Improved hydrogen generation from alkaline solution using carbon-supported as catalysts

Carbon-supported Co–B catalysts with various loading contents were prepared by impregnation–chemical reduction method. The XRD, ICP, SEM and TEM analyses revealed that the as-prepared Co–B catalysts were in amorphous form with the composition of Co_2.0–3.3B and the carbon-supported Co–B catalysts had a good dispersion and coating condition. The hydrogen generation measurement showed that the average hydrogen generation rate at was for unsupported Co–B catalyst, while it was 1268.1, 1482.1 and for the carbon-supported catalysts with the Co–B loading of 30.0, 15.6 and 7.44 wt%, respectively. The activation energy of the 30.0 wt% Co–B loading catalyst for the hydrogen generation reaction was measured to be . Compared with the unsupported Co–B catalyst, the as-prepared carbon-supported catalysts presented higher activity for hydrolysis of NaBH₄ aqueous solution, indicating their potential application in mobile hydrogen production for fuel cells.     

Investigation on microstructures and electrochemical performances of hydrogen storage alloys

In order to improve the cycle stability of La–Mg–Ni system (A₂B₇-type) alloy electrode, a small amount of Co was added in the La_0.75Mg_0.25Ni_3.5 alloy. The effects of Co content on the microstructures and electrochemical performances of the alloys were investigated in detail. The results by XRD and SEM show that the alloys have a multiphase structure which is composed of the LaNi₅, (La,Mg)₂Ni₇ two major phases and a small amount of the LaNi₂ phase. The cell volumes of the LaNi₅ and phases enlarge with the increasing Co content in the alloys. With the increasing Co content, some electrochemical properties and kinetic parameters of the alloy, involving the discharge capacity, high-rate discharge ability (HRD), the polarization resistance (R_p), the loss angle (ψ) and the limiting current density (I_L), first increase and then decrease. The addition of Co slightly improves the cycle stabilities of the alloy electrodes. The mechanism of the efficiency loss of the experimental alloy was investigated by means of SEM and X-ray photoelectron spectroscopy (XPS). The results indicate that the fundamental reasons for the capacity decay of the La_0.75Mg_0.25Ni_3.5Co_x (x=0,0.2,0.4,0.6) alloy electrodes are the pulverization of the alloy particle and corrosion/oxidation of La and Mg in alkaline electrolyte.     

A theoretical study of the electronic structure and bonding of the monoclinic phase of

The electronic properties of the Mg₂NiH₄ monoclinic phase are calculated using a density functional approach calculation. The crystalline parameters and interatomic distances calculated are close to the experimental values within a 3% error. We also evaluate the density of states (DOS) and character of the chemical bonding for the hydrogen's located in their equilibrium positions. While the Ni–Mg interaction is dominant in the pure alloy, in the hydride the hydrogen atoms present a bonding much more developed with Ni than with Mg. The principal bonding interaction is Ni sp–H s. Moreover, a small bonding between Ni d_eg and H 1s is observed. Up the Fermi level, the Ni–H interaction is slightly antibonding. The Mg–Ni bonding interactions are weaker in the hydride phase when compared with the pure Mg₂Ni alloy. The present study is potentially useful because the alloys Mg–Ni are good materials for hydrogen storage.     

Preparation of thin films by sulfurizing sol–gel deposited precursors

Cu₂ZnSnS₄ (CZTS) thin films were prepared by sulfurizing precursors deposited by the sol–gel method. Copper (II) acetate monohydrate, zinc (II) acetate dihydrate and tin (II) chloride dihydrate were used as the starting materials of the sol–gel method, and 2-methoxyethanol and monoethanolamine were used as the solvent and the stabilizer, respectively. The solution was spin coated on soda lime glass substrates and dried at . The coated glasses were sulfurized by annealing at in a hydrogen sulfide-containing atmosphere. The annealed thin films showed X-ray diffraction peaks attributed to the single phase CZTS. The chemical composition of the films was almost stoichiometric and the band gap energy was at room temperature.     

