Synthesis and characterization of , and hydrogen production from methanol photodecomposition over the mixture of and

This study focused on the production of hydrogen from the methanol destruction in a liquid photocatalytic system that comprised a mixture of Ag_xO and TiO₂ (P-25, Degussa). The nanometer particles of Ag_xO were obtained by a conventional sol–gel method in the presence of tetraethylammonium hydroxide using thermal treatment at 50, 100, 150, 200, 250, and to attain various silver oxide forms. The 38.0 and 43.0 peaks, which were assigned to Ag₂O and Ag metal, respectively, were seen in Ag_xO powder at each temperature; however, these Ag₂O/Ag ratios varied and the AgO form was not found in any of the samples. In the XPS data, the peak which was assigned to Ag3d_5/2 in the Ag metal or Ag₂O was present in all the Ag_xO samples. In particular, the peak of Ag3d_5/2 in the Ag metal was dominant at high temperature, while the peak of Ag3d_5/2 in Ag₂O increased at low temperature. When TiO₂ was used as a photocatalyst in the methanol photodecomposition reaction, no hydrogen gases were evolved. However, the hydrogen product was remarkably increased in the mixture of Ag_xO and TiO₂ photo-system. Moreover, it was more enhanced when Ag_xO thermally treated at was added, compared to the samples with Ag_xO thermally treated at other temperatures, and the production peaked at 17,000 μmol after 24 h.     

Spectral Photosensitivity ofpSi—n(ZnSe)1?x?y(Si2)x(GaP)y Structures

Epitaxial layers of substitutional solid solution (ZnSe)_1−x−y(Si₂) _x (GaP) _y (0.1 ≤x≤ 1, 0≤y≤0.9) on pSi substrates were developed from a limited volume of tin solution-melt using the method of a liquid phase epitaxy. The spectral dependency of photosensitivity of the pSi—n(ZnSe)₁ −x−y (Si₂) _x (Ga.P) _y structures was studied and the peaks of photoresponses at energies of photons of 1.6, 1.66, and 1.92 eV at room temperature were discovered. It was shown that the forward-bi as regions of the volt—ampere characteristics of structures under study can be described by the power dependence of −I = I ₀ + B · V ^m with various values of a power index at various values of the voltage applied.     

Photosensitivity of p Si- n (GaSb)1 ? x ? y (Si2) x (GaAs) y , p Si- n (GaSb)1 ? x ? y (Si2) x (GaAs) y ,- n (GaSb) structures

Two-stage buffer n(GaSb)_{1 − x − y} (Si₂) _x (GaAs) _y and perfect n(GaSb) layers are grown on an pSi substrate by liquid-phase epitaxy from a tin solution-melt. It is shown that the photosensitivity of the pSi−n(GaSb)_{1 − x − y} (Si₂) _x (GaAs) _y structures is in the spectral range 1.0-1.6 eV, and that of the pSi − n (GaSb)_{1 − x − y} (Si₂) _x (GaAs) _{y − n} (GaSb) structures is in the range 0.62-1.15 eV. Original Russian Text ? A.S. Saidov, M.S. Saidov, Sh.N. Usmonov, D. Saparov, K.T. Kholikov, 2008, published in Geliotekhnika, 2008, No. 3, pp. 56–58.     

Formation of proposed superconducting phases in nominal compositions Bi1.7Pb0.3Sr2Cax ? 1CuxOy (x = 4, 5, 7, 9) on the basis of amorphous precursors, obtained under the action of concentrated sunlight

The possibility of obtaining superconducting phases in compositions Bi_1.7Pb_0.3Sr₂Ca _{x − 1}Cu _x O _y (x = 4, 5, 7, 9) with increased Ca and Cu content from amorphous precursors that are obtained under the action of concentrated sunlight is investigated. It is established that the temperature of formation of the superconducting phases decreases with increase of the Ca and Cu content.     

