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.     

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.     

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.     

High performance of proton-conducting solid oxide fuel cell with a layered PrBaCo2O5+δ cathode

A dense BaZr_0.1Ce_0.7Y_0.2O_3−δ (BZCY) electrolyte is fabricated on a porous anode by in situ drop-coating method which can lead to extremely thin electrolyte membrane (10 μm in thickness). The layered perovskite structure oxide PrBaCo₂O_5+δ (PBCO) is synthesized by auto ignition process and initially examined as a cathode for proton-conducting IT-SOFCs. The electrical conductivity of PrBaCo₂O_5+δ (PBCO) reaches the general required value for the electrical conductivity of cathode absolutely. The single cell, consisting of PrBaCo₂O_5+δ (PBCO)/BaZr_0.1Ce_0.7Y_0.2O_3−δ (BZCY)/NiO-BaZr_0.1Ce_0.7Y_0.2O_3−δ (BZCY) structure, is assembled and tested from 600 to 700 °C with humidified hydrogen (3% H₂O) as the fuel and air as the oxidant. An open-circuit potential of 1.01 V and a maximum power density of 545 mW cm⁻² at 700 °C are obtained for the single cell, and a low polarization resistance of the electrodes of 0.15 Ω cm² is achieved at 700 °C.     

Surface exchange and bulk diffusion properties of Ba0.5Sr0.5Co0.8Fe0.2O3−δ mixed conductor

Ba_0.5Sr_0.5Co_0.8Fe_0.2O_3−δ (BSCF) is a mixed conducting oxide that shows high oxygen permeability to perform as a ceramic membrane and high electrochemical activity for oxygen reduction to perform as a cathode of solid oxide fuel cells. Both performances are closely related to the bulk and surface properties of the BSCF oxide. In this study, the chemical bulk diffusion coefficient (D_chem) and chemical surface exchange coefficient (k_chem) of BSCF at various temperatures and oxygen partial pressures are determined by an electrical conductivity relaxation (ECR) method. Both D_chem and k_chem are found to be dependent on pO₂ with positive effect. Ea of D_chem and k_chem are respectively 111 ± 5 and 110 ± 6 kJ mol⁻¹ between 600 and 800 °C. Oxygen-ion diffusion and tracer diffusion coefficients are estimated from D_chem and compared with the literature results. Ionic conductivities are further derived according to the Nernst-Einstein relation. The poisoning effect of CO₂ on the performances of BSCF is further investigated by the ECR method in combination with oxygen temperature-programmed desorption technique. The presence of CO₂ causes a substantial decrease in k_chem, however, the surface kinetics can be recovered by performing re-calcination in an oxidative atmosphere at 900 °C, agreeing well with literature reports.     

Characterization of electrolytic Co3O4 thin films as anodes for lithium-ion batteries

The electrolytic deposition of Co₃O₄ thin films on stainless steel was conducted in Co(NO₃)₂ aqueous solution for anodes in lithium-ion thin film batteries. Three major electrochemical reactions during the deposition were discussed. The coated specimens and the coating films carried out at −1.0 V (saturated KCl Ag/AgCl) were subjected to annealing treatments and further characterized by XRD, TGA/DTA, FE-SEM, Raman spectroscopy, cyclic voltammetry (CV) and discharge/charge cyclic tests. The as-coated film was β-Co(OH)₂, condensed into CoO and subsequently oxidized into nano-sized Co₃O₄ particles. The nano-sized Co₃O₄, CoO, Li₂O and Co particles revealed their own characteristics different from micro-sized ones, such as more interfacial effects on chemical bonding and crystallinity. The initial maximum capacity of Co₃O₄ coated specimen was 1930 mAh g⁻¹ which much more than its theoretical value 890 mAh g⁻¹, since the nano-sized particles offered more interfacial bondings for extra sites of Li⁺ insertion. However, a large ratio of them was trapped, resulting in a great part of irreversible capacity during the first charging. Still, it revealed a capacity 500 mAh g⁻¹ after 50 discharged-charged cycles.     

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 and characterization of semiconducting Zn1−xCdxSe thin films

The electrodeposition of Zn_1−xCd_xSe polycrystalline semiconducting thin films from aqueous acidic bath without any additives onto tin oxide-coated conducting glass and titanium substrates are described. The influence of deposition parameters on the film formation and deposition mechanism based on cyclic voltammetry is discussed. X-ray diffraction studies showed the polycrystalline wurtzite nature for all the films deposited under the proposed conditions. The optical studies revealed the band gap values in the range between 2.82 and 1.72 eV as the film composition changes from ZnSe to CdSe. It has been observed that the concentration of cadmium salt plays an essential role on the alloy formation. The surface morphological studies and composition analysis were carried out and the results are discussed.     

