Microstructure and hydrogen storage properties of (Ti0.32Cr0.43V0.25) + x wt% La (x = 0–10) alloys

The composite alloy of Ti_0.32Cr_0.43V_0.25 with x wt% La (where x = 0–10) was prepared by arc melting technique. The effect on hydrogen storage capacity, flatness of the plateau pressure, and residual hydrogen was investigated in La added Ti_0.32Cr_0.43V_0.25. Crystalline phase and microstructure of the prepared composite alloy were investigated and characterized by XRD, SEM and TEM. The crystal structure was refinement using Rietveld analysis. The effective hydrogen storage capacity of the composite alloy was found comparable to the parent alloy, when 5 wt% La was added. The effective hydrogen capacity (∼2.31 wt%) was close to that of the parent alloy (2.35 wt%) and the plateau slope was significantly improved from 30.5 of the parent alloy to 14.6. Appropriate mechanisms associated with the improved flatness by the La addition has been discussed in terms of the refined crystalline structure. Using TG/DTA method we have shown the differences in the interaction of residual hydrogen with the BCC phase of both parent alloy and 5 wt % La mixed alloy.     

Start-up behaviors of a H2SO4–H2O distillation column for the 50 NL H2/H sulfur–iodine cycle

The sulfur–iodine (SI) cycle to produce hydrogen from water requires a multistage distillation column to concentrate a sulfuric acid solution. To design a concentration process of a sulfuric acid solution that can be applied to the cycle, its static and dynamic simulation is essentially demanded. A 50 NL H₂/h scale SI test facility to be operated under a pressurized environment has been constructed in Korea. This study focuses on the sulfuric acid multi-stage distillation column (SAMDC-50L) for the 50 NL H₂/h SI test facility. The SAMDC-50L was designed and installed in 2012. Based on the design specifications and operation method, a start-up behavior of the SAMDC-50L has been analyzed using the simulation code “KAERI-DySCo”. As a result of the start-up dynamic simulation, it is confirmed that the SAMDC-50L will approach to the steady state value within 30,000 s to fulfill the hydrogen production rate of 50 NL H₂/h. On the other hand, it is expected that the operation time approaching a steady state decreases with an increase in the set point of the condenser temperature until a dew point of the top vapor product and the time required for the transition to the complete steady state is increased with an increasing reflux ratio and reboiler hold-up.     

Effect of alumina on the enhancement of hydrogen production and the reduction of hydrogen peroxide in the γ-radiolysis of pure water and 0.4 M H2SO4 aqueous solution

The H₂ and H₂O₂ produced by ⁶⁰Co γ-radiation at room temperature were measured in pure water and 0.4 M H₂SO₄ aqueous solution with alumina powder. By increasing the addition of alumina powder, a strong reduction of H₂O₂ concentrations in the solutions was obtained, and the final product H₂ yields were correspondingly enhanced. These enhancement and reduction effects were diminished in the subsequent γ-radiation when irradiated alumina powder was used. The effects were reversibly restored by washing the irradiated powder with purified water. In 0.4 M H₂SO₄ solution with alumina powder, the H₂ yields increased by increasing the absorbed dose rate in the region of 1-5 kGy/h. The radiation-enhanced H₂ production correlated with the reduction of H₂O₂ concentration could be brought about by the reduction of H₂O₂ molecules and OH radicals in the solutions due to alumina powder.     

Effects of alumina powder characteristics on H2 and H2O2 production yields in γ-radiolysis of water and 0.4 M H2SO4 aqueous solution

The effects of powder characteristics on H₂ and H₂O₂ productions in ⁶⁰Co γ-radiolysis were studied in pure water and in 0.4 M H₂SO₄ aqueous solutions containing alumina powders. In 0.4 M H₂SO₄ solution, the H₂ yields strongly depended on alumina structures and decreased in the order of α > θ > γ-alumina, although the specific surface areas increased as α < θ < γ. The yields increased with increasing specific surface area when compared among α-alumina. In pure water, similar dependence was observed but not as strong as that for 0.4 M H₂SO₄ solution. The H₂O₂ yields were strongly decreased by adding the alumina powders in both water and 0.4 M H₂SO₄ aqueous solution, although the amounts of decrease were almost neither correlated with specific surface areas nor structures. The enhancing H₂ production was discussed in terms of the electron supply from alumina to aqueous solution as well as the adsorption of OH radicals on alumina surfaces.     