Catalytic activities of Ag/C decorated with small amounts of Au and Pt for glycerol oxidation

The two-step decoration of the Ag nanoparticles supported on carbon black (Ag/C) with Au and Pt, the electrooxidation of glycerol on the Pt/Au/Ag/C catalysts in alkaline solution, and the effect of the amounts of Au and Pt on the catalytic activity of Pt/Au/Ag/C are investigated. The decoration of Ag/C is performed by electrochemically depositing a small amount of Au and then Pt on Ag/C, and the Pt_x/Au_y/Ag₁₀₀/C catalysts with different x:y:100 ratios (0.15 ≤ x ≤ 1.9 and 0.2 ≤ y ≤ 1.5) are obtained. Physical and electrochemical characterizations reveal that small parts of the Ag surfaces are covered by the deposited Au and Pt. Pt_x/Au_y/Ag₁₀₀/C mainly shows Pt-relevant behaviors in glycerol oxidation, and Pt_1.3/Au_y/Ag₁₀₀/C exhibits high catalytic activities. The results reveal that the surface decoration is a useful method of fabricating efficient ternary catalysts at low cost.     

Effect of gamma irradiation on photoconductivity and photosensitivity of Si<Subscript>1 − <Emphasis Type="Italic">x</Emphasis></Subscript>Sn<Subscript><Emphasis Type="Italic">x</Emphasis></Subscript> solid solutions

The results of studies of the structural feature and the effect of low-dose gamma irradiation (up to 105 rad) on the photoconductivity relaxation and the spectral photosensitivity of pSi-nSi_{1 − x} Sn _x (0 ≤ x ≤ 0.04) structures are described. It is shown that exposure to radiation leads to an increase in the relaxation time constant from 55 to 83 μs and an enhancement in the sensitivity of the structures in the short-wavelength emission spectrum, which is attributed to the radiation-stimulated gettering of crystal lattice defects localized in the near-boundaries regions between Si_{1 −x} Sn _x subcrystallites and Si_{1 − x} Sn _x -Sn and Si_{1 − x} Sn _x -SiO₂ phases.     

Active solar energy material science thermoelectric properties of nGe-p(InSb)1 ? x(Sn2)x heterostructures

By the method of liquid phase epitaxy, the epitaxial layers of a substitutional solid solution of the (InSb)_{1 − x} (Sn²) _x (1 ≤ x ≤ 0.05) p type of conductivity on nGe substrates were grown from a limited volume of an indium solution melt. It has been found that during the heating of the structure in the dark, an electrical current and voltage are generated in it.     

High-throughput characterization of Ag–V–O nanostructured thin-film materials libraries for photoelectrochemical solar water splitting

Ag–V–O thin-film materials libraries, with both composition (Ag_22-77V_23-78O_x) and thickness (123–714 nm) gradients were fabricated using combinatorial reactive magnetron co-sputtering aiming on establishing relations between composition, structure, and functional properties. As-deposited libraries were annealed in air at 300 °C for 10 h. High-throughput characterization methods of composition, structure and functional properties were used to identify photoelectrochemically active regions. The phases AgV₆O₁₅, Ag₂V₄O₁₁, AgVO₃, and Ag₄V₂O₇ were observed throughout the composition gradient. The photoelectrochemical properties of Ag–V–O films are dependent on composition and morphology. An enhanced photocurrent density (~300–554 μA/cm²) was obtained at 30 to 45 at.% Ag along the thickness gradient. Thin films of these compositions show a nanowire morphology, which is an important factor for the enhancement of photoelectrochemical performance. The photoelectrochemically active regions were further investigated by high-throughput synchrotron-X-ray diffraction and transmission electron microscopy (Ag₃₂V₆₈O_x) which confirmed the presence of Ag₂V₄O₁₁ as the dominating phase along with the minor phases AgV₆O₁₅ and AgVO₃. This enhanced photoactive region shows bandgap values of ~2.30 eV for the direct and ~1.87 eV for the indirect bandgap energies. The porous nanostructured films improve charge transport and are hence of interest for photoelectrochemical water splitting.     