Chemical diffusivity and ionic conductivity of GdBaCo2O5+δ

The transport properties of layered perovskite GdBaCo₂O_5+δ (GBCO), which has recently been proposed as a cathode material for intermediate-temperature solid oxide fuel cells (IT-SOFCs), are investigated as a function of oxygen partial pressure (OPP) over the oxygen partial pressure range of 10⁻⁴ ≤ pO₂ (atm) ≤ 0.21 at 1073 ≤ T (K) ≤ 1323. The increase in total conductivity with increasing temperature below the low-temperature, order–disorder transition indicates a semiconductor-type behaviour with an activation energy of 0.42 eV. When OPP is increased to air pressure at a fixed temperature, the total conductivity increases with an apparent slope (∂log σ/∂log pO₂) of 1/10 to 1/22. The maximum oxygen ion conductivity, as extracted from the oxygen permeation measurements, is around 0.01 S cm⁻¹ under the nitrogen condition, which strongly supports the potential for cathode application. The chemical diffusion coefficient () and surface exchange coefficient (κ) are also calculated from the d.c. conductivity relaxation measurement and the values are best fitted by the following two equations:     

Novel cobalt-free cathode materials BaCexFe1−xO3−δ for proton-conducting solid oxide fuel cells

A series of cobalt-free and low cost BaCe_xFe_1−xO_3−δ (x = 0.15, 0.50, 0.85) materials are successful synthesized and used as the cathode materials for proton-conducting solid oxide fuel cells (SOFCs). The single cell, consisting of a BaZr_0.1Ce_0.7Y_0.2O_3−δ (BZCY7)-NiO anode substrate, a BZCY7 anode functional layer, a BZCY7 electrolyte membrane and a BaCe_xFe_1−xO_3−δ cathode layer, is assembled and tested from 600 to 700 °C with humidified hydrogen (3% H₂O) as the fuel and the static air as the oxidant. Within all the cathode materials above, the cathode BaCe_0.5Fe_0.5O_3−δ shows the highest cell performance which could obtain an open-circuit potential of 0.99 V and a maximum power density of 395 mW cm⁻² at 700 °C. The results indicate that the Fe-doped barium cerates can be promising cathodes for proton-conducting SOFCs.     

Preparation of CuIn1−xGaxSe2 thin films by sputtering and selenization process

CuIn_1−xGa_xSe₂ polycrystalline thin films were prepared by a two-step method. The metal precursors were deposited either sequentially or simultaneously using Cu–Ga (23 at%) alloy and In targets by DC magnetron sputtering. The Cu–In–Ga alloy precursor was deposited on glass or on Mo/glass substrates at either room temperature or 150°C. These metallic precursors were then selenized with Se pellets in a vacuum furnace. The CuIn_1−xGa_xSe₂ films had a smooth surface morphology and a single chalcopyrite phase.     

Floating zone growth of β-Ga2O3: a new window material for optoelectronic device applications

β-Ga₂O₃ is a transparent oxide and intrinsically an insulator. Doping allows the variation of the conductivity for both p- and n-type over a wide range. There are a number of potential applications in optoelectronics such as insulating or conductive window material, or as a substrate. Consequently, the influence of doping on the electrical and optical properties is an issue of crucial importance for pushing this material forward to applications. We report on the successful growth of undoped, Ge- and Ti-doped β-Ga₂O₃ single crystals by the floating zone technique. Both electrical and optical properties were characterized.     

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%.     

Phase transitions and phase decomposition of La1−xSrxCoO3−δ in low oxygen partial pressures

High-temperature X-ray diffraction has been used to investigate the phase stability of lanthanum strontium cobalt oxide (LSC) for a range of materials with the formula La_1−xSr_xCoO_3−δ (x = 0.7, 0.4, and 0.2). The stability of LSC increases with La content in low oxygen partial pressures at high temperature. Oxygen vacancy ordering has been observed for all three compositions in either low oxygen pressure or under reducing gas, as evidenced by the formation of the brownmillerite phase. The crystal structure of the vacancy-ordered phase was determined using Rietveld analysis of synchrotron X-ray diffraction data. The decomposition products under low oxygen pressure and in reducing conditions have been identified and characterized, including the phase transition and thermal expansion of the primary decomposition products, LaSrCoO₄ and LaSrCoO_3.5.     

