On the reversibility of hydrogen storage in Ti- and Nb-catalyzed Ca(BH4)2

The hydrogen sorption properties of calcium borohydride (Ca(BH₄)₂) catalyzed with a small amount of TiF₃, TiCl₃, NbF₅ or NbCl₅ are investigated using thermal analyses and X-ray diffraction. NbF₅ exhibits the best performance among all the catalysts; it causes a decrease in the hydrogen desorption temperature which leads to hydrogen absorption at practical temperature and pressure conditions. The hydrogen content of Ca(BH₄)₂ with NbF₅ reaches about 5.0 wt.% after hydrogen absorption at 693 K for 24 h under 90 bar of hydrogen. The main dehydrogenation product of Ca(BH₄)₂ with NbF₅ is a CaH_2−xF_x solid solution with a CaF₂ (C1) structure, while pure Ca(BH₄)₂ produces CaH₂ after hydrogen desorption.     

The effect of doping rare-earth chloride dopant on the dehydrogenation properties of NaAlH4 and its catalytic mechanism

A series of rare-earth chlorides has been adopted to catalyze dehydrogenation reaction of NaAlH₄. X-ray diffraction analysis and isothermal dehydrogenation measurement have proved that these chlorides enhance the dehydrogenation kinetics and lower the decomposition temperature of NaAlH₄. The catalytic effect from high to low is in following order: SmCl₃>CeCl₃>TiCl₃>NdCl₃>GdCl₃>LaCl₃>ErCl₃. In order to reveal the catalytic mechanism of the rare-earth chlorides on dehydrogenation reactions, systems doped with LaCl₃ were investigated under different milling and dehydrogenation conditions. It has been proposed that the La cation reacts with hydrogen, which was released from NaAlH₄, and then forms some sort of La–Al alloys. This process improves the performance of NaAlH₄ dehydrogenation at a relatively low temperature. In the present research, the catalytic effect of La₂O₃ has also been investigated. Results show that La₂O₃ also have a catalytic effect on the dehydrogenation of NaAlH₄, but the effect is less obvious than that of the rare-earth chlorides.     

Production of hydrogen gas from novel chemical hydrides

Six ligand-stabilized complexes have been synthesized and tested for use as hydrogen storage media for portable fuel cell applications. The new hydrides are: [HC(3,5-Me₂pz)₃]LiBH₄ (1), {[H₂C(3,5-Me₂pz)₂]Li(BH₄)}₂ (2) (pz = pyrazolyl), [(TMEDA)Li(BH₄)]₂ (3) (TMEDA = (CH₃)₂NCH₂CH₂N(CH₃)₂), [HC(pz)₃]LiBH₄ (4), {[H₂C(pz)₂]Li(BH₄)}₂ (5) and Mg(BH₄)^.₂ 3THF (6) (THF = tetrahydrofuran). Hydrolysis reactions of the compounds liberate hydrogen in quantities which range from 56 to 104 (± 5%) percent of the theoretical yield. Gas chromatographic analysis of the product gases from these reactions indicate that hydrogen is the only gas produced. Thermally initiated reactions of the novel compounds with NH₄Cl were unsuccessful. Although the amount of hydrogen energy which can be theoretically obtained per unit weight is lower than that of the classical hydrides such as LiBH₄ and NaBH₄, the reactions are less violent and hydrolysis of compounds 1, 2, 4, 5 and 6 releases less heat per mole of hydrogen generated.     

石墨烯包封Na3V2(PO4)3用作钠离子电池负极材料的电化学性能探究

具有三维网络结构的NASICON型Na₃V₂(PO₄)₃材料,由于其稳定的电压平台,较高的理论容量(117 mA·h/g),被视为一种具有良好应用前景的钠离子电池负极材料。采用溶剂热和进一步热处理的方式,获得石墨烯包封Na₃V₂(PO₄)₃的复合材料[Na₃V₂(PO₄)₃/G],有效提高了Na₃V₂(PO₄)₃的电子导电性。在0.01～3.00 V电压区间,0.2 C倍率进行测试时,Na₃V₂(PO₄)₃/G复合材料在230圈循环后,其放电比容量保持在100.9 mA·h/g,容量保持率高达68.4%,即使在5 C倍率,其放电比容量仍可达65.2 mA...     

