The effect of annealing on the electrochemical properties of Zr0.5Ti0.5Mn0.5V0.3Co0.2Ni1.1 alloy electrodes

The annealing treatment was found to result in the improvement in the cyclic stability but the degradation of discharge capacity, activation and high-rate dischargeability for Zr_0.5Ti_0.5Mn_0.5V_0.3Co_0.2Ni_1.1 alloy electrode. A lower discharge potential in the annealed alloy electrode was found owing to a more homogeneous alloy, which is consistent with the pressure–composition isotherms (P–C–T) measurement. We found that the annealed alloy also had lower and flatter pressure plateaus, and larger pressure hysteresis. At high discharge rates, the hydrogen diffusion in the bulk of the alloy was the rate-determining step. The diffusion coefficients for hydrogen in the annealed and as-cast alloys were calculated to be 1.4×10⁻¹² cm² s⁻¹ and 4.3×10⁻¹² cm² s⁻¹, respectively. The lowering of high-rate discharge capacity can be ascribed to the reason that the hydrogen diffusion coefficient is lower due to homogeneous microstructure in the annealed alloy.     

Preparation and properties of transparent conducting zinc oxide and aluminium-doped zinc oxide films prepared by evaporating method

Undoped and aluminium-doped zinc oxide films have been prepared by thermal evaporation of zinc acetate [Zn(CH₃COO)₂ 2H₂O] and aluminium chloride [AlCl₃] onto a heated glass substrate. The structural and optoelectrical properties of the films have been studied. The effects of heat treatment for the as-deposited films in air and vaccum are investigated. Highly transparent films with conductivity as low as 2×10⁻³ Ω cm can be produced by controlling the deposition parameters. The electron carrier densities are in the range 0.2–7×10¹⁹ cm⁻³ with mobilities of 22–58 cm² V⁻¹ s⁻¹.     

Kinetics of the NCO radical reacting with atoms and selected molecules

Rate constants for the reaction of isocyanate radicals (NCO) in its electronic ground state ( ²Π) with oxygen atoms were determined at 2.5 Torr total pressure in the temperature range 302–757 K. Excimer laser photolysis (ELP) of chlorine isocyanate (ClNCO) produced NCO radicals detected by laser-induced fluorescence (LIF). The reaction NCO + O exhibits a negative temperature dependence, described by the two-parameter equation: k_NCO+O(T) = (4.3_−2.2^+3.2) × 10⁻⁸ × T^{−1.14_−0.12+0.08} cm³ molecule⁻¹ s⁻¹. Measurements at 298 K and total pressures of 2.5 and 9.9 Torr, respectively, indicated a slight pressure dependence. For the reaction of NCO radicals with hydrogen atoms, the rate constant k_NCO+H = (2.2 ± 1.5) × 10⁻¹¹ cm³ molecule⁻¹ s⁻¹was obtained at 298 K and a total pressure of 2.6 Torr for the first time by a direct measurement. From a single measurement k = (3.8 ± 1.6) × 10⁻¹¹ cm³ molecule⁻¹ s⁻¹ was determined at 548 K and 2.4 Torr total pressure. In addition, rate constants for the reactions of NCO radicals with molecular oxygen (O₂), carbon dioxide (CO₂), molecular hydrogen (H₂), and carbon monoxide (CO), which is a dissociation product of CO₂ in a microwave discharge, were measured at two different temperatures. At room temperature these reactions were slow and at the detection limit of the ELP/LIF technique. However, at elevated temperatures at least the rate constants of the reactions NCO + O₂ and NCO + H₂ become significantly larger and, therefore, should be taken into account, when modeling combustion processes under certain conditions.     

Electrical and optical properties of F-doped textured SnO2 films deposited by APCVD

This paper presents the structural, electrical and optical properties of transparent conducting F-doped textured SnO₂ films prepared by atmosphere pressure chemical vapour deposition (APCVD). Polycrystalline SnO₂:F films having a variable preferred orientation have been obtained with resistivity as low as 5 × 10⁻⁴ Ωcm, with carrier concentrations between 3.5 × 10²⁰ and 7 × 10²⁰ cm⁻³, and Hall mobilities from 15.7 to 20.1 cm²/V/s. The average transmittance (including diffusion transmittance) is as high as 94% in the wavelength range of the visible spectrum and the maximum infrared reflectance reaches 92% for a film 655 nm thick. The figure of merit ƒ_TC = T10/_sh, (7.12 × 10⁻² S) of these films is the highest amongst the results reported on doped SnO₂ films.     