Dye-sensitized solar cell using natural dyes extracted from rosella and blue pea flowers

Dye-sensitized solar cells (DSSCs) were fabricated using natural dyes extracted from rosella, blue pea and a mixture of the extracts. The light absorption spectrum of the mixed extract contained peaks corresponding to the contributions from both rosella and blue pea extracts. However, the mixed extract adsorbed on TiO₂ does not show synergistic light absorption and photosensitization compared to the individual extracts. Instead, the cell sensitized by the rosella extract alone showed the best sensitization, which was in agreement with the broadest spectrum of the extract adsorbed on TiO₂ film. In case that the dyes were extracted at , using water as extracting solvent, the energy conversion efficiency (η) of the cells consisting of rosella extract alone, blue pea extract alone and mixed extract was 0.37%, 0.05% and 0.15%, respectively. The sensitization performance related to interaction between the dye and TiO₂ surface is discussed. The explanations are supported by the light absorption of the extract solution compared to extracts adsorbed on TiO₂ and also dye structures. The effects of changing extracting temperature, extracting solvent and pH of the extract solution are also reported. The efficiency of rosella extract sensitized DSSC was improved from 0.37% to 0.70% when the aqueous dye was extracted at instead of and pH of the dye was adjusted from 3.2 to 1.0. Moreover, DSSC stability was also improved by the changes in conditions. However, the efficiency of a DSSC using ethanol as extracting solvent was found to be diminished after being exposed to the simulated sunlight for a short period.     

Activation characteristics and microstructure of composite hydrogen storage alloys prepared by two-step re-melting

In the present work, novel composites (x=0,5,10,30) for hydrogen storage were prepared by two-step re-melting and their activation characteristic and microstructure were investigated. The influence of Mg₂Ni content on the activation characteristics was analyzed by electrochemical method. With the increasing content of Mg₂Ni, activation characteristics and maximum discharge capacities of composites increase first and then decrease. The composite with 5% Mg₂Ni has the least cycle number for activation and the highest discharge capacity. It is activated after only 6 cycles (C_n=6) at room temperature and its maximum discharge capacity (C_max) reaches 274.4 mAh/g. However, the composite contained 30 wt% Mg₂Ni is difficult to be activated at room temperature. It is also found that it is easier to be activated for the composites at and than that at and , but their discharge capacity decay slightly at the condition of and . The XRD and SEM analysis show that, with the increasing Mg₂Ni content, the microstructure of the composites varies gradually from lamellar (x=5), acicular (x=10) to massive (x=30), and the activity of the composite declines as a result of the grain size of phase Mg₂Ni grows up.     

International passenger transport and climate change: A sector analysis in car demand and associated emissions from 2000 to 2050

The paper provides global regionalized projections of passenger car demand, use and associated CO₂ emissions from 11 world regions. The study is based on empirical data that have been originally collated from international sources for the purpose of modeling region-specific car stock demand. Derived demands serve as indicator of car related fuel consumption and associated CO₂ emissions, which are calculated on the basis of behavioral and technological scenarios. The obtained CO₂ emission paths are sectoral baseline scenarios that identify region-specific potentials of growth in car induced CO₂ emissions assuming that current trends continue to prevail. The study adopts a multi-model approach to car demand by applying two methodologies rooted in the economics of consumption: utility maximization and single equation models. The utility maximization method for modeling car demand is driven by the preferences of the representative consumers of each world region, subject to exogenous price and income trajectories. The latter is adopted from an optimal growth model. This is a novel approach to projecting global regionalized sectoral car demands. The study is complemented by the application of single equation income–consumption models based on logistical Gompertz functions and non-linear regression techniques to compare model results.     

Ex situ investigation of the proton exchange membrane chemical decomposition

The durability of Nafion^® polymer electrolyte membranes (PEMs) with potential application in PEM fuel cells has been investigated using accelerated durability tests to understand their degradation mechanism. After the attack by Fenton radicals, the Nafion^®111 membranes and the solution produced were collected for analysis. The existence of F ions in the solution indicated the chemical decomposition of the Nafion^® membranes during radical attacks. The F^- emission rate (FER) was about , corresponding to 0.024 wt% of F released from the membrane per hour. The NMR and FTIR spectrums demonstrated the polymer fragments mostly existed as whole side chains of the Nafion^® membrane. This result revealed that the degradation was originated from the decomposition of polymer main chain. Furthermore, the reflectance-FTIR revealed that the degradation of the PEMs was from the decomposition of the repeating units in the polymer main chains. With the increased loss of repeating units, small bubbles with the diameter of several microns started to form in Nafion^® membrane. These bubbles made the membrane vulnerable to hazards of gas crossover, which further led a catastrophic failure of the proton exchange membrane.     

A wide range modeling study of formation and nitrogen chemistry in hydrogen combustion

The chemistry of nitrogen species and the formation of NO_x in hydrogen combustion are analyzed here on the basis of a large set of experimental measurements.The detailed kinetic scheme of H₂/O₂ combustion was updated and upgraded using new kinetic and thermodynamic measurements, and was validated over a wide range of temperatures, pressures and equivalence ratios. The mechanism's performance at high pressures was greatly improved in particular by adopting higher rate parameters for the H+OH+M=H₂O reaction.The NO_x sub-mechanism was further validated and updated. The kinetic parameters of the NO₂+H₂=HONO+H and N₂H₂+NO=N₂O+NH₂ reactions were updated in order to improve model predictions in specific conditions.Sensitivity analyses were carried out to determine which reactions dominate the H₂/O₂ and H₂/NO_x systems at particular operating conditions.Good overall agreement was observed between the model and the wide range of experiments simulated.     

Simulation of methane conversion to syngas in a membrane reactor: Part I A model including product oxidation

A one-dimensional dense membrane reactor (DMR) model has been developed to simulate the partial oxidation of methane to syngas. A combustion–reforming mechanism was adopted and the oxidation of reforming products, i.e. H₂ and CO, was considered. The performance of the DMR and a conventional fixed-bed reactor was compared and discussed. The results show that the incorporation of the product oxidation steps has a significant effect on the simulation results of a DMR and provides a reasonable explanation of the experimental data. The model is therefore more reasonable than those ignoring the product oxidation reactions.     

Carrier collection in Cu(In,Ga)Se2 solar cells with graded band gaps and transparent ZnO:Al back contacts

Cu(In,Ga)Se₂ Solar cells with graded band gap and efficiencies up to 13% have been fabricated on transparent ZnO:Al back contacts. The back contact structure includes a transparent 10 nm thin Mo interlayer with NaF precursor between the ZnO:Al and the Cu(In,Ga)Se₂ absorber that transforms the blocking ZnO:Al/Cu(In,Ga)Se₂ interface into an Ohmic back contact. To investigate the electronic quality of the back contact, the cells are analyzed by internal quantum efficiency measurements under illumination from front and back side. A new semianalytical model for the quantum efficiency of graded band gap absorbers yields quantitative information about the back contact recombination velocity as well as optical and electronic material parameters of the absorber layer. Band gap grading significantly increases carrier collection. However, in the immediate vicinity of the back contact carrier collection is limited by a high ratio of back contact recombination velocity and diffusion constant .     

Microcrystalline silicon deposited at high rate on large areas from pure silane with efficient gas utilization

Microcrystalline silicon thin film deposited by RF-PECVD and integrated in a tandem structure is a promising material for low cost photovoltaic solar cells compared to solar cells based on crystalline silicon. However, in order to allow a cost-effective mass production of solar cells based on this material, deposition processes should fulfill several conditions such as high deposition rate, good uniformity over large area and efficient gas utilization. In this work, it is shown that the atomic hydrogen density can be high enough to form microcrystalline thin films even from a pure silane RF discharge and that the pure silane regime is more efficient in terms of gas utilization. In situ Fourier transform infrared absorption and ex situ Raman spectroscopy measurements have been used to determine the fraction of dissociated silane in the discharge and the crystallinity of the deposited layers. Results have shown that microcrystalline silicon can be deposited uniformly on a large area substrate with a deposition rate of more than with a low powder formation and an input power density of from a pure silane discharge.     