Molecular dynamics simulations on the effect of temperature and loading in H2 exohedral adsorption on and SWCNTs

The adsorption of H₂ on single walled carbon nanotubes is investigated as a function of temperature, H₂ loading and diameter of the nanotubes. The physisorption phenomenon is simulated by extensive equilibrium molecular dynamics. The applied intermolecular forces are modeled using the modified form of the well-known Lennard-Jones potential based on the tube curvature. The simulation results of exposing different H₂ loadings on (3,3) and (9,9), at 77,300 and 600 K, under moderate pressure of 10 bar, show that the amount of adsorption is strongly influenced by the applied temperature, and that the adsorption energy is higher for nanotubes with smaller diameters. Moreover, analyzing the deformation of the nanotube adsorbents during the simulation time indicates that increasing the operating temperatures not only decreases the amount of adsorption monotonically but also imposes more nanotube distortions.     

Steam and auto-thermal reforming of bio-ethanol over MgO and Ni supported catalysts

Ethanol reforming over MgO and CeO₂ Ni supported catalysts in molten carbonate fuel cell (MCFC) simulated operative conditions has been investigated. Results revealed that an optimum O₂/C ratio (ATR condition) exists to enhance the performance of both catalysts which otherwise significantly deactivate mainly due to the coke formation. Oxygen contributes to depress coke formation but in some cases promotes acetaldehyde formation specially on Ni/CeO₂ catalysts. Very high H₂ selectivity (>98%) in steam reforming (SR) were obtained on both Ni/MgO and Ni/CeO₂ catalysts by operating at while in ATR conditions a decrease in hydrogen selectivity was observed at high GHSV only since reactions involved in the reaction mechanism are not at equilibrium.     

Development of the integrated methanol fuel processor using micro-channel patterned devices and its performance for steam reforming of methanol

A plate-type integrated fuel processor consisting of three different micro-structured modules was developed for hydrogen production in a 150 W PEMFC system. This system includes a reformer with combustor, two heat exchangers, and an evaporator with a combustor. Methanol steam reforming was chosen as a means to produce hydrogen for the PEMFC system. This system could be operated without any external heat supply. Hydrogen was used as the initial combustion fuel during startup, while methanol was used later. Cu/Zn/Al₂O₃ and Pt/Al₂O₃ catalysts were chosen for the steam reforming of methanol and the combustion, respectively, and coated on microchannel-patterned stainless steel sheets.

The integrated system was operated consistently with 80% of methanol conversion at for 20 h without deactivation of the catalysts. The production rate on dry basis and the composition of hydrogen was and ca 70%, respectively. Overall the thermal efficiency of this fuel processor based on the LHV was 56.7%.     

Thermochemical two-step water-splitting reactor with internally circulating fluidized bed for thermal reduction of ferrite particles

A thermochemical two-step water-splitting cycle using a redox system of iron-based oxides or ferrites was examined on hydrogen productivity and reactivity of ferrite in order to convert solar energy into hydrogen in sunbelt regions. In the present paper, a new concept is proposed for a windowed thermochemical water-splitting reactor, using an internally circulating fluidized bed of NiFe₂O₄/m-ZrO₂ particles, and thermal reduction of the bed is demonstrated on a laboratory scale by using a solar-simulating Xe-beam irradiation. The concept is that concentrated solar radiation passes through the transparent window and directly heats the internally circulating fluidized bed. The fluidized bed reactor enabled the NiFe₂O₄/m-ZrO₂ sample to remain in powder form without sintering and agglomerating during direct Xe-beam irradiation over 30 min. Approximately 45% of the NiFe₂O₄ was converted to the reduced phase by the solar-simulated high-flux beam, and was then completely reoxidized with steam at 1000 °C to generate hydrogen.     

