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NaAlH4 was mechano-chemically synthesized with high energy ball-milling method. The effect of synthesis conditions such as milling time, H2 pressure, chloride catalysts, and solvents was investigated to enhance the synthesis of NaAlH4. Among the chloride catalysts, TiCl4 showed the highest H2 pressure decrease which means the highest NaH conversion to NaAlH4. Furthermore, when the NaAlH4 was synthesized with THF solvