Photoreduction of N2 to NH3 and H2O to H2 on metal doped TiO2 catalysts (M = Ce, V)

The photosynthesis of NH₃ from N₂ and the photogeneration of H₂ from H₂O under non-sacrificial conditions on M/TiO₂ (M = Ce, V) are reported. The yields are superior to those earlier reported for similar metal doped TiO₂ catalysts. The flat band potentials of these catalysts have been determined and correlated to their catalytic activity.     

Comparative frequency-resolved photoconductivity studies of amorphous semiconductors

Comparative frequency-resolved photoconductivity measurements in amorphous (a-) semiconductors, such as a-Si:H p–i–n junction, a-SiGe:H and a-chalcogenides (a-Se, a-As₂Se₃, a-As₂Te₃, a-SeTe, a-As₂S₃, etc.) are reported. In particular, photoconductivity lifetimes as a function of light intensity and temperature were determined by using the quadrature frequency-resolved spectroscopy method. The activation energies from the temperature-dependent lifetime and photocurrent were determined and compared in different materials. The exponent ν in the power-law relationship (I_ph∝G^ν) between generating flux and photocurrent was also obtained at different excitation wavelengths. The results were compared with the predictions of multiple-trapping (MT) and distant-pair (DP) models developed for photoconductivity of a-semiconductors at high and low temperatures, respectively.     

Measurement of CO2 solubility in pure water and the pressure effect on it in the presence of clathrate hydrate

The solubility of CO₂ in pure water was investigated under high-pressure conditions, from 7 to 12 MPa. Temperature varied between 2.5-20 °C. CO₂ clathrate hydrate formed at temperatures below approximately 10 °C. Saturated concentrations of CO₂ were determined from expanding dissolved gas. The solubility in the presence of the hydrate decreased with decreasing temperature and with decreasing pressure, although some researchers reported it decreased with higher-pressure conditions at about 7 °C. Many other researchers reported that the pressure conditions did not affect the solubility in the presence of the hydrate. Although this is mostly correct, we did confirm a small difference in solubility due to pressure conditions.     

Ni-Ce/SiO2 nanocomposite: Characterization and catalytic activity in the cracking of tar in biomass gasifiers

The synthesis of Ni/SiO₂ and Ni-Ce/SiO₂ nanocomposites by deposition–precipitation method (DPM) has been reported. The nanocomposites were characterized by XRD, HR-SEM, HR-TEM, and BET. The XRD results confirmed the formation of Ni/SiO₂ and Ni-Ce/SiO₂ nanocomposites. The sphere-like morphology of Ni/SiO₂ and Ni-Ce/SiO₂ were confirmed by HR-SEM and HR-TEM. Surface area of the sample was determined by BET analysis. Furthermore, the prepared nanocomposites have been used as a catalyst in the cracking of tar. The tar cracking efficiencies of Ni/SiO₂ and Ni-Ce/SiO₂ nanocomposites were 93.0% and 98.5%, respectively, at a catalytic bed temperature of 800°C.     

Structural and hydrogen sorption properties of SmNi5−xGax system – an experimental and theoretical study

A series of ternary alloys of general formula SmNi_5−xGa_x (x = 0.25, 0.5, 1.5, 2, 2.5) was prepared by melting mixtures of Sm, Ni and Ga in arc furnace under argon. From X-ray powder diffraction lattice parameters are determined and it is found that hexagonal structure of P6/mmm space group is retained for all considered values of x. Hydrogen absorption ability and thermodynamic quantities of the systems are determined by pressure-composition desorption isotherms. The obtained properties are compared with those of previously reported SmNi₅ and SmNi₄Ga. DFT calculations were performed for selected members of the system and the results are discussed with regard to experiment.     

Microwave assisted synthesis of ruthenium electrocatalysts for oxygen reduction reaction in the presence and absence of aqueous methanol

In this work we present the synthesis of ruthenium based electrocatalysts for oxygen reduction reaction in 0.5 mol L⁻¹ H₂SO₄, using microwave irradiation at different power, time and temperature conditions. Ru₃(CO)₁₂ and 1,2-dichlorobenzene were used as precursor and solvent respectively. The materials obtained were structurally characterized by FT-IR spectroscopy and X-ray diffraction; their chemical composition was determined by energy-dispersive spectroscopy analysis. The rotating disk electrode technique was used for the electrochemical characterization of the catalysts; the oxygen reduction reaction was performed in the presence and absence of aqueous methanol solutions. The electrocatalytic activity towards the oxygen reduction reaction is similar to that of ruthenium catalysts synthesized using a conventional process reported in the literature.     