Photoelectrocatalytic generation of H2 and S from toxic H2S by using a novel BiOI/WO3 nanoflake array photoanode

In this paper, a photoelectrocatalytic (PEC) recovery of toxic H₂S into H₂ and S system was proposed using a novel bismuth oxyiodide (BiOI)/ tungsten trioxide (WO₃) nano-flake arrays (NFA) photoanode. The BiOI/WO₃ NFA with a vertically aligned nanostructure were uniformly prepared on the conductive substrate via transformation of tungstate following an impregnating hydroxylation of BiI₃. Compared to pure WO₃ NFA, the BiOI/WO₃ NFA promotes a significant increase of photocurrent by 200%. Owing to the excellent stability and photoactivity of the BiOI/WO₃ NFA photoanode and I^–/{\mathrm{I}}_{\mathrm{3}}^{-} catalytic system, the PEC system toward splitting of H₂S totally converted S^2– into S without any polysulfide ({\mathrm{S}}_x^{n-}) under solar-light irradiation. Moreover, H₂ was simultaneously generated at a rate of about 0.867 mL/(h·cm). The proposed PEC H₂S splitting system provides an efficient and sustainable route to recover H₂ and S.     

Behavior of the monophosphate tungsten bronzes (PO2)4(WO3)2m (m = 4 and 6) in electrochemical lithium insertion

The electrochemical lithium insertion process has been studied in the family of monophosphate tungsten bronzes (PO₂)₄(WO₃)_2m, where m = 4 and 6. Structural changes in the pristine oxides were followed as lithium insertion proceeded. Through potentiostatic intermittent technique, the different processes which take place in the cathode during the discharge of the cell were analysed. The nature of the bronzes Li_x(PO₂)₄(WO₃)_2m formed was determined by in situ X-ray diffraction experiments. These results have allowed establishment of a correlation with the reversible/irreversible processes detected during the electrochemical lithium insertion. Measurements of resistivity showed that upon lithium insertion, the metallic pristine oxides become insulating.     

Defect reduction in electrochemically deposited CdS thin films by annealing in 02

Using the electrochemical deposition method, CdS thin films were deposited from acid solutions (pH = 2.5) containing CdS0₄ and Na₂S₂0₃ on indium-oxide coated glass substrates. These films were annealed in N₂, air, or O₂ atmosphere at 200–500°C for 30 min. Photoluminescence spectra were measured at 77 K. For the films annealed in N₂, the band edge emission became weaker and the luminescence due to defects shifted to longer wavelengths as the annealing temperature was raised above 300°C. However, for the films annealed in air or O₂, the band edge emission was observed strongly irrespective of the annealing temperature and the luminescence due to defects was weak. Thus the O₂ annealing is useful for the defects reduction.     

A highly active catalyst, Ni/Ce–ZrO2/θ-Al2O3, for on-site H2 generation by steam methane reforming: pretreatment effect

The steam treatment effect has been investigated over the doubly impregnated catalyst, Ni/Ce–ZrO₂/θ-Al₂O₃, in steam methane reforming (SMR). The catalyst was remarkably deactivated by steam treatment but reversibly regenerated by H₂-reduction. XRD results showed that the steam treatment resulted in the formation of NiAl₂O₄ which is inactive for SMR but it was reversibly converted to Ni by the reduction. The reversible oxidation-reduction of Ni state was also evidenced by XPS and it was observed that the formation of NiAl₂O₄ is more favorable at higher temperature. It is most likely that the alumina support is only partially covered with Ce–ZrO₂ and most Ni directly interacts with θ-Al₂O₃ which would probably make easy formation of NiAl₂O₄ in the presence of steam alone. The results imply that, during the start-up procedure in SMR, too high concentration of steam could deactivate seriously Al₂O₃ supported Ni catalysts.     