Structural and optical characterization of hot wall deposited CdSexTe1−x films

CdSe_0.3Te_0.7 alloy was prepared from the individual components and its composition and structural analysis were done. Films were prepared by hot wall deposition technique using 0.15 m length tube under a vacuum of 5×10⁻⁵ Torr on well cleaned glass substrates. The composition, structural, morphological, and optical properties of hot wall deposited films were investigated. The XRD analysis revealed that the films are like amorphous in nature for lower thicknesses but with increasing thickness a more preferred orientation along (1 0 1) direction was observed. The crystallite size (D), dislocation density (δ) and strain () were evaluated. From the EDX composition analysis, the individual concentrations of Se and Te in the films were estimated. An analysis of optical measurements shows that all the films have fairly good transparency above 850 nm. The optical band gap was found to be around 1.55 eV and decreases with increasing thickness. Also comparison of band gap with corresponding values for CdSe and CdTe are made.     

Layered GdBa0.5Sr0.5Co2O5+δ as a cathode for intermediate-temperature solid oxide fuel cells

The layered GdBa_0.5Sr_0.5Co₂O_5+δ (GBSC) perovskite oxides are synthesized by Pechini method and investigated as a novel cathode material for intermediate-temperature solid oxide fuel cells (IT-SOFCs). The single cell of NiO–SDC (Sm_0.2Ce_0.8O_1.9)/SDC (20 μm)/GBSC (10 μm) is operated from 550 to 700 °C fed with humidified H₂ as fuel and the static air as oxidant. An open circuit voltage of 0.8 V and a maximum power density of 725 mW cm⁻² are achieved at 700 °C. The interfacial polarization resistance is as low as 0.88, 0.29, 0.13 and 0.05 Ω cm² at 550, 600, 650 and 700 °C, respectively. The ratio of polarization resistance to total cell resistance decreases with the increase in the operating temperature, from 60% at 550 °C to 21% at 700 °C, respectively. The experimental results indicate that GBSC is a promising cathode material for IT-SOFCs.     

High performance layered SmBa0.5Sr0.5Co2O5+δ cathode for intermediate-temperature solid oxide fuel cells

The layered SmBa_0.5Sr_0.5Co₂O_5+δ (SBSC) perovskite oxide is synthesized by the Pechini method and investigated as a novel cathode material for intermediate-temperature solid oxide fuel cells (IT-SOFCs). A laboratory-sized Sm_0.2Ce_0.8O_1.9 (SDC)-based tri-layer cell of NiO–SDC/SDC/SBSC is operated from 500 to 700 °C fed with humidified H₂ (3% H₂O) as a fuel and the static ambient air as oxidant. A maximum power density of 1147 mW cm⁻² is achieved at 700 °C. The interfacial polarization resistance is as low as 1.01, 0.38, 0.16, 0.06 and 0.03 Ω cm² at 500, 550, 600, 650 and 700 °C, respectively. The experimental results indicate that SBSC is a very promising cathode material for IT-SOFCs.     

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.     

Solar cells with Cu(In1−xGax)S2 thin films prepared by sulfurization

By rapid thermal processing of Cu/In/GaS precursors, good-quality CuIn_1–xGa_xS₂ films are synthesized. By suppressing the formation of In-rich hillocks, we could obtain homogeneous CuIn_1–xGa_xS₂ surfaces. A conversion efficiency of 12% has been achieved using a relatively low (1.2) Cu/In ratio.     

A screen-printed Ce0.8Sm0.2O1.9 film solid oxide fuel cell with a Ba0.5Sr0.5Co0.8Fe0.2O3−δ cathode

Screen-printing technology was developed to fabricate Ce_0.8Sm_0.2O_1.9 (SDC) electrolyte films onto porous NiO–SDC green anode substrates. After sintering at 1400 °C for 4 h, a gas-tight SDC film with a thickness of 12 μm was obtained. A novel cathode material of Ba_0.5Sr_0.5Co_0.8Fe_0.2O_3−δ was subsequently applied onto the sintered SDC electrolyte film also by screen-printing and sintered at 970 °C for 3 h to get a single cell. A fuel cell of Ni–SDC/SDC (12 μm)/Ba_0.5Sr_0.5Co_0.8Fe_0.2O_3−δ provides the maximum power densities of 1280, 1080, 670, 370, 180 and 73 mW cm⁻² at 650, 600, 555, 505, 455 and 405 °C, respectively, using hydrogen as fuel and stationary air as oxidant. When dry methane was used as fuel, the maximum power densities are 876, 568, 346 and 114 mW cm⁻² at 650, 600, 555 and 505 °C, respectively. The present fuel cell shows excellent performance at lowered temperatures.