) of Bi, Sb and Te from the same solution containing Bi³⁺, SbO⁺, and HTeO₂⁺ at a constant potential. The thin films are characterized by X-ray diffraction (XRD), atomic force microscopy (AFM), energy dispersive spectroscopy (EDS) and reflection absorption-FTIR (RA-FTIR) to determine structural, morphological, compositional and optic properties. The ternary thin films of (Bi_xSb_1−x)₂Te₃ with various compositions (0.0 ≤ x ≤ 1.0) are highly crystalline and have a kinetically preferred orientation at (0 1 5) for hexagonal crystal structure. AFM images show uniform morphology with hexagonal-shaped crystals deposited over the entire gold substrate. The structure and composition analyses reveal that the thin films are pure phase with corresponding atomic ratios. The optical studies show that the band gap of (Bi_xSb_1−x)₂Te₃ thin films could be tuned from 0.17 eV to 0.29 eV as a function of composition.     

IrO2-SiO2 binary oxide films: Preparation, physiochemical characterization and their electrochemical properties

Mixed IrO₂-SiO₂ oxide films were prepared on titanium substrate by the thermo-decomposition of hexachloroiridate (H₂IrCl₆) and tetraethoxysilane (TEOS) mixed precursors in organic solvents. The solution chemistry and thermal decomposition kinetics of the mixed precursors were investigated by ultra violet/visible (UV/vis) spectroscopy and thermogravimetry (TGA) and differential thermal analysis (DTA), respectively. The physiochemical characterization of the resulting materials was conducted by X-ray diffraction (XRD), scanning electron microscopy (SEM) and electrochemical measurements. It is shown from the UV/vis spectra that the electronic absorption intensity of IrCl₆²⁻ complexes in the precursors decreases in the presence of TEOS, indicating the interaction between these two components. Thermal analysis shows the decomposition reaction of H₂IrCl₆ is inhibited by TEOS in the low temperature range, but the further oxidation reaction at high temperatures of formed intermediates is independent of the presence of silane component. Physical measurements show a restriction effect of silica on the crystallization and crystal growth processes of IrO₂, leading to the formation of finer oxide particles and the porous morphology of the binary oxide films. The porous composite films exhibit high apparent electrocatalytic activity toward the oxygen evolution reaction. In addition, the long-term stability of Ti-supported IrO₂ electrodes is found to apparently improve with appropriate amount of SiO₂ incorporation, as tested under galvanostatic electrolysis.     

Capacitive and textural characteristics of hydrous manganese oxide prepared by anodic deposition

The amorphous hydrous manganese oxide (denoted as a-MnO_x·nH₂O) was anodically deposited from the MnSO₄ solutions of various pH values. The capacitive characteristics and stability of this oxide without and with annealing in air for 2 h up to 400 °C were systematically investigated in aqueous electrolytes through means of cyclic voltammetry (CV) and the constant-current charge-discharge method. The redox properties of a-MnO_x·nH₂O were strongly affected by the electrolytes employed and this oxide exhibited ideally capacitive behavior in 0.1 M Na₂SO₄ and 0.3 M KCl. The stability of this amorphous hydrous oxide was enhanced by the annealing treatment while its capacitance was gradually decreased with increasing the annealing temperature. The amorphous structure and surface morphologies of a-MnO_x·nH₂O with annealing at different temperatures were, respectively, examined in terms of the X-ray diffraction (XRD) patterns and scanning electron microscopic (SEM) photographs. The oxidation states of these a-MnO_x·nH₂O deposits were studied by X-ray photoelectron spectroscopy (XPS).