Hydrogenation properties of Mg-based composites prepared by reactive mechanical alloying

A nanocrystalline composite of Mg–LaNi₃–Cu has been prepared by reactive mechanical alloying of Mg, Cu and LaNi₃ powders after 60 h ball-milling under a hydrogen atmosphere. This composite desorbed 1.06 mass% of hydrogen at 533 K under a hydrogen pressure of 0.1 MPa. Addition of Cu promotes the hydrogen desorption.     

Preparation and characterization of NbF5-added Mg hydrogen storage alloy

A sample with a composition of 95 wt% Mg-5 wt% NbF₅ (named Mg-5NbF₅) was prepared by reactive mechanical grinding using Mg instead of MgH₂ as a starting material. Its hydriding and dehydriding rates were then measured under nearly constant hydrogen pressures. The activation of Mg-5NbF₅ was not required, and Mg-5NbF₅ had an effective hydrogen storage capacity, which was defined as the quantity of hydrogen absorbed for 60 min, of 5.50 wt%. At the first cycle (n = 1) at 593 K, the sample absorbed 4.37 wt% H for 5 min and 5.50 wt% H for 30 min under 12 bar H₂, and desorbed 1.03 wt% H for 5 min, 4.66 wt% H for 30 min, and 5.43 wt% H for 60 min under 1.0 bar H₂. Reactive mechanical grinding of Mg with NbF₅, which formed MgH₂, MgF₂, NbH₂, and NbF₃ by the reaction of 11 Mg + 7NbF₅ + 3H₂ → MgH₂ + 10MgF₂ + 2NbH₂ + 5NbF₃, is considered to create defects, to produce reactive clean surfaces, and to reduce the particle size of Mg. The XRD pattern of Mg-5NbF₅ dehydrided at n = 3 revealed Mg, small amounts of β-MgH₂ and MgO, and very small amounts of MgF₂ and NbH₂. An increase in the dehydriding rate of Mg-5NbF₅ was attempted by adding Ni to Mg-5NbF₅. Mg-5NbF₅ had higher initial hydriding and dehydriding (after the incubation period) rates and a larger effective hydrogen storage capacity than Mg-10NbF₅, Mg-10MnO, and Mg-10Fe₂O₃, which were reported to have quite high hydriding rate and/or dehydriding rate.     

Improvement of hydrogen storage characteristics of Mg by planetary ball milling under H2 with metallic element(s) and/or Fe2O3

Among samples of Mg-Ni, Mg-Ni-5Fe₂O₃, and Mg-Ni-5Fe, Mg-Ni-5Fe had the highest hydriding and dehydriding rates. For the as-milled Mg-Ni-5Fe alloy and the hydrided Mg-Ni-5Fe alloy after activation, the weight percentages of the constituent phases were calculated using the FullProf program. The creation of defects and the diminution of Mg particle size through reactive mechanical grinding and hydriding-dehydriding cycling, and the formation of the Mg₂Ni phase are considered to increase the hydriding and dehydriding rates. Mg-14Ni-2Fe-2Ti-2Mo had higher hydriding and dehydriding rates than did any of the other samples (Mg-Ni, Mg-Ni-5Fe₂O₃, Mg-Ni-5Fe, and Mg-14Ni-6Fe₂O₃) prepared in this work.     

Effects of Ni,Fe2O3, and CNT addition by reactive mechanical grinding on the reaction rates with H2 of Mg-based alloys

Ni, Fe₂O₃, and CNT were added to Mg. The content of the additives was about 20 wt % with that of Fe₂O₃ 6 wt%. The contents of about 20 wt % additives and 6 wt% Fe₂O₃ are known optimum ones to improve the reaction rates of Mg with H₂. Samples with compositions of 80 wt% Mg–14 wt% Ni–6 wt% Fe₂O₃ (named as Mg–14Ni–6Fe₂O₃), and 78 wt% Mg–14 wt% Ni–6 wt% Fe₂O₃–2 wt% CNT (named as Mg–14Ni–6Fe₂O₃–2CNT) were prepared by reactive mechanical grinding. The hydriding and dehydriding properties of these samples were then measured, and the effects of Ni, Fe₂O₃, and CNT addition on the hydriding and dehydriding rates of Mg-based alloys were investigated by comparing their hydrogen-storage properties with those of pure Mg and Mg–10 wt% Fe₂O₃.     