Oxygen reduction on platinum electrode coated with Nafion

The kinetics of the reduction of oxygen on platinum covered by a Nafion^® film in sulfuric acid (0.5 M) has been studied in order to determine to what extent the solid polymer electrolyte modifies this reaction. As electrode we used a rotating electrode which is particularly well adapted to the measurement of the permeability D_fC_f (product of the diffusion coefficient and of the oxygen concentration in the film) of oxygen in the Nafion^® film. This product is of the order of 6×10⁻¹² M cm⁻¹ s⁻¹ whatever the state of division of the platinum, and is of the same order of magnitude as the permeability D_sC_s of oxygen in the adjacent sulfuric acid solution. It is shown, moreover, that the oxygen concentration in the film is very high, about five times that in the solution.     

Electrochemistry of poly(vinylferrocene) modified electrodes in aqueous acidic media

A cyclic voltammetric study of the electrochemistry and chemical stability of the poly(vinylferrocene) (PVFc) redox couple, coated on a gold substrate, in aqueous solutions of H₂SO₄, HClO₄ and HCl was carried out. It was found that the anodic peak potential (E_pa) did not depend on the acid concentration in the range (1.0 × 10⁻² to 1.0 × 10⁻⁷ mol L⁻¹). However, the E_pa values shifted linearly to less positive potentials when investigated in more concentrated acid solutions in the range 1–5 mol L⁻¹. The slope of the E_pa versus acid concentration graph was found to be in the order H₂SO₄ > HCl > HClO₄. In this regard PVFc behaved very similar to 1,1′-bis(11-mercaptoundecyl)ferrocene (Fc(C₁₁SH)₂) except for its chemical stability. In H₂SO₄ media the PVFc was found to be much less stable than 1,1′-Fc(C₁₁SH)₂. The dependence of E_pa on acid concentration could be used to monitor state of charge of lead-acid batteries. However, for this application Fc(C₁₁SH)₂ would be a better choice because of its superior chemical stability.     

Polymer electrolyte membrane based on 2-acrylamido-2-methyl propanesulfonic acid fabricated by embedded polymerization

Methanol crossover through the Nafion membrane is a perennial problem in the operation of direct methanol fuel cells (DMFCs) and therefore justifies the search for a Nafion substitute. This study reports a new methanol-blocking polymer matrix which consists of a methanol barrier phase and an embedded proton source. A three-component polymer blend (TCPB) of poly(4-vinylphenol-co-methyl methacrylate), poly(butyl methacrylate) (PBMA), and Paraloid^® B-82 acrylic copolymer resins is used as a methanol barrier. In order to implant a proton source in the membrane as homogeneously as possible, the hydrophilic monomers, 2-acrylamido-2-methyl propanesulfonic acid (AMPS), 2-hydroxyethyl methacrylate (HEMA) and a cross-linking agent (poly(ethylene glycol) dimethylacrylate) (PEGDMA) are polymerized after they have been embedded in the TCPB matrix. The embedded polymerization has resulted in an asymmetric membrane structure, in which the hydrophilic network is sandwiched by two outer layers of predominantly hydrophobic TCPB. Measurements are made of properties of the AMPS-containing membranes that are important to fuel cell applications such as water uptake, ion-exchange capacity, proton conductivity, methanol permeability and tensile strength. The highest proton conductivity of the AMPS-containing membrane is about 0.030 S cm⁻¹ at 70 °C. The low methanol permeability (10⁻⁸ to 10⁻⁷ cm² s⁻¹) of the AMPS-containing membranes is their primary advantage for DMFC applications.     

Effect of rare earth oxides for improvement of MCFC

The solubility of rare earth metal oxides and their effect on the NiO solubility have been discussed to stabilize the cathode of molten carbonate fuel cells. The solubility of Ho, Yb, and Nd oxides were 4.4 × 10⁻⁴, 3.4 × 10⁻⁴, and 1.3 × 10⁻³ (mole fraction) at 923 K, respectively. The solubilities of NiO in (Li_0.52/Na_0.48)₂CO₃ with the saturated Ho, Yb, and Nd were 1.57 × 10⁻⁵, 1.41 × 10⁻⁵, and 9.5 × 10⁻⁶, respectively. Among these three, Nd, which has the highest solubility in the carbonates, reduced the NiO solubility most; although, the La reduced the NiO solubility more than Nd.

The logarithm of the solubility of the rare earth metal oxides has a linear relation to the Coulomb force ratio between the rare earth metal and the alkaline metal. Following this relation, the La should have the highest solubility among all the lanthanides. The basicity which NiO solubility closely relates has a linear relationship to the Coulomb force parameter of the melts. Based on these two models, the La would be the best additive to reduce the NiO solubility in Li/Na eutectic carbonate melt, among all the lanthanides.     