An investigation on the hydrogen storage properties and reaction mechanism of the destabilized MgH2–Na3AlH6 (4:1) system

A novel hydrogen storage composite system, MgH₂–Na₃AlH₆ (4:1), was prepared by mechanochemical milling, and its hydrogen storage properties and reaction mechanism were studied. Temperature-programmed desorption results showed that a mutual destabilization effect exists between the components. First, Na₃AlH₆ reacts with MgH₂ to form a perovskite-type hydride, NaMgH₃, Al, and H₂ at a temperature of about 170 °C, which is about 55 °C lower than the decomposition temperature of as-milled Na₃AlH₆. Then, at a temperature of about 275 °C, the as-formed Al can destabilize MgH₂ to form the intermetallic compound Mg₁₇Al₁₂, which is accompanied by the self-decomposition of the residual MgH₂. This temperature is about 55 °C lower than the decomposition temperature for as-milled MgH₂. Furthermore, when heated up to 345 °C, NaMgH₃ starts to decompose into NaH, Mg, and H₂, which is followed by the decomposition of NaH at a temperature of about 370 °C. Rehydrogenation processes show that Mg₁₇Al₁₂ and NaMgH₃ are fully reversible. It is believed that the Mg₁₇Al₁₂ and NaMgH₃ formed in situ provide synergetic thermodynamic and kinetic destabilization, leading to the dehydrogenation of MgH₂, which is responsible for the distinct reduction in the operating temperatures of the as-prepared MgH₂–Na₃AlH₆ (4:1) composite system.     

Improved dehydrogenation properties of the combined Mg(BH4)2·6NH3–nNH3BH3 system

A combined strategy via mixing Mg(BH₄)₂·6NH₃ with ammonia borane (AB) is employed to improve the dehydrogenation properties of Mg(BH₄)₂·6NH₃. The combined system shows a mutual dehydrogenation improvement in terms of dehydrogenation temperature and hydrogen purity compared to the individual components. A further improved hydrogen liberation from the Mg(BH₄)₂·6NH₃–6AB is achieved with the assistance of ZnCl₂, which plays a crucial role in stabilizing the NH₃ groups and promoting the recombination of NH^δ+?HB^δ−. Specifically, the Mg(BH₄)₂·6NH₃–6AB/ZnCl₂ (with a mole ratio of 1:0.5) composite is shown to release over 7 wt.% high-pure hydrogen (>99 mol%) at 95 °C within 10 min, thereby making the combined system a promising candidate for solid hydrogen storage.     

Nanospheres and nanorods structured Fe2O3 and Fe2−xGaxO3 photocatalysts for visible-light mediated (λ ≥ 420 nm) H2S decomposition and H2 generation

This article reports our investigation on H₂ generation from visible light (λ ≥ 420 nm) photodecomposition of H₂S by nanomaterial catalysts, α-Fe₂O₃ and its chemically modified Fe_2−xGa_xO₃ (Ga substitution at x = 0.6, FeGaO₃-I and x = 1.0, FeGaO₃-II). Simple template-free hydrothermal technique was employed to synthesize the three photocatalysts. XRD study reveals rhombohedral nanocrystalline structure and FESEM shows nanospheres morphology for Fe₂O₃ and nanosticks/nanorods for both FeGaO₃-I, and FeGaO₃-II. In H₂ generation, Fe₂O₃ and FeGaO₃-II perform moderate and almost same activities in the fresh and used conditions (quantum yield, QY = 6.0–6.8% at 550 nm). Contrarily, fresh FeGaO₃-I exhibits a greater activity (11.2% QY) and the activity is further enhanced (QY = 15.3%) on regeneration and reuse. The intricacy, as resolved by XRD and FESEM, appears to take place through morphology transformation. The present work, thus, successfully demonstrates H₂ generation from H₂S by nanostructured photocatalysts involving morphology dependent activity enhancement.     