Improvement of hydrogen-storage properties of MgH2 by Ni,LiBH4, and Ti addition

In this work, differently from our previous work, MgH₂ instead of Mg was used as a starting material. Ni, Ti, and LiBH₄ with a high hydrogen-storage capacity of 18.4 wt% were added. A sample with a composition of MgH₂–10Ni–2LiBH₄–2Ti was prepared by reactive mechanical grinding. MgH₂–10Ni–2LiBH₄–2Ti after reactive mechanical grinding contained MgH₂, Mg, Ni, TiH_1.924, and MgO phases. The activation of MgH₂–10Ni–2LiBH₄–2Ti for hydriding and dehydriding reactions was not required. At the number of cycles, n = 2, MgH₂–10Ni–2LiBH₄–2Ti absorbed 4.09 wt% H for 5 min, 4.25 wt% H for 10 min, and 4.44 wt% H for 60 min at 573 K under 12 bar H₂. At n = 1, MgH₂–10Ni–2LiBH₄–2Ti desorbed 0.13 wt% H for 10 min, 0.54 wt% H for 20 min, 1.07 wt% H for 30 min, and 1.97 wt% H for 60 min at 573 K under 1.0 bar H₂. The PCT (Pressure–Composition–Temperature) curve at 593 K for MgH₂–10Ni–2LiBH₄–2Ti showed that its hydrogen-storage capacity was 5.10 wt%. The inverse dependence of the hydriding rate on temperature is partly due to a decrease in the pressure differential between the applied hydrogen pressure and the equilibrium plateau pressure with the increase in temperature. The rate-controlling step for the dehydriding reaction of the MgH₂–10Ni–2LiBH₄–2Ti at n = 1 was analyzed.     

Improvement in dye-sensitized solar cells employing TiO2 electrodes coated with Al2O3 by reactive direct current magnetron sputtering

A novel surface modification method was carried out by reactive dc magnetron sputtering to fabricate TiO₂ electrodes coated with Al₂O₃ for improving the performance of dye-sensitized solar cells (DSSCs). The Al₂O₃-coated TiO₂ electrodes had been characterized by X-ray photoelectron spectroscopy (XPS), scanning electron microscopy (SEM), UV–vis spectrophotometer, cyclic voltammetry (CV), and electrochemical impedance spectroscopy (EIS). The study results revealed that the modification to TiO₂ increases dye absorption amount, reduces trap sites on TiO₂, and suppresses interfacial recombination. The impact of sputtering time on photoelectric performance of DSSCs was investigated. Sputtering Al₂O₃ for 4 min on 5-μm thick TiO₂ greatly improves all cell parameters, resulting in enhancing the conversion efficiency from 3.93% to 5.91%. Further increasing sputtering time decreases conversion efficiency.     

Enhanced heterogeneous ferrioxalate photo-fenton degradation of reactive orange 4 by solar light

A combined homogeneous and heterogeneous photocatalytic decolourisation and degradation of a chlorotriazine Reactive azo dye Reactive Orange 4 (RO4) have been carried out using ferrous sulphate/ ferrioxalate with H₂O₂ and TiO₂-P25 particles. Solar/ferrous/H₂O₂/TiO₂-P25 and solar/ferrioxalate/H₂O₂/TiO₂-P25 processes are found to be more efficient than the individual photo-Fenton and solar/TiO₂-P25 processes. A comparison of these two processes with UV/ferrous/H₂O₂/TiO₂-P25 and UV/ferrioxalate/H₂O₂/TiO₂-P25 reveals that ferrioxalate is more efficient in solar light whereas ferrous ion is more efficient in UV light. The experimental parameters such as pH, initial H₂O₂, Fe²⁺, ferrioxalate and TiO₂-P25 concentration strongly influenced the dye removal rate in solar processes. The optimum operating conditions of these two combined processes are reported.     