Synthesis and characterization of CuInSe2 thin films from Cu, In and Se stacked layers using a closed graphite box

Various techniques have been used to produce CuInSe₂ but the problem of producing films with the desired properties for efficient device fabrication over large areas has always persisted. The Stacked Elemental Layer (SEL) technique has been demonstrated as a method for producing films over a large area, but the films normally annealed in vacuum or in Se ambient, mostly exhibited poor morphology with small grain sizes which result in poor devices. A method of synthesizing CuInSe₂ films by annealing or selenization of the Cu, In and Se elemental layers using a closed graphite box was developed. SEM, EDX, XRD, spectrophotometric and Hall measurements were used to characterize all annealed films. Results have shown single phase chalcopyrite films with improved crystal sizes of about 4 μm The film composition varied from Cu-rich to In-rich with electrical resistivities of 10⁻³ to 10⁴ Ωcm, cattier concentrations of 5 × 10¹⁵ to 10¹⁷ cm⁻³ and mobilities of 0.6 to 7.8 cm² V⁻¹ s⁻¹ An energy band gap of 0.99 eV and 1.02 eV was obtained for a Cu-rich and near stoichiometric In-rich films respectively. Heterojunction devices using the structure ZnO/CdS/CuInSe₂ were fabricated with electrical conversion efficiencies of 6.5%.     

Methane-fueled IT-SOFCs with facile in situ inorganic templating synthesized mesoporous Sm0.2Ce0.8O1.9 as catalytic layer

Mesoporous Ce_0.8Sm_0.2O_1.9 (SDC) oxide with high surface area was prepared by a novel glycine-nitrate combustion process with in situ created nickel oxide as template, and applied as the catalytic layer for methane-fueled solid-oxide fuel cells (SOFCs) operated at reduced temperatures. The weight ratio of nickel oxide to SDC in the synthesis process was found to have significant effect on both the crystallite size and the textural properties of the resulted SDC powder. In particular, when it was at 9, the thermally stable and well-crystallized SDC powder showed a mesoporous structure with narrow pore-size distribution, high surface area (77 m² g⁻¹) and large pore volume (0.2276 cm³ g⁻¹), even after the calcination at 700 °C for 3 h. The mesoporous SDC was found to favor free gas diffusion with no gas diffusion polarization occurred even at high current density both for hydrogen and methane fuels. The SOFC with Ru impregnated mesoporous SDC catalytic layer displayed promising performance with a peak power density of 462 mW cm⁻² at 650 °C.     

Large area CIGS2 thin film solar cells on foils: nucleus of a pilot plant

In earlier research, conversion efficiency of 10.4% (AM1.5) and 9.9% (AM0) has been achieved on small area CuIn_xGa_1−xS₂ (CIGS2) solar cell on 127 μm thick stainless steel substrate. The area of research is mainly focused on studying CIGS2 thin films as solar cell absorber material and growing high efficiency cells on ultralightweight and flexible metallic foils such as 127 μm thick stainless steel and SiO₂ coated 25 μm thick Ti foils. This paper presents the scaling up process of CIGS2 thin film substrate from 2.5 × 2.5 cm² to 10 × 10 cm². Initial scaling up efforts focused on achieving uniform thickness and stress-free films. Process of scaling up consisted of refurbishment of selenization/sulfurization furnace, design and fabrication of scrubber and enlargement of new CdS deposition setup. The scaling up from 2.5 × 2.5 cm² to 10 × 10 cm² substrate size has laid the foundation for PV Materials Lab of Florida Solar Energy Center becoming the nucleus of a pilot plant.     

Long-term thermal cycling of Phlogopite mica-based compressive seals for solid oxide fuel cells

Planar solid oxide fuel cells (SOFCs) require sealants to function properly in harsh environments at elevated temperatures. The SOFC stacks are expected to experience multiple thermal cycles (perhaps thousands of cycles for some applications) during their lifetime service in stationary or transportation applications. As a result, thermal cycle stability is considered a top priority for SOFC sealant development. In previous work, we have developed a hybrid mica-based compressive seal with very low leak rates of 2–4 × 10⁻² to 10⁻³ sccm cm⁻¹ at 800 °C, and showed stable leak rates over limited thermal cycles. In this paper we present results of long-term thermal cycle testing (>1000 thermal cycles) of Phlogopite mica-based compressive seals. Open-circuit voltage (OCV) was measured on a 2 in. × 2 in. 8-YSZ plate with the hybrid Phlogopite mica seals during thermal cycling in a dual environment (2.75% H₂/Ar versus air). During two long-term cycling tests, the measured OCVs were found to be consistent with the calculated Nernst voltages. The hybrid mica seal showed excellent thermal cycle stability over 1000 thermal cycles and can be considered a strong candidate for SOFC applications.     