The computational study of the “inversion substitution” reactions CX3Br + O2 → CX3O2 + Br (X = H,F)

The kinetic parameters for the “inversion substitution” reactions of Br-containing fire suppressants CH₃Br and CF₃Br with molecular oxygen CX₃Br + O₂ → CX₃O₂ + Br (X = H, F) have been obtained on the basis of computational study carried out by quantum chemistry methods and transition state theory (TST). The DFT/B3LYP approach has been used to obtain molecular structures and vibrational frequencies and CCSD(T) method with additive corrections at MP2 and SODFT levels have been applied in order to calculate reaction enthalpies and activation barriers. Activation barrier for the substitution reaction CH₃Br + O₂ → CH₃O₂ + Br was found to be (53.3 kcal/mol) close to the endoergicity (51.2 kcal/mol) of bimolecular abstraction CH₃Br + O₂ → CH₂Br + HO₂ which means that this “inversion substitution” should be considered as a competing process in the oxidation initiation of bromine containing substances. The results of these calculations together with the earlier results have allowed us to build the correlation of Evans–Polanyi type between the activation barrier and reaction enthalpy for “inversion substitution” reactions CH₃X + O₂ → CH₃O₂ + X. For bromotrifluoromethane CF₃Br (Halon-1301) the barrier of “inversion substitution” was found to be of 86 kcal/mol that is higher by about 15 kcal/mol as compared with unimolecular decay CF₃Br → CF₃ + Br barrier. This makes negligible the role of bimolecular substitution reaction for kinetics of CF₃Br in oxygen environment. The TST calculations of the rate constants and their temperature dependence for the direct and reverse “inversion substitution” reactions have been carried out within the temperature interval of 273–2000 K.     

Preparation and evaluation of Ca3−xBixCo4O9−δ (0< x ≤ 0.5) as novel cathodes for intermediate temperature-solid oxide fuel cells

The misfit compounds Ca_3−xBi_xCo₄O_9−δ (x = 0.1–0.5) were successfully synthesized via conventional solid state reaction and evaluated as cathode materials for intermediate temperature-solid oxide fuel cells. The powders were characterized by X-ray diffraction, scanning emission microscopy, X-ray photoelectron spectroscopy, thermogravimetry analysis and oxygen-temperature programmed desorption. The monoclinic Ca_3−xBi_xCo₄O_9−δ powders exhibit good thermal stability and chemical compatibility with Ce_0.8Sm_0.2O_2−γ electrolyte. Among the investigated single-phase samples, Ca_2.9Bi_0.1Co₄O_9−δ shows the maximal conductivity of 655.9 S cm⁻¹ and higher catalytic activity compared with other Ca_3−xBi_xCo₄O_9−δ compositions. Ca_2.9Bi_0.1Co₄O_9−δ also shows the best cathodic performance and its cathode polarization resistance can be further decreased by incorporating 30 wt.% Ce_0.8Sm_0.2O_2−γ. The maximal power densities of the NiO/Ce_0.8Sm_0.2O_2−γ anode-supported button cells fabricated with the Ce_0.8Sm_0.2O_2−γ electrolyte and Ca_2.9Bi_0.1Co₄O_9−δ + 30 wt.% Ce_0.8Sm_0.2O_2−γ cathode reach 430 and 320 mW cm⁻² at 700 and 650 °C respectively.     

NMR spectroscopic and thermodynamic studies of the etherate and the α, α′, and γ phases of AlH3

Aluminum hydride (alane; AlH₃) has been identified as a leading hydrogen storage material by the US Department of Energy. With a high gravimetric hydrogen capacity of 10.1 wt.%, and a hydrogen density of 1.48 g/cm³, AlH₃ decomposes cleanly to its elements above 60 °C with no side reactions. This study explores in detail the thermodynamic and spectroscopic properties of AlH₃; in particular the α, α′ and γ polymorphs, of which α′-AlH₃ is reported for the first time, free from traces of other polymorphs or side products. Thermal analysis of α-, α′-, and γ-AlH₃ has been conducted, using DSC and TGA methods, and the results obtained compared with each other and with literature data. All three polymorphs were investigated by ¹H MAS-NMR spectroscopy for the first time, and their ²⁷Al MAS-NMR spectra were also measured and compared with literature values. AlH₃·nEt₂O has also been studied by ¹H and ²⁷Al MAS-NMR spectroscopy and DSC and TGA methods, and an accurate decomposition pathway has been established for this adduct.     