Improvement in the hydrogen storage properties of Mg by mechanical grinding with Ni, Fe and V under H2 atmosphere

Mg-5wt%Ni-2.5wt%Fe-2.5wt%V (named Mg-5Ni-2.5Fe-2.5V) powder was prepared by reactive mechanical grinding using a planetary ball mill. The activation process, the changes in phase and microstructure with hydriding-dehydriding cycling, and the variations in the hydriding and dehydriding rates with temperature were investigated. The rate-controlling step for the dehydriding reaction of Mg-5Ni-2.5Fe-2.5V was analyzed by using a spherical moving boundary model. As the temperature increased from 473 K through 623 K, the initial hydrogen absorption rate under 12 bar H₂ decreased, while the hydrogen desorption rate under 1.0 bar H₂ increased.     

Preparation of In2O3:F thin films grown by spray pyrolysis technique

Transparent conducting fluorine doped indium oxide (In₂O₃:F) thin films have been deposited on Corning 7059 glass substrates by the spray pyrolysis technique. The structural, electrical, and optical properties of these films were investigated as a function of substrate temperature. The X-ray diffraction pattern of the films deposited at lower substrate temperature (T_s=300 °C) showed no peaks of In₂O₃:F. In the useful range for deposition (i.e. 425–600 °C), the orientation of the films was predominantly [400]. For the 4500 Å thick In₂O₃:F deposited with an F content of 10-wt%, the minimum sheet resistance was 120 Ω and average transmission in the visible wavelength rang (400–700 nm) was 88%.     

Synthesis and hydriding/dehydriding properties of nanosized sodium alanates prepared by reactive ball-milling

TiF₃-doped NaH/Al mixture was hydrogenated into Na₃AlH₆ and NaAlH₄ complex hydrides by reactive ball-milling at room temperature through the optimization of milling duration and hydrogen pressure. The analysis of the preparation of NaAlH₄ samples during reactive ball-milling process has been performed by XRD and TG/DSC. It has been found that Na₃AlH₆ was formed under 0.5 MPa hydrogen pressure and 30 h milling duration, while NaAlH₄ was formed under 0.8 MPa hydrogen pressure and 45 h milling duration. The process of preparing NaAlH₄ by ball-milling was found accomplished via two reaction steps, namely: (1) NaH + Al + H₂ → Na₃AlH₆ and (2) Na₃AlH₆ + Al + H₂ → NaAlH₄. As the hydrogen pressure and milling duration increase, the synthetic yield of NaAlH₄ and its corresponding dehydriding capacity are both increased. With increased hydrogen pressure (0.8-3 MPa) and milling duration (45-60 h), the cell volume of Na₃AlH₆ decreases while that of NaAlH₄ increases gradually. The abundance of Na₃AlH₆ phase decreases from 57.76 (x = 0.8, y = 45) to 8.69 wt.% (x = 3, y = 60), and the abundance of NaAlH₄ phase increases from 20.63 (x = 0.8, y = 45) to 86.50 wt.% (x = 3, y = 60). All the samples prepared in this way have fairly good activation behavior and fast hydriding/dehydriding reaction kinetics, which are capable of absorbing 4.26 wt.% hydrogen at 120 °C and desorbing 4.12 wt.% hydrogen at 150 °C, respectively. The improvement of hydriding/dehydriding properties is ascribed to the favorable microstructure and ultrafine particle features of nanosized NaAlH₄ formed during ball-milling at the optimum synthetic condition.     

Enhancement of the hydrogen storage characteristics of Mg by reactive mechanical grinding with Ni,Fe and Ti

Mg-10wt%Ni-5wt%Fe-5wt%Ti powder was prepared by reactive mechanical grinding using a planetary ball mill. The Mg-10wt%Ni-5wt%Fe-5wt%Ti powder exhibited high hydriding and dehydriding rates even at the first cycle, and its activation was completed after two hydriding–dehydriding cycles. After the reactive mechanical grinding, the particle size of the powder was reduced, as compared with those of the starting materials. The hydrogen storage properties were measured at temperatures of 473 K, 573 K and 623 K. The activated Mg-10wt%Ni-5wt%Fe-5wt%Ti powder absorbed 5.31 wt% and 5.51 wt% of hydrogen for 5 min and 1 h, respectively, at 573 K under 12 bar H₂. It desorbed 5.18 wt% of hydrogen at 573 K under 1.0 bar H₂ for 1 h. The initial hydrogen absorption rate increased when passing from 473 K to 573 K, but decreased at 623 K. The hydrogen desorption rate increased rapidly with increasing temperature from 473 K to 623 K. The hydrogen storage capacity was about 6.72 wt% at 573 K.     

Enhancement of hydrogen-storage performance of MgH2 by Mg2Ni formation and hydride-forming Ti addition

MgH₂, rather than Mg, was used as a starting material in this work. A sample with a composition of MgH₂–10Ni–4Ti was prepared by reactive mechanical grinding. Activation of the sample was completed after the first hydriding cycle. At n = 1, the sample desorbed 2.53 wt% H for 10 min, 3.99 wt% H for 20 min, 4.58 wt% H for 30 min, and 4.68 wt% H for 60 min at 593 K under 1.0 bar H₂. At n = 2, the sample absorbed 3.59 wt% H for 5 min, 4.55 wt% H for 25 min, and 4.60 wt% H for 45 min at 593 K under 12 bar H₂. The inverse dependence of the hydriding rate on the temperature in the initial stage and the normal dependence of the hydriding rate on the temperature in the later stage were discussed. The rate-controlling step for the dehydriding reaction of activated MgH₂–10Ni–4Ti was analyzed as the chemical reaction at the hydride/α-solid solution interface.     

Hydrogen storage properties of a Mg–Ni–Fe mixture prepared via planetary ball milling in a H2 atmosphere

A sample composition has been designed based on previously reported data. An 80 wt%Mg–13.33 wt%Ni–6.67 wt%Fe (referred to as Mg–13.33Ni–6.67Fe) sample exhibited higher hydriding and dehydriding rates after activation and a larger hydrogen storage capacity compared to those of other mixtures prepared under similar conditions. After activation (at n = 3), the sample absorbed 4.60 wt%H for 5 min and 5.61 wt%H for 60 min at 593 K under 12 bar H₂. The sample desorbed 1.57 wt%H for 5 min and 3.92 wt%H for 30 min at 593 K under 1.0 bar H₂. Rietveld analysis of the XRD pattern using FullProf program showed that the as-milled Mg–13.33Ni–6.67Fe sample contained Mg(OH)₂ and MgH₂ in addition to Mg, Ni, and Fe. The Mg(OH)₂ phase is believed to be formed through the reaction of Mg or MgH₂ with water vapor in the air. The dehydrided Mg–13.33Ni–6.67Fe sample after hydriding-dehydriding cycling contained Mg, Mg₂Ni, MgO, and Fe.     

Prontonic ceramic membrane fuel cells with layered GdBaCo2O5+x cathode prepared by gel-casting and suspension spray

In order to develop a simple and cost-effective route to fabricate protonic ceramic membrane fuel cells (PCMFCs) with layered GdBaCo₂O_5+x (GBCO) cathode, a dense BaZr_0.1Ce_0.7Y_0.2O_3−δ (BZCY7) electrolyte was fabricated on a porous anode by gel-casting and suspension spray. The porous NiO–BaZr_0.1Ce_0.7Y_0.2O_3−δ (NiO–BZCY7) anode was directly prepared from metal oxide (NiO, BaCO₃, ZrO₂, CeO₂ and Y₂O₃) by a simple gel-casting process. A suspension of BaZr_0.1Ce_0.7Y_0.2O_3−δ powders synthesized by gel-casting was then employed to deposit BaZr_0.1Ce_0.7Y_0.2O_3−δ (BZCY7) thin layer by pressurized spray process on NiO–BZCY7 anode. The bi-layer with 10 μm dense BZCY7 electrolyte was obtained by co-sintering at 1400 °C for 5 h. With layered GBCO cathode synthesized by gel-casting on the bi-layer, single cells were assembled and tested with H₂ as fuel and the static air as oxidant. An open-circuit potential of 0.98 V, a maximum power density of 266 mW cm⁻², and a low polarization resistance of the electrodes of 0.16 Ω cm² was achieved at 700 °C.     

Synthesis and electrochemical properties of lithium non-stoichiometric Li1+x(Ni1/3Co1/3Mn1/3)O2+δ prepared by a spray drying method

Lithium non-stoichiometric Li[Li_x(Ni_1/3Co_1/3Mn_1/3)_1−x]O₂ materials (0 ≤ x ≤ 0.17) were synthesized using a spray drying method. The electrochemical properties and structural stabilities of the synthesized materials were investigated. The synthesized materials exhibited a hexagonal structure in all the x-value and the lattice parameters of the materials were gradually decreased with increasing x-value due to an increasing amount of Ni³⁺ ions for charge compensation. The capacity retention ability and rate capability of the stoichiometric Li(Ni_1/3Co_1/3Mn_1/3)O₂ material were improved by increasing x-value, the so-called overlithiation. We found that the overlithiated materials could keep more structural integrity than the stoichiometric one during electrochemical cyclings, which could be one of reasons for a better electrochemical properties of the overlithiated materials.     

Electrochromic characteristics of fibrous reticulated WO3 thin films prepared by pulsed spray pyrolysis technique

The electrochromic (EC) behavior of fibrous reticulated WO₃ films prepared from ammonium tungstate precursor by pulsed spray pyrolysis method was investigated. All the films were prepared using identical technological parameters and a thorough investigation of the electrochromic properties of the films deposited at 300 °C is reported. The structural properties were studied by X-ray diffraction (XRD) and scanning electron microscopy (SEM). The electrochromic and optical properties were measured using cyclic voltammetry and ultraviolet (UV)-visible spectrophotometry. The films are amorphous and have a fibrous reticulate-like morphology having micron-size circular rings. The films show high transparency in the visible range and the optical band gap energy is about 3.1 eV. Electrical measurements show that the resistivity monotonically decreases as temperature increases, which indicates thermal hopping transport. The activation energy for hopping transport is of the order 4×10⁻⁴ eV. The electrochromic coloration efficiency (CE) is found to be 34 cm²/C at 630 nm.     

Interactions of refractory materials with molten gasifier slags

The current study focuses on the analysis of sessile-drop interfacial reactions between two synthetic slags (based on average ash chemistries of coal and petcoke feedstock) and two refractory materials (90 wt% Cr₂O₃-10 wt% Al₂O₃ and 100 wt% Al₂O₃), using a Confocal Scanning Laser Microscope (CSLM). Ground slag samples (less than 325 mesh) were placed at specific microstructure locations on refractory substrates and heated to 1500 °C in an atmosphere of CO/CO₂ gas mixture (volume ratio = 1.8), using a gold-image heating chamber. Cross-sections of the slag/refractory interface indicated unique slag penetration into preferred areas of the refractory and grain dissolution into the slag which promoted spalling of the refractory. Initially, the slag attacked both grain boundaries and fine microstructure areas, freeing alumina grains into the slag. The formation of VO_x-based crystalline material in the petcoke slag was found to alter the liquid composition. Chemical spalling of Cr-containing crystal layer also facilitated degradation of the refractory.     