Photoluminescence studies of p-type chalcopyrite AgInS2:Sn

Chalcopyrite AgInS₂:Sn thin films were prepared by spray pyrolysis technique for a constant ratio of [Ag]/[In]=1.5 and different SnCl₄ concentrations (0.05, 0.1 and 0.2 ml) in the spray solution obtaining x=[SnCl₄]/[Ag]+[In]=0.01, 0.02, 0.04. All films were deposited at substrate temperature of 375 °C. The deposited film for which x=0.02 exhibited p-type conductivity, having band-gap energies of 1.87 and 2.01 eV. Photoluminescence (PL) studies reveal several PL bands located at 1.45, 1.68, 1.70, 1.80 and 1.88 eV at 10 K. Each one of these PL structures are related to different defects, the 1.45 eV emission is related to indium vacancies, 1.80 eV emission to interstitial silver (Ag_in) or Indium in sites of silver (Ag_In), whereas, the other emissions (1.70 and 1.88 eV) are related with a donor–acceptor pair recombination and free to bound transition, respectively, due to sulphur vacancies. Sn in excess modifies the emission bands located at 1.70 and 1.88 eV; we found that Sn reduces sulphur vacancies and PL spectra are dominated by acceptor impurities.     

First-principles studies of the structures and properties of Al- and Ag-substituted Mg2Ni alloys and their hydrides

The structures and properties of hydrogen storage alloy Mg₂Ni, of aluminum and silver substituted alloys Mg_2−xM_xNi (M = Al and Ag, x = 0.16667), and of their hydrides Mg₂NiH₄, Mg_2−xM_xNiH₄ (M = Al and Ag, x = 0.125) have been calculated from first-principles. Results show that the primitive cell sizes of the intermetallic alloys and hydrides were reduced by substitution of Mg with Al or Ag. Also, the interaction of Ni–Ni was weakened by the substitution. A strong covalent interaction between H and Ni atoms forms tetrahedral NiH₄ units in Mg₂NiH₄. The NiH₄ unit near the Al/Ag atom became tripod-like NiH₃ in Mg_2−xM_xNiH₄ (M = Al, Ag), indicating that the hydrogen storage capacity was decreased by the substitution. The calculated enthalpies of hydrogenation for Mg₂Ni, Mg_2−xAl_xNi and Mg_2−xAg_xNi are −65.14, −51.56 and −53.63 kJ/mol H₂, respectively, implying that the substitution destabilizes the hydrides. Therefore, the substitution is an effective technique for improving the thermodynamic behavior of hydrogenation/dehydrogenation in magnesium-based hydrogen storage materials.     

Evaluation of structural,electronic, thermoelectric,and optical results of C-doped HfO2 by first-principle's investigation

In this work, we report the ab initio numerical simulation investigation on the crystal lattice, electronic structure, optical, and transport properties of pure and C-doped crystalline hafnium dioxide (c-HfO₂) using FP-LAPW method. Different exchange correlation functionals like generalized gradient approximation (GGA) of PBE-sol and Tran and Blaha's modified Becke-Johnson exchange potential (mBJ) within density functional theory have been used. Two kinds of defects in cubic pure HfO₂ have been investigated: one is substitution of Hf atom by C impurity and other substitution of O atom by C impurity in crystalline HfO₂. The computed results indicate that impurity energy bands as a result of 2p states of C are found to present in the band gap of c-HfO₂. Few of these bands are present at the conduction band minimum, which results to a noteworthy band gap contraction, and hence electrons close to Fermi level get transferred in doped c-HfO₂. We have also analysed the dielectric function, absorption coefficient, optical conductivity, optical function, electron energy loss, and reflectivity for both pure HfO₂ and doped with C. Furthermore, the temperature-dependent transport properties of C-doped HfO₂ are also discussed in terms of Seeback coefficient, thermal conductivities, electronic conductivities, power factor, and figure of merit in the temperature range 0 to 1200 K. The calculated value of PF for pure HfO₂ was found to increase from 0.01 × 10¹² WK⁻²m⁻¹s⁻¹ at 50 K to 1.79 × 10¹² WK⁻²m⁻¹s⁻¹ at 1200 K and for HfO_{2(1 − x)}C_x it was found to increase from 0.06 × 10¹² WK⁻²m⁻¹s⁻¹ at 50 K to 0.25 × 10¹² WK⁻²m⁻¹s⁻¹ at 1200 K.     