Mo2C/Al2O3的制备及其催化二甲醚水蒸气重整性能研究

通过浸渍沉淀法结合程序升温碳化法制备了Mo₂C/Al₂O₃复合催化剂,并应用于二甲醚水蒸气重整催化体系的研究。考察了二甲醚水解催化载体、水解功能组分Al₂O₃与重整功能组分Mo₂C的比例、反应物浓度对复合催化剂活性的影响。结果表明,β-Mo₂C与γ-Al₂O₃载体以Mo/Al = 1/1耦合后能够高效催化二甲醚重整制氢,其最佳进料水醚比为5,最适反应温度为400℃。     

MW-assisted synthesis of LiFePO4 for high power applications

LiFePO₄/C was prepared by solid-state reaction from Li₃PO₄, Fe₃(PO₄)₂·8H₂O, carbon and glucose in a few minutes in a scientific MW (microwave) oven with temperature and power control. The material was characterized by X-ray diffraction, scanning electron microscopy and by TGA analysis to evaluate carbon content. The electrochemical characterization as positive electrode in EC (ethylene carbonate)–DMC (dimethylcarbonate) 1 M LiPF₆ was performed by galvanostatic charge–discharge cycles at C/10 to evaluate specific capacity and by sequences of 10 s discharge–charge pulses, at different high C-rates (5–45C) to evaluate pulse-specific power in simulate operative conditions for full-HEV application. The maximum pulse-specific power and, particularly, pulse efficiency values are quite high and make MW synthesis a very promising route for mass production of LiFePO₄/C for full-HEV batteries at low energy costs.     

Feasibility study on bioreactor strategies for enhanced photohydrogen production from Rhodopseudomonas palustris WP3-5 using optical-fiber-assisted illumination systems

A novel photobioreactor (PBR) was utilized to produce H₂ by indigenous purple nonsulfur bacterium Rhodopseudomonas palustris WP3-5 using acetate as the sole carbon source. The PBR was illuminated by combinative light sources including side-light optical fibers (internal light source) as well as external irradiation of halogen lamp and/or tungsten filament lamp. A fill and draw (F/D) operation of PBR was shown to improve the performance of photoH₂ production over the performance of batch and continuous cultures under similar operation conditions. For medium improvement, the PBR was conducted under different concentrations of carbon source (acetate) and nitrogen source (glutamic acid). The results show that the highest overall H₂ production rate (v_H2) and H₂ yield (Y_H2) occurred when the acetate concentration was 32.5 mmol/l and the glutamic acid concentration was 400 mg/l. The optimal acetate and glutamic acid concentration led to a v_H2 and Y_H2 of 20.9 ml/h l and 2.47 mol H₂/mol acetate, respectively. The H₂ production rate and yield was further enhanced to as high as 38.2 ml/h l and 3.15 mol H₂/mol acetate, respectively, while using a ternary-light-source (TLS) system, combining optical fiber, halogen lamp, and tungsten filament lamp (i.e., the OF/HL/TL system). Meanwhile, the high H₂ production efficiency with TLS system was stably maintained for nearly 30 day under the F/D operations.     

Characterization of Cu(InxGa1−x)2Se3.5 thin films prepared by rf sputtering

Cu(In_xGa_1−x)₂Se_3.5 thin films were fabricated by rf sputtering from CuIn_xGa_1−xSe₂ and Na mixture target by controlling the mixture ratio. X-ray diffraction analyses show that the structure of Cu(In_xGa_1−x)₂Se_3.5, thin films is different from chalcopyrite structure: especially, CuIn₂Se_3.5 thin films have a defect chalcopyrite structure. The lattice parameters for Cu(In_xGa_1−x)₂Se_3.5 thin film are slightly smaller than those for CuIn_xGa_1−xSe₂ thin film and linearly decreased with increasing Ga content. The optical absorption coefficients for Cu(In_xGa_1−x)₂Se_3.5, thin films exceed 2 × 10⁴ cm⁻¹ in energy region above the fundamental band edge. The band gap for Cu(In_xGa_1−x)₂Se_3.5 thin films is larger than that for CuIn.Ga_1−x2Se₂ with the same Ga content and increased with increasing Ga content.     

The electrochemical properties of /polyaniline composites

The La_0.7Mg_0.25Ti_0.05Ni_2.975Co_0.525 (AB₃) alloy was modified with different contents of polyaniline (PANI) through ball milling. XRD, SEM and FTIR were used to characterize the properties of the AB₃/x PANI composites (x=1, 2, 3 and 4 wt%). The effects of PANI on the electrochemical properties of AB₃ alloy electrode were studied by charge–discharge, electrochemical impedance spectroscopy (EIS), linear polarization (LP) and potentiostatic discharge experiments. The XRD, SEM and FTIR results showed that ball milling did not change the characterizations of PANI and AB₃ alloy but decreased the average particle size of AB₃ alloy. The charge–discharge results indicated that the maximum discharge capacity of AB₃ alloy electrode decreased with the addition of PANI. However, the discharge cycle stability of AB₃/PANI composite electrodes increased firstly and then decreased with the increase in PANI content. The EIS and LP curves showed the same trends with the discharge cycle stability. The hydrogen diffusion coefficients of AB₃/PANI composites were estimated from the potentiostatic discharge curves, indicated the opposite trend with the discharge cycle stability. When the PANI content was equal to 3 wt%, the AB₃/PANI composite electrode exhibited an optimal electrochemical kinetic property.     

Characteristics of a phototrophic sludge producing hydrogen from acetate and butyrate

A mixed phototrophic sludge was enriched from the sediment of a local river for continuous hydrogen production from acetate and butyrate in a complete-mix reactor. At pH 7.0–7.5 and , the optimal hydrogen production rate at 48 h of hydraulic retention time (HRT) for 150 days of steady-state operation averaged with of biomass. The sludge yield averaged -VSS/g-COD. Results of batch experiments showed an optimal pH of 8.5 and an optimal concentration of 2 mM for hydrogen production. At 10 mM, severely inhibited the hydrogen production. Three of the five OTUs classified from 26 clones developed from the seed sludge were phototrophs, based on phylogenetic analysis. Among them, OTU LA15, which is closely related to Rhodobacter sp., was most likely responsible to the hydrogen production.     

Preparation and properties of LiCoyMnxNi1−x−yO2 as a cathode for lithium ion batteries

The preparation of LiCo_yMn_xNi_1−x−yO₂ from LiOH·H₂O, Ni(OH)₂ and γ-MnOOH in air was studied in detail. Single-phase LiCo_yMn_xNi_1−x−yO₂ (0y0.3 and x=0.2) is obtained by heating at 830–900°C. The optimum heating temperatures are 850°C for y=0–0.1 and 900°C for y=0.2–0.3. Excess lithium (1z1.11 for y=0.2) and the Co doping level (0.05y0.2) do not significantly affect the discharge capacity of Li_zCo_yMn_0.2Ni_0.8−yO₂. The doping of Co into LiMn_0.2Ni_0.8O₂ accelerates the oxidation of the transition metal ion, and suppresses partial cation mixing. Since the valence of the manganese ion in LiMn_0.2Ni_0.8O₂ is determined to be 4, the formation of a solid solution between LiCo_yNi_1−yO₂ and Li₂MnO₃ is confirmed.     

Energy-efficient conversion of propane to propylene and ethylene over a V2O5/CeO2/SA5205 catalyst in the presence of limited oxygen

Oxidative conversion of propane to propylene and ethylene over a V₂O₅/CeO₂/SA5205 (V:Ce=1:1) catalyst, with or without steam and limited O₂, has been studied at different temperatures (700–850 °C), C₃H₈/O₂ ratio (4.0), H₂O/C₃H₈ ratio (0.5) and space velocity (3000 cm³ g⁻¹ h⁻¹). The propane conversion, selectivity for propylene and net heat of reaction (ΔHr) are strongly influenced by the reaction temperature and presence of steam in the reactant feed. In the presence of steam and limited O₂, the process involves a coupling of endothermic thermal cracking and exothermic oxidative conversion reactions of propane which occur simultaneously. Because of the coupling of exothermic and endothermic reactions, the process operates in an energy-efficient and safe manner. The net heat of reaction can be controlled by the reaction temperature and concentration of O₂. The process exothermicity is found to be reduced drastically with increasing temperature. Due to the addition of steam in the feed, no coke formation was observed in the process.