Impact of air ions on mass transfer from liquids

Evaporation rates and drying times of liquids exposed to relatively high fluxes of unipolar air ions of either sign, produced by corona electrodes, were studied with a beta-ray gauge apparatus. Liquids of constant volume, exposed to air ions, dried 1.72 to 4.80 times faster than the corresponding control liquids under the same laboratory conditions. An analysis of the time-transmission curves from the beta-ray gauge showed mass transfer rates of 1.90 × 10⁻³ and 8.5 × 10⁻³ g min⁻¹ for control and treated (2.44 × 10¹² positive ions cm⁻² s⁻¹) water, respectively. Air ions were observed to cause circulatory and vibrational movements in the treated liquids. These movements contributed to the enhancement in the mass transfer rates from organic and inorganic liquids studied. Polarity of the molecules may also determine the rapidity at which a liquid will evaporate when exposed to a high flux of air ions.     

Effect of salt concentration on poly (vinyl chloride)/poly (acrylonitrile) based hybrid polymer electrolytes

Hybrid, solid polymer electrolyte films consisting of poly (vinyl chloride) (PVC), poly (acrylonitrile) (PAN) and, propylene carbonate (PC) with different concentrations of LiClO₄ are prepared by means of a using solvent-casting technique. The structure and complex formation are studied by X-ray diffraction (XRD) and Fourier transform infrared (FTIR) spectroscopy. The temperature dependence of the ionic conductivities of the polymer films is explained in terms of a free volume model. The conductivities of PVC–PAN–LiClO₄–PC complexes are determined at different salt concentrations. The highest ionic conductivity (8.35 × 10⁻⁵ S cm⁻¹) is obtained for 8 wt.% LiClO₄ in the polymer complex at 304 K. The thermal stability of the electrolyte is examined by thermogravimetric/differential thermal analysis (TG/DTA).     

Effect of substituting Mm with La on the electrochemical performances of Co-free LaxMm1−x(NiMnSiAlFe)4.9 (x = 0–1) electrode alloys prepared by casting and rapid quenching

In order to enhance the electrochemical capacity of the Co-free AB₅-type electrode alloy, Mm in the alloys was substituted with La and Co-free La_xMm_1−x(NiMnSiAlFe)_4.9 (x = 0, 0.45, 0.75, 1.0) hydrogen storage alloys were prepared by casting and rapid quenching. The effects of the substituting Mm with La on the electrochemical performances of the as-cast and quenched alloys were investigated in detail. The obtained results show that substituting Mm with La can enhance markedly the capacities of the as-cast and quenched alloys. When the amount of substituting Mm with La, x increased from 0 to 1.0, the maximum capacity of the as-cast alloys at 0.2C rate increased from 273.45 to 304.47 mAh g⁻¹, and the capacity retaining rate (R_h) increased from 59.16 to 59.86%. The capacity of the as-quenched alloys with a quenching rate of 10 m s⁻¹ increased from 236.83 to 300.31 mAh g⁻¹, and the capacity retaining rate (R_h) decreased from 78.69 to 62.29%. The substituting Mm with La had an insignificant effect on the activation capabilities of the as-cast and quenched alloys.     

Electrochemical and structural characteristics of niobium(V) oxide in a rechargeable lithium battery

The discharge behaviour of T-Nb₂O₅ in various electrolytes is unaffected by the choice of solvent, but is strongly dependent on the crystal radius of the solute cation species. Thermodynamic and structural studies show that this is due to the insertion of unsolvated Li⁺ ions into the crystal lattice. The graphite content of the Nb₂O₅ electrode has a marked influence on the cycling behaviour on account of the decrease in the oxide conductivity with discharge. Furthermore, the chemical diffusion coefficient of Li⁺ ions in Nb₂O₅ is about 10⁻¹⁰ cm² s⁻¹, which is one order of magnitude smaller than that in V₂O₅ with a layered structure.     