Mass production of alloy bulk by isothermal evaporation casting process

An innovative method, isothermal evaporation casting process (IECP), is developed to produce Mg₂Ni alloy for mass production in this work. In the past, high vapor pressure of Mg was considered as a disadvantage for producing pure Mg₂Ni alloy. However, this characteristic was used to develop a refinement procedure to separate primary Mg₂Ni alloy from Mg/Mg₂Ni eutectic matrix. Characteristics of as-cast specimens measured by X-ray diffraction (XRD), inductively coupled plasma-atomic emission spectroscopy (ICP-AES) and electron probe X-ray microanalyzer (EPMA) reveal that mass production of single phase Mg₂Ni alloy was successfully fabricated by IECP. For every 4.0 kg of raw materials, alloy bulk was extracted at a yield of about 65%. The hydrogen storage capacity of the well-activated Mg₂Ni alloy reaches 3.58 wt% at 300 °C under 40 atm H₂ atmosphere which is close to the theoretical capacity of 3.6 wt%.     

Fundamental time–domain wind turbine models for wind power studies

One critical task in any wind power interconnection study involves the modelling of wind turbines. This paper provides the most basic yet comprehensive time–domain wind turbine model upon which more sophisticated models along with their power and speed control mechanisms, can be developed. For this reason, this paper concentrates on the modelling of a fixed-speed wind turbine. The model includes turbine's aerodynamic, mechanical, and electrical components. Data for the rotor, drive-train, and electrical generator are given to allow replication of the model in its entirety. Each of the component-blocks of the wind turbine is modelled separately so that one can easily expand the model to simulate variable-speed wind turbines or customise the model to suit their needs. Then, an aggregate wind turbine model, or wind farm, is developed. This is followed by four case studies to demonstrate how the models can be used to study wind turbine operation and power grid integration issues. Results obtained from the case studies show that the models perform as expected.     

Microstructure and hydrogen storage properties of the laser sintered alloy

The Mg₂Ni hydrogen storage samples were prepared by the laser sintering method. Before laser sintering, the Mg and Ni powders were pre-mixed by pestle milling (sample PM) or ball milling (sample BM). The microstructures and hydrogen storage properties of the laser sintered Mg₂Ni samples were investigated. The sintered samples contained Mg₂Ni and small amount of MgNi₂, Mg, Ni and MgO. Compared with the sample PM, the amounts of Mg₂Ni and MgNi₂ reduced and the amounts of Mg and Ni increased in the sample BM. The laser sintered Mg₂Ni samples can be activated easily at 573 K. The maximum hydrogen storage capacities of the PM and BM samples were 3.23 and 3.44 wt%, respectively.     

Simultaneous hydrogen production and decomposition of dissolved in alkaline water over composite photocatalysts under visible light irradiation

A process of simultaneous hydrogen production and H₂S removal has been investigated over a highly active composite photocatalyst made of bulk CdS decorated with nanoparticles of TiO₂, i.e. CdS(bulk)/TiO₂. The photocatalytic activity was evaluated for hydrogen production from aqueous electrolyte solution containing H₂S dissolved in water or alkaline solution under visible light irradiation. The rate of hydrogen production from the H₂S-containing alkaline solution was similar to the rate obtained from photocatalytic hydrogen production from water containing sacrificial reagents (Na₂S+Na₂SO₃) in the similar concentration. The isotope experiment was carried out with D₂O instead of H₂O to investigate the source of hydrogen from photocatalytic decomposition of H₂S dissolved in H₂O or alkali solution under visible light. Hydrogen originated from both H₂S and H₂O when the reaction solution contained H₂S absorbed in alkaline water.     