Material properties and empirical rate equations for hydrogen sorption reactions in 2 LiNH2–1.1 MgH2–0.1 LiBH4–3 wt.% ZrCoH3

2 LiNH₂–1.1 MgH₂–0.1 LiBH₄–3 wt.% ZrCoH₃ is a solid state hydrogen storage material with a hydrogen storage capacity of up to 5.3 wt.%. As the material shows sufficiently high desorption rates at temperatures below 200 °C, it is used for a prototype solid state hydrogen storage tank with a hydrogen capacity of 2 kWh_el that is coupled to a high temperature proton exchange membrane fuel cell. In order to design an appropriate prototype reactor, model equations for the rate of hydrogen sorption reactions are required. Therefore in the present study, several material properties, like bulk density and thermodynamic data, are measured. Furthermore, isothermal absorption and desorption experiments are performed in a temperature and pressure range that is in the focus of the coupling system. Using experimental data, two-step model equations have been fitted for the hydrogen absorption and desorption reactions. These empirical model equations are able to capture the experimentally measured reaction rates and can be used for model validation of the design simulations.     

The adsorption and dissociation of H2O on TiO2(110) and M/TiO2(110) (M = Pt,Au) surfaces–A computational investigation

The adsorption and dissociation of H₂O on clean TiO₂(110) and metal-deposited M/TiO₂(110) (M = Pt and Au) surfaces were studied by performing calculations of periodic density-functional theory. M/TiO₂(110) surfaces catalytically decompose H₂O with barriers (decreased by ca. 15–19 kcal/mol) much smaller than for their clean TiO₂(110) counterparts. The Au-deposited TiO₂ surface has the least energy barrier (ca. 3.5 kcal/mol less than the Pt analogue), explicable with a Bader charge analysis.     

Structure of V-doped Pdn (n = 2–12) clusters and their ability for H2 dissociation

The structure and stability of V-doped Pd_n (n = 2–12) clusters as well as their ability for hydrogen dissociation are analyzed using a successive growth algorithm coupled with density functional theory (DFT) computations. From the structural point of view, the lowest energy structures of these clusters are three-dimensional with exohedral geometries for n = 2–7 whereas endohedral for n = 8 onward. From their second-order energy differences, Pd₄V and Pd₁₀V are found to be the most stable ones. Among the Pd_nV(H₂) complexes, Pd₆V2H possesses the highest stability, as it is supported by the chemisorption energy, the vertical ionization potential (VIP), and the vertical electron affinity (VEA), respectively. Most importantly, the hydrogen dissociation pathway on Pd_nV clusters with n = 3, 4 and 10–12 shows that these clusters are rigid and suitable to dissociate H₂ while for n = 5–9 the structure of the clusters changes. The H₂ dissociation process on Pd_nV clusters with n = 8, 10, and 11 carries out barrierless.     

Performance and stability of nano-structured Pd and Pd0.95M0.05 (M = Mn,Co, Ce,and Gd) infiltrated Y2O3–ZrO2 oxygen electrodes of solid oxide electrolysis cells

Nano-structured Pd infiltrated and Pd_0.95M_0.05 (M = Mn, Co, Ce, and Gd) co-infiltrated Y₂O₃–ZrO₂ (YSZ) electrodes are studied as the oxygen electrodes of solid oxide electrolysis cells (SOECs). The infiltrated Pd-YSZ electrodes show good electrocatalytic activity for the oxygen evolution reaction. For example, the electrode polarization resistance (R_E) for 2.0 mg cm⁻² Pd infiltrated YSZ is 0.36 Ω cm⁻² at 800 °C. R_E is not significantly affected by co-infiltrating Pd with Mn and Co, but is enhanced by co-infiltration of Ce and Gd. The co-infiltration of low concentrations of metals in particular Co, Ce and Gd significantly enhances the microstructure and performance stability of the Pd-YSZ electrodes. The results demonstrate that the addition of dopants to the Pd in the form of either an alloy (Co) or a separate phase (Ce and Gd) is beneficial to enhance the performance and stability of Pd based oxygen electrodes of SOECs.     

Releasing 9.6 wt% of H2 from Mg(NH2)2–3LiH–NH3BH3 through mechanochemical reaction

Ball milling the mixture of Mg(NH₂)₂, LiH and NH₃BH₃ in a molar ratio of 1:3:1 results in the direct liberation of 9.6 wt% H₂ (11 equiv. H), which is superior to binary systems such as LiH–AB (6 equiv. H), AB–Mg(NH₂)₂ (No H₂ release) and LiH–Mg(NH₂)₂ (4 equiv. H), respectively. The overall dehydrogenation is a three-step process in which LiH firstly reacts with AB to yield LiNH₂BH₃ and LiNH₂BH₃ further reacts with Mg(NH₂)₂ to form LiMgBN₃H₃. LiMgBN₃H₃ subsequently interacts with additional 2 equivalents of LiH to form Li₃BN₂ and MgNH as well as hydrogen.     