Novel experimental methods for assessment of hydrogen storage capacity and modelling of sorption in Cu-BTC

Novel experimental procedures for hydrogen adsorption studies are presented. The methods provide an important advantage: pure material sorption behaviour can be directly determined without the use of equations of state (EOS) at low temperatures. The storage properties of Cu-BTC [Cu₃(BTC)₂, BTC – 1,3,5-benzenetricarboxylate] were investigated under different thermodynamic conditions. The maximum hydrogen uptake of 4.6 wt% was observed at 25 K. We compared the results obtained in this work with previously reported experimental data to prove the validity of the novel methods for the hydrogen sorption measurements. The experimental data of the present work show a good agreement with the results reported in the literature. Additionally, the modelling of the hydrogen sorption processes in Cu-BTC was carried out. The simulations were performed in the form of isotherms and isobars. Fairly good agreement with experimental data has been achieved. Uncertainties in MOF-H₂ interactions are most likely the major reasons for the remaining difference between simulations and experiments.     

Biotechnological approach to generate green biohydrogen through the utilization of succinate-rich fermentation wastewater

Photofermentation seems to be an attractive mode of generating biohydrogen from fermentation effluent. Use of succinate fermentation effluent, however, has not been reported. Rhodobacter sphaeroides KKU-PS1 and Rhodopseudomonas palustris were acclimatised in succinate. It was determined that the KKU-PS1 was superior with respect to hydrogen productivity and was selected for further experiments. Photofermentation in succinate by the KKU-PS1 validated, generating 1217 mL H₂/L of cumulative hydrogen at a maximum rate of 6.7 mL H₂/L/h. Photofermentation from each single carbon sources that are components of effluent was performed and it was determined that acetate and succinate promoted the fastest growth of KKU-PS1 and hydrogen evolution, respectively. Photofermentation by the strain using mixed substrates mimicking diluted bio-succinate effluent produced yielded 1005 mL H₂/L cumulative hydrogen at a maximum rate of 4.1 mL H₂/L/h. The study highlighted potential of utilizing bio-succinate fermentation effluent for biohydrogen production, with further optimization required.     

A composite carbon anode for use in a polymer electrolyte battery

A composite carbon anode has been developed for a room temperature polymer electrolyte cell using poly(ethylene oxide) (PEO). By means of half-cells the charge/discharge process has been studied and the specific capacity of the Li_xC₆ electrode as a function of cycle number determined. This has been supported by impedance analysis which has been carried out at various electrode compositions. Data on the effect of carbon content on performance and the influence of elevated temperature (40°C) are reported. Good cycleability of a polymer electrolyte cell comprising a carbon anode, PEO-based electrolyte and a high voltage intercalating cathode LiMn₂O₄ has been demonstrated.     

Water purification using solar energy: effect of sulphur on photocatalytic properties of TiO2

Abstract

The present work considers the effect of sulphur on several properties of titanium dioxide (TiO₂) including electronic structure, defect disorder and photocatalytic properties. While the reports on the mechanism of sulphur incorporation into the TiO₂ lattice are conflicting, there is a consensus that sulphur leads to reduction of band gap and enhanced photocatalytic performance. The latter effect suggests that light absorption, which is determined by an electronic structure, plays the key role in the conversion of the light energy into the chemical energy that is required for photocatalytic decomposition of organic contaminants in water. Analysis of the reported data suggests that different processing procedures result in different doping mechanisms. It is argued that most of the experimental data reported so far are not well defined and, therefore, are not compatible. Consequently, the progress in the science of photocatalysis requires collection of empirical data that are well defined.     

Current status and progress of direct borohydride fuel cell technology development

In this review article, recent advances in the development of the direct borohydride fuel cell (DBFC) technology are reviewed. Based on the reported results, it is concluded that the BH₄⁻ electro-oxidation is determined by the catalyst used and BH₄⁻ concentration at the catalytic sites. Hydrogen evolution during the DBFC operation can be suppressed by: (1) using a composite catalyst or a hydrogen storage alloy as the anode catalyst via a quasi 8-electron reaction; (2) using metals with high hydrogen over-potential, such as Au and Ag as the anode catalyst via an intrinsic 8-electron reaction; and/or (3) modifying and optimizing fuel composition.     