Principal Poincaré–Pontryagin Function of Polynomial Perturbations of the Hamiltonian Triangle

In this paper, we consider a small polynomial perturbation of the Hamiltonian vector field with the Hamiltonian F(x, y) = x[y² − (x − 3)²] having a center bounded by a triangle. The main result of this work is that the principal Poincaré–Pontryagin function associated with such a perturbation and with the family of ovals surrounding the center belongs to the ℂ[t, 1/t] module generated by Abelian integrals I₀(t) and I₂(t) and by I*(t), where I*(t) is not an Abelian integral. We show that, in general, the principal Poincaré–Pontryagin function of order two of a polynomial perturbation of the degree at least five is not an Abelian integral. 2000 Mathematics Subject Classification. 34M35; 34C08; 14D05.     

Mechanism for the formation of Ag crystallites in the Ag thick-film contacts of crystalline Si solar cells

This study examined the interfacial reactions between various Ag pastes and (100) Si wafers with and without an SiN_x layer during firing at 800 °C for extended times in order to better understand the mechanism for the formation of Ag crystallites in Ag thick-film contacts of crystalline Si solar cells. The results showed that, in contrast to the model proposed previously, the Ag crystallites were formed by a direct reaction between Ag⁺ ions dissolved in the glass frit and the Si wafer without an aid of liquid-Pb formation. The redox reactions between PbO and Si as well as between PbO and SiN_x were suppressed by adding a few weight percent of Ag powder into the glass frit. The size and distribution of the inverted pyramidal Ag crystallites formed at the glass/Si interface were found to depend critically on the PbO content in the glass frit. The role of PbO in Ag crystallite formation was discussed in terms of the solubility of Ag and the viscosity of the glass frit at the firing temperature.     

The composition dependence of the effective thickness of the base layer in Al<Subscript><Emphasis Type="Italic">x</Emphasis></Subscript>Ga<Subscript>1 − <Emphasis Type="Italic">x</Emphasis></Subscript>P/GaP heterophotoconverters

The dependence between the composition of Al _x Ga_{1 − x} P heterophotoconverters and the effective thickness of their base layers was established. An empirical formula to estimate the effective thickness of a base layer as a function of the composition of solid-state solution (0 ≤ x ≤ 0.8) was proposed.     

Structure and hydrogen storage properties of Mg2Cu1−xNix (x = 0–1) alloys

The effect of Ni-substitution on the structure and hydrogen storage properties of Mg₂Cu_1−xNi_x (x = 0, 0.2, 0.4, 0.6, 0.8, 1) alloys prepared by a method combining electric resistance melting with isothermal evaporation casting process (IECP) has been studied. The X-ray single-crystal diffraction analysis results showed that the cell volume decreases with increasing Ni concentration, and crystal structure transforms Mg₂Cu with face-centered orthorhombic into Ni-containing alloys with hexagonal structure. The Ni-substitution effects on the hydriding reaction indicated that absorption kinetics and hydrogen storage capacity increase in proportion to the concentration of the substitutional Ni. The activated Mg₂Cu and Mg₂Ni alloys absorbed 2.54 and 3.58 wt% H, respectively, at 573 K under 50 bar H₂. After a combined high temperature and pressure activation cycle, the charged samples were composed of MgH₂, MgCu₂ and Mg₂NiH₄ while the discharged samples contained ternary alloys of Mg–Cu–Ni system with the helpful effect of rising the desorption plateau pressures compared with binary Mg–Cu and Mg–Ni alloys. With increasing nickel content, the effect of Ni is actually effective in MgH₂ and Mg₂NiH₄ destabilization, leading to a decrease of the desorption temperature of these two phases.     