Stabilized zirconia-based sensor utilizing SnO2-based sensing electrode with an integrated Cr2O3 catalyst layer for sensitive and selective detection of hydrogen

A highly selective hydrogen (H₂) sensor has been successfully developed by using an yttria-stabilized zirconia (YSZ)-based mixed-potential-type sensor utilizing SnO₂ (+30 wt.% YSZ) sensing electrode (SE) with an intermediate Al₂O₃ barrier layer which was coated with a catalyst layer of Cr₂O₃. The sensor utilizing SnO₂ (+30 wt.% YSZ)-SE was found to be capable of detecting H₂ and propene (C₃H₆) sensitively at 550 °C. In order to enhance the selectivity towards H₂, a selective C₃H₆ oxidation catalyst was employed to minimize unwanted responses caused by interfering gases. Among the examined metal oxides, Cr₂O₃ facilitated the selective oxidation of C₃H₆. However, the addition or lamination of Cr₂O₃ to SnO₂ (+30 wt.% YSZ)-SE was found to diminish the sensing responses to all examined gases. Therefore, an intermediate layer of Al₂O₃ was sandwiched between the SE layer and the catalyst layer to prevent the penetration of Cr₂O₃ particles into the SE layer. The sensor using SnO₂ (+30 wt.% YSZ)-SE coated with a catalyst layer of Cr₂O₃ as well as an intermediate layer of Al₂O₃ exhibited a sensitive response toward H₂, with only minor responses toward other examined gases at 550 °C under humid conditions (21 vol.% O₂ and 1.35 vol.% H₂O in N₂ balance). A linear relationship was observed between sensitivity and H₂ concentration in the range of 20–800 ppm on a logarithmic scale. The results of sensing performance evaluation and polarization curve measurements indicate that the sensing mechanism is based on the mixed-potential model.     

Synthesis and electrochemical properties of olivine LiFePO4 prepared by a carbothermal reduction method

LiFePO₄/C composite cathode material was prepared by carbothermal reduction method, which uses NH₄H₂PO₄, Li₂CO₃ and cheap Fe₂O₃ as starting materials, acetylene black and glucose as carbon sources. The precursor of LiFePO₄/C was characterized by differential thermal analysis and thermogravimetry. X-ray diffraction (XRD), scanning electron microscopy (SEM) micrographs showed that the LiFePO₄/C is olivine-type phase, and the addition of the carbon reduced the LiFePO₄ grain size. The carbon is dispersed between the grains, ensuring a good electronic contact. The products sintered at 700 °C for 8 h with glucose as carbon source possessed excellent electrochemical performance. The synthesized LiFePO₄ composites showed a high electrochemical capacity of 159.3 mAh g⁻¹ at 0.1 C rate, and the capacity fading is only 2.2% after 30 cycles.     

Energy efficient simultaneous oxidative conversion and thermal cracking of ethane to ethylene using supported BaO/La2O3 catalyst in the presence of limited O2

An energy efficient conversion of ethane to ethylene involving simultaneous oxidative conversion (which is exothermic) and thermal cracking (which is endothermic) reactions of ethane in the presence of steam (steam/C₂H₆ mol RATIO=1.0) and limited O₂ (C₂H₆/O₂ mol ratio 4.0) over a BaO-promoted La₂O₃ supported on low surface area macroporous silica-alumina commercial catalyst carrier has been thoroughly investigated. Influence of various process parameters such as temperature (700–850°C), C₂H₆/O₂ feed ratio (4.0–8.0) and space velocity (50,000–200,000 cm³ g⁻¹ h⁻¹) on the conversion, product selectivity and net heat of reactions in the process has also been studied. At all the process conditions, there was no coke deposition on the catalyst. High selectivity ( 85%) for C₂₊ olefins (at 50–60% conversion) can be obtained in the process at a low contact time (<10 ms), particularly for the higher C₂H₆/O₂ ratios ( 6.0) and temperatures ( 800°C). The process exothermicity is decreased appreciably with increasing the temperature and/ or the C₂H₆/O₂ ratio. The net heat of reaction in the process can be controlled by manipulating the C₂H₆/O₂ ratio and reaction temperature. Also, because of simultaneously occurring endothermic and exothermic reactions, the process is highly energy efficient and non-hazardous.