Electrochemical characterization of LixNiyCo1−yO2 electrodes in a 1 M LiPF6 solution of the ethylene carbonate–diethyl carbonate

The electrochemical characteristics of Li_xNi_yCo_1−yO₂ (0.5<y<0.9) prepared by a co-precipitation method were reported. Slow scan cyclic voltammetry (SSCV) and electrochemical impedance spectroscopy (EIS) were used to investigate the kinetic behavior of the composite electrodes. Kinetic data such as the Tafel slope and the charge-transfer resistance were determined based on the experimental results. An equivalent circuit model was proposed to simulate the impedance spectra and gave a good data fit. The present study also demonstrated that the kinetic data were composition-sensitive to varying lithium content and nickel content in the mixed oxide electrodes.     

A study of tungsten nanopowder formation by self-propagating high-temperature synthesis

Molten salt-assisted self-propagating high-temperature synthesis of nanocrystalline W powder was studied experimentally. The technique involves the reduction of WO₃ in the presence of sodium chloride using three different reducing agents: magnesium (Mg), sodium azide (NaN₃), and sodium borohydride (NaBH₄). The effects of the mole fraction of sodium chloride on temperature distributions, combustion parameters, phase compositions, and morphology of the final products were determined. The sodium chloride-assisted method reported here has been found to be effective for lowering combustion temperature and producing uniform and spherical W nanopowders of average particle size around 20-200, 100-200, and 20-50 nm. The effect of combustion temperature on tungsten particle size is discussed, and a sketch describing the chemistry of combustion is proposed.     

Preparation and characterization of thin films of electrodeposited CdTe semiconductors

Thin films of CdTe semiconductors were prepared by electrodeposition technique in aqueous solutions. The deposition mechanism was investigated by cyclic voltammetry. The potential regions for the formation of the n-CdTe and p-CdTe films were determined. The structure, composition and morphology characteristics of as-deposited thin films of CdTe grown on SnO₂/glass and CdS/SnO₂/glass were investigated by XRD, EDAX and SEM techniques. The optical properties were measured to determine the absorption coefficient and band gap values. The as-deposited CdTe films grown on SnO₂/glass contained free Te while those grown on CdS/SnO₂/Glass did not contain this phase. The CdTe has the cubic structure with strong (111) orientation. The EDAX analysis showed a nearly stiochiometric Cd:Te ratio. The band gap has a value of 1.48 eV, which is in a good accordance with those reported in the literature. The effect of annealing at 350 and 400°C after CdCl₂ treatment on the structure and morphology was also examined.     

Determination of the boundary of carbon formation for dry reforming of methane in a solid oxide fuel cell

The boundary of carbon formation for the dry reforming of methane in direct internal reforming solid oxide fuel cells (DIR-SOFCs) with different types of electrolyte (i.e., an oxygen ion-conducting electrolyte (SOFC-O²⁻) and a proton-conducting electrolyte (SOFC-H⁺)) was determined by employing detailed thermodynamic analysis. It was found that the required CO₂/CH₄ ratio decreased with increasing temperature. The type of electrolyte influenced the boundary of carbon formation because it determined the location of water formed by the electrochemical reaction. The extent of the electrochemical reaction also played an important role in the boundary of carbon formation. For SOFC-O²⁻, the required CO₂/CH₄ ratio decreased with the increasing extent of the electrochemical reaction due to the presence of electrochemical water in the anode chamber. Although for SOFC-H⁺ the required CO₂/CH₄ ratio increased with the increasing extent of the electrochemical reaction at high operating temperature (T > 1000 K) following the trend previously reported for the case of steam reforming of methane with addition of water as a carbon suppresser, an unusual opposite trend was observed at lower operating temperature. The study also considered the use of water or air as an alternative carbon suppresser for the system. The required H₂O/CH₄ ratio and air/CH₄ ratio were determined for various inlet CO₂/CH₄ ratios. Even air is a less attractive choice compared to water due to the higher required air/CH₄ ratio than the H₂O/CH₄ ratio; however, the integration of exothermic oxidation and the endothermic reforming reactions may make the use of air attractive. Water was found to be more effective than carbon dioxide in suppressing the carbon formation at low temperatures but their effect was comparable at high temperatures. Although the results from the study were based on calculations of the SOFCs with different electrolytes, they are also useful for selecting suitable feed compositions for other reactors; including conventional reformers and membrane reactors with hydrogen removal.     

The oxygen-releasing step in the water splitting cycle by MnFe2O4–Na2CO3 system

Investigation of the feasibility of the thermochemical two-step water splitting cycle based on MnFe₂O₄/Na₂CO₃ system is reported. Influence of temperature and carbon dioxide pressure on the oxygen-releasing step was investigated. XRD analysis was applied to obtain phase identification of reacted powders at investigated experimental conditions. Different sodium sub-stoichiometric Na_1−δ(Mn_1/3Fe_2/3)O_2−δ/2 compounds were observed and their structure determined by using Rietveld analysis. Selected experimental conditions permitted to define a T/pCO2$T/p_{{\text{CO}}_{\text{2}}}$ phase diagram, showing different solid phases coexistence regions. Experimental conditions that permit complete regeneration of the initial MnFe₂O₄/Na₂CO₃ mixture were identified (field I in the reported diagram), demonstrating the possibility of full chemical cyclical operation of the system.     

Dopant-induced surface activation of ceria nanorods for electro-oxidation of hydrogen and propane in solid oxide fuel cells

Ceria is an excellent oxide catalyst to break H₂ in the absence of noble metals and has shown great promise for potential applications in diverse technological fields. The catalytic activity of ceria is critically linked to surface composition and structure. Herein, selective doping with moderate lanthanide ions is reported to regulate surface oxygen vacancies and bonded adsorbates of ceria nanorods so as to finely tune their activities toward electro-oxidation of H₂ and C₃H₈ in reduced-temperature solid oxide fuel cells. Lanthanide doped ceria nanorods are hydrothermally synthesized, and electrochemically evaluated as the anode catalysts for reduced-temperature SOFCs. Measurements of anode polarization resistances and fuel cell power densities show a catalytic activity in the order of Ce_0.8Pr_0.2O_2-δ < Ce_0.8Gd_0.2O_2-δ < Ce_0.8Sm_0.2O_2-δ. Probing the surface structure with hydrogen temperature-programmed reduction, UV-Raman and XPS reveals that such catalytic activities are essentially determined by surface reducibility, availability of surface oxygen vacancies and strongly bonded hydroxyls.     

In-situ synthesis of Ag-Pi oxygen-evolving catalyst in phosphate environment for water splitting

An efficient Ag-P_i oxygen-evolving catalyst was fabricated in situ in a phosphate electrolyte solution (pH 12.4). The catalyst approaches an amorphous structure, unlike the reported Ag-based oxygen-evolving catalysts. The catalytic activity for water oxidation of the Ag-P_i catalyst is 11.1 μmol h^?1 cm^?2 and it has a modest oxygen-evolution overpotential of 457.0 mV at 1 mA cm^?2 in 0.1 M K₃PO₄ electrolyte. The effects of different electrolytes on the formation of the Ag-P_i catalyst were investigated. The active component of the Ag-P_i oxygen-evolving catalyst as a water-splitting catalyst is the AgO phase as determined by X-ray diffractometry and X-ray photoelectron spectroscopy analysis. A Ag-P_i mechanism that includes the Ag(I) and Ag(III) cycles is proposed to explain the electrocatalytic oxygen evolution.     

On the ionic character of H2 separation through mixed conducting Nd5.5W0.5Mo0.5O11.25−δ membrane

Nd_5.5W_0.5Mo_0.5O_11.25?δ exhibits high total conductivity in reducing atmospheres and a significant H₂ permeation at high temperature. Nevertheless, the partial contribution from electrons, protons and oxide-ions in this material is still not reported. In this work, an exhaustive electrochemical study has been performed for Nd_5.5W_0.5Mo_0.5O_11.25?δ. The total conductivity has been studied systematically in different environments, analyzing the influence of the temperature, pO₂ and pH₂O. Transport numbers have been determined from the EMF measurement in concentration cells. H₂ permeation measurements for Nd_5.5W_0.5Mo_0.5O_11.25?δ have been performed from 725 to 625 °C and H/D isotopic studies were carried out at 700 °C. By coupling all these techniques, a complete overview of the transport mechanisms in the material has been achieved.     

Matching analysis of photovoltaic powered dc series motors and centrifugal pumps by varing motor constants

An analytical method for the direct coupling between a photovoltaic (PV) generator and a monoblock DC series motor driven centrifugal pump has been developed as a function of the no-flow motor-pump speed w₀ and its working speed w. w₀ is a function of the motor terminal voltage, and w is determined by the value of w₀ and the working water head of the pump. The different parameters of a monoblock DC series motor and a centrifugal pump have been derived as variables of w₀ and w. The optimum matching conditions at the maximum hydraulic efficiency are discussed. The mathematical approach to this study has been verified by experimental results from two different pump systems. The constants of a given motor-pump system are constrained by the requirements and design factors. Without alteration of these constants, better matching can be achieved only by changing the motor constant M₀. Some reported results also compare well with those of this model.