Fiber-based flexible thermoelectric power generator

Flexible thermoelectric power generators fabricated by evaporating thin films on flexible fiber substrates are demonstrated to be feasible candidates for waste heat recovery. An open circuit voltage of 19.6 μV K per thermocouple junction is measured for Ni–Ag thin films, and a maximum power of 2 nW for 7 couples at ΔT = 6.6 K is measured. Heat transfer analysis is used to project performance for several other material systems, with a predicted power output of 1 μW per couple for Bi₂Te₃/Sb₂Te₃-based fiber coatings with a hot junction temperature of 100 °C. Considering the performance of woven thermoelectric cloths or fiber composites, relevant properties and dimensions of individual thermoelectric fibers are optimized.     

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.     

Effect of Mg3MnNi2 on the electrochemical characteristics of Mg2Ni electrode alloy

Mg₂Ni–x mol% Mg₃MnNi₂ (x = 0, 15, 30, 60, 100), the novel composite alloys employed for hydrogen storage electrode, have been successfully synthesized by a method combining electric resistance melting with isothermal evaporation casting process (IECP). X-ray diffraction (XRD) analysis results show that the composite alloys are composed of Mg₂Ni phases and the new Mg₃MnNi₂ phases. It is found on the electrochemical studies that maximum discharge capacities of the composite alloys increase with the increasing content of the Mg₃MnNi₂ phase. The discharge capacity of the electrode alloy is effectively improved from 17 mAh g⁻¹ of the Mg₂Ni alloy to 166 mAh g⁻¹ of the Mg₃MnNi₂ alloy. Among these alloys, the Mg₃MnNi₂ phase possesses a positive effect on the retardation of cycling capacity degradation rate of the electrode materials. Cyclic voltammetry (CV) results confirm that the increasing content of the Mg₃MnNi₂ phase effectively improves the reaction activity of the electrode alloys. Surface analyses indicate that the Mg₃MnNi₂ phase can enhance the anti-corrosive performance of the particle surface of these composite alloys.     

Control of homogeneous charge compression ignition combustion in a two-cylinder gasoline direct injection engine with negative valve overlap

Homogeneous charge compression ignition (HCCI) has challenges in ignition timing control, combustion rate control, and operating range extension. In this paper, HCCI combustion was studied in a two-cylinder gasoline direct injection (GDI) engine with negative valve overlap (NVO). A two-stage gasoline direct injection strategy combined with negative valve overlap was used to control mixture formation and combustion. The gasoline engine could be operated in HCCI combustion mode at a speed range of 800–2 200 r/min and load, indicated mean effective pressure (IMEP) range of 0.1–0.53 MPa. The engine fuel consumption is below 240 g/(kW⁻¹·h⁻¹), and the NO _x emission is below 4 × 10⁻⁵ without soot emission. The effect of different injection strategies on HCCI combustion was studied. The experimental results indicated that the coefficient of variation of the engine cycle decreased by using NVO with two-stage direct injection; the ignition timing and combustion rate could be controlled; and the operational range of HCCI combustion could be extended. Translated from J Tsinghua Univ (Sci & Tech), 2006, 46(5): 720–723 [译自: 清华大学学报]     

Easy sintering of silver doped lanthanum strontium manganite current collector for solid oxide fuel cells

A new system, (La_0.8Sr_0.2)_1−xAg_xMnO_3+δ (LSAM, x ≤ 0.2), is developed as current collector for solid oxide fuel cell (SOFC). LSAM is prepared by a modified sol-gel method and presents a single phase. The shrinkage temperature reduces from 1150 °C to 800 °C with an addition of 15 mol% Ag to La_0.8Sr_0.2MnO_3+δ (LSM20). The contact resistance between the current collector and the cathode is measured, and the influence of Ag content on the contact resistance is investigated. The result shows that the contact resistance using (La_0.8Sr_0.2)_0.85Ag_0.15MnO_3+δ (LSAM15) as current collector is about 12 mΩ cm² at 750 °C, which is close to the value using expensive Pt paste as current collector. This new system is a promising current collecting material for the practical application of SOFC.