Investigation of MBH4–VCl2, M = Li,Na or K

Systematic investigations of MBH₄−VCl₂, M = Li, Na, or K, 2:1 or 3:1, samples prepared by mechano-chemistry and different milling time in order to gain insight in the phase stability and search for novel borohydrides. The samples were investigated using powder X-ray diffraction and Raman spectroscopy. Subsequently, the samples were exposed to heat treatment and investigated by in-situ synchrotron radiation powder X-ray diffraction (SR-PXD). These studies reveal formation of numerous compounds during decomposition of the samples, which contrasts with previous investigations. In several cases the formed compounds were in a less well-crystalline state, which did not allow identification. One of the unidentified compounds was observed both in the LiBH₄−VCl₂ and NaBH₄−VCl₂ systems and appeared to decompose at T ∼ 190 °C and is assumed to be a new vanadium borohydride. Crystalline Li₂VCl₄ was observed, but a major fraction of the decomposition products appeared to be amorphous. The KBH₄−VCl₂ system revealed formation of well-crystalline solid solutions of K(BH₄)_1−xCl_x.     

Pd–Ag thin film membrane for H2 separation. Part 2. Carbon and oxygen diffusion in the presence of CO/CO2 in the feed and effect on the H2 permeability

The effect of CO and CO₂ on the performance and stability of Pd–Ag thin film membranes prepared by electroless plating deposition (EPD) was investigated, observing the presence of dissociation to carbon and oxygen which slowly diffuse in the membrane influencing also H₂ permeability. The effect of the two carbon oxides was investigated both separately and combined in the 400–450 °C temperature range over long-term cumulative experiments (up to over 350 h) on a membrane that already worked for over 350 h in H₂ or H₂–N₂ mixtures. An increase of the H₂ permeation flux was observed feeding only CO₂ in the range 10–20%. This effect was interpreted as deriving from the facilitated H₂ flux caused from oxygen diffusion (deriving from CO₂ dissociation) in the membrane. CO induces instead a partial inhibition on the H₂ flux deriving from the negative effect of CO competitive chemisorption as well as C diffusion in the membrane, which overcome the positive effect associated to oxygen diffusion in the membrane. Carbon and oxygen diffuse through the membrane with a rate two order of magnitude lower than hydrogen, and recombinate at the permeate side forming CO, CO₂ and CH₄ which amount increases with time-on-stream. The effect is reversible and not associated with the creation of cracks or defects in the membrane, as supported by leak tests.     

Preparation and characterization of La0.9Sr0.1Ga0.8Mg0.2O3 − δ thin film on the porous cathode for SOFC

A dense and crack-free La_0.9Sr_0.1Ga_0.8Mg_0.2O_3 − δ thin film has been prepared by RF magnetron sputtering. The XRD, FESEM, XPS and four-probe technique are employed to characterize the La_0.9Sr_0.1Ga_0.8Mg_0.2O_3 − δ film. Results show that after annealing at 1000 °C, the La_0.9Sr_0.1Ga_0.8Mg_0.2O_3 − δ film presents a polycrystalline perovskite structure with grain size of 100–300 nm. XPS data show that both La and Ga are in their +3 state. Sr element has two chemical states which are related to Sr²⁺ in the perovskite lattice and SrO_1 − δ suboxide. The O 1s spectrum also shows two chemical states which can be assigned to molecularly adsorbed O₂ species and O²⁻ in the lattice. The electrical conductivity reaches to 0.093 S cm⁻¹ at 800 °C. The microstructure and conductivity analysis indicates that the La_0.9Sr_0.1Ga_0.8Mg_0.2O_3 − δ thin film prepared by RF magnetron sputtering is suitable for intermediate temperature Solid oxide fuel cell.     

Characterization of layered perovskite oxides NdBa1−xSrxCo2O5+δ (x = 0 and 0.5) as cathode materials for IT-SOFC

The crystal structure, thermal expansion, and electrochemical properties of the layered perovskite series NdBa_1−xSr_xCo₂O_5+δ (x = 0 and 0.5) were investigated to study the effects of substituting Sr for Ba on a layered perovskite oxide.