Brown coloring electrochromic devices based on NiO–TiO2 layers

Brown coloring electrochromic 5×10 cm² windows with the configuration K-glass/NiO–TiO₂/electrolyte/CeO₂–TiO₂/K-glass have been prepared and characterized by optoelectrochemical techniques (cyclic voltammetry, chronoamperometry and galvanostatic measurements). The electrochromic layers have been prepared by the sol–gel technique. As electrolyte either a 1 M aqueous KOH solution or a newly developed starch-based gel impregnated with KOH have been used. The CeO₂–TiO₂ sol–gel layers sintered at 550 °C have been previously characterized in 1 M aqueous KOH electrolyte as a function of the thickness up to 2000 cycles and showed a highly reversible behavior without any corrosion effect. The NiO–TiO₂ sol–gel layers sintered at 300 °C have been extensively characterized in the same electrolyte up to about 7000 cycles. All windows present a deep brown color characteristic of the presence of Ni³⁺ (NiOOH) species, that is fully reversible for several thousands of cycles with a rather-fast kinetics (<30 s). The transmittance of the bleached state however slowly decreases with cycling (permanent coloration). The full-bleached condition can be nevertheless recovered by applying a negative potential for a long duration. Deeper coloration is usually obtained by cycling the windows galvanostatically with a current density of 20 μA/cm². The lifetime of the windows is however limited because of the degradation of the NiO-based layers due to the not fully reversible exchange of OH⁻ that turns the layers mechanically fragile and leads eventually to their complete removal from the substrate. Windows working satisfactorily up to 7000 and 17 000 cycles have been obtained using aqueous KOH electrolyte and starch KOH gel electrolyte, respectively. Memory tests showed that the devices bleach at the open circuit potential from T=39% (colored state) to about T=50% in 60 min.     

Electrochemical characteristics and cycle performance of LiMn2O4/a-Si microbattery

A LiMn₂O₄ thin film and an amorphous Si (a-Si) thin film were prepared by radio-frequency (rf) magnetron sputtering. Each thin film was electrochemically evaluated by cyclic voltammetry (CV) and galvanostatic cycling. The rate of capacity fade on cycling was monitored as a function of the voltage window and current density. This was compared with the cycle performance of cathode and anode using two kinds of electrolyte, 1 M LiPF₆ in EC/DMC and PC, for 100 cycles. It was found that the discharge capacity of optimized LiMn₂O₄/a-Si full-cell reached 24 μAh/(cm²-μm) in the first cycle, and a reversible capacity of about 16 μAh/(cm² μm) was still maintained after 100 cycles. In a voltage window of 3.0–4.2 V, LiMn₂O₄/a-Si full-cell exhibits relatively stable cycle performance compared to a voltage window of 2.75–4.2 V.     

Strain controlled LCF behaviour of SA-333 Gr 6 piping material in the range 298–673 K

The low cycle fatigue (LCF) behaviour of carbon steel SA-333 Gr 6 alloy has been investigated between 300 and 673 K employing a triangular waveform at a strain rate of 5×10⁻³ s⁻¹. The cyclic stress response varied as a complex function of temperature. Dynamic strain ageing (DSA) was found to occur over a temperature range between 473 and 623 K. In this DSA domain, the alloy exhibited marked cyclic hardening with a pronounced maximum at 623 K. Additionally the alloy displayed negative strain rate sensitivity of cyclic stress in the DSA regime. The temperature dependence of LCF life showed a maximum at 523 K. The drastic reduction in life between 523 and 673 K has been ascribed primarily to the deleterious effects of DSA on crack initiation and propagation, while the lower life at temperatures less than 523 K has been attributed to the larger cyclic response stress. The influences of DSA on strain–life relationships, cyclic stress–strain curves and fracture behaviour are discussed.     

Singlet methylene removal by saturated and unsaturated hydrocarbons

The technique of laser flash phyotolysis/laser absorption has been used to obtain absolute removal rate constants for singlet methylene, ¹CH₂ (ã¹A₁), with various saturated and unsaturated hydrocarbons. The removal rate constants for CH₄, C₂H₆, C₃H₈, C₂H₄, C₃H₆, C₂H₂, CH₂CCH₂, and C₆H₆ were found to be in excellent agreement with previously reported results. Removal rate constants were also measured for n-C₄H₁₀, i-C₄H₁₀, n-C₅H₁₂, c-C₃H₆, c-C₆H₁₂, 1-C₄H₈, cis-2-C₄H₈, trans-2-C₄H₈, and 1-C₄H₆, and determined to be (3.17 ± 0.15), (2.53 ± 0.11), (3.35 ± 0.24), (1.63 ± 0.08), (3.77 ± 0.21), (3.80 ± 0.20), (3.67 ± 0.16), (3.43 ± 0.16) and (4.05 ± 0.18) × 10⁻¹⁰ cm³ molecule⁻¹ s⁻¹, respectively. This series of hydrocarbons forms the basis of a larger series of compounds containing a wide variety of organic functional groups. The removal rate constants are reported here, both as a series within its own right, and as a reference point for future work.