A numerical study of natural convection around a square,horizontal, heated cylinder placed in an enclosure

In this paper, natural convection around a tilted heated square cylinder kept in an enclosure has been studied in the range of 10³ ⩽ Ra ⩽ 10⁶. Streamfunction-vorticity formulation of the Navier–Stokes equation is solved numerically using finite-difference method in non-orthogonal body-fitted coordinate system. Detailed flow and heat transfer features for two different thermal boundary conditions are reported. Effects of the enclosure geometry has been assessed using three different aspect ratio placing the square cylinder at different heights from the bottom. The concept of heatfunction has been employed to trace the path of heat transport. It is found that the uniform wall temperature heating is quantitatively different from the uniform wall heat flux heating. Flow pattern and thermal stratification are modified, if aspect ratio is varied. Overall heat transfer also changes for different aspect ratio.     

On various modeling approaches to radiative heat transfer in pool fires

Six computational methods for solution of the radiative transfer equation in an absorbing-emitting, nonscattering gray medium were compared for a 2-m JP-8 pool fire. The emission temperature and absorption coefficient fields were taken from a synthetic fire due to the lack of a complete set of experimental data for computing radiation for large and fully turbulent fires. These quantities were generated by a code that has been shown to agree well with the limited quantity of relevant data in the literature. Reference solutions to the governing equation were determined using the Monte Carlo method and a ray-tracing scheme with high angular resolution. Solutions using the discrete transfer method (DTM), the discrete ordinates method (DOM) with both S₄ and LC₁₁ quadratures, and a moment model using the M₁ closure were compared to the reference solutions in both isotropic and anisotropic regions of the computational domain. Inside the fire, where radiation is isotropic, all methods gave comparable results with good accuracy. Predictions of DTM agreed well with the reference solutions, which is expected for a technique based on ray tracing. DOM LC₁₁ was shown to be more accurate than the commonly used S₄ quadrature scheme, especially in anisotropic regions of the fire domain. On the other hand, DOM S₄ gives an accurate source term and, in isotropic regions, correct fluxes. The M₁ results agreed well with other solution techniques and were comparable to DOM S₄. This represents the first study where the M₁ method was applied to a combustion problem occurring in a complex three-dimensional geometry. Future applications of M₁ to fires and similar problems are recommended, considering its similar accuracy and the fact that it has significantly lower computational cost than DOM S₄.     

On the spectral bands measurements for combustion monitoring

In this work, spatial–spectral experimental issues affecting the detection of radical emissions in a natural gas flame are discussed and studied by a radiometric analysis of the flame spectral emission. As results of this analysis, Local and Global Spectral Radiation Measurements (LSRM and GSRM respectively) techniques are proposed, and guidelines for selecting the radical emission bands and spatial location of photodetectors are given. Two types of experiments have been performed in order to demonstrate the reliability of the GSRM technique for combustion characterization. In the first experiment, the LSRM and the GSRM have been implemented by using a home made sensor array, based on silicon photodiodes, for sensing the excited CH^∗ and radicals in a natural gas flame. It has been experimentally demonstrated that by using the GSRM, the signal’s dispersion can be reduced to about 86% for the CH^∗ and 76% for the with respect to the obtained values with LSRM methodology. In the second experiment, the GSRM technique has been applied for sensing the CH^∗ and radicals, where it has been found that the signals emissions ratio /CH^∗ provides a good indicator of the thermal combustion efficiency and the CO pollutants emissions, with small dispersion. Thus, the GSRM technique has corroborated the usefulness of that ratio for combustion monitoring.     

Natural convection in rectangular enclosures heated from below and cooled along one side

Steady natural convection in a square, water-filled enclosure heated from below and cooled on one vertical side is studied analytically and numerically. Expansions for small Rayleigh number are developed to order Ra². It is found that the first contribution to the convective heat transfer occurs at order Ra². Asymptotic expressions are found for the temperature and heat transfer near the flux singularity on the enclosure floor. Finite difference numerical simulations indicate that the present condition (heating from below) is quite distinct from the case of cooling from below and heating on one vertical wall. Convective heat transfer is shown to be most significant when slightly less than half of the lower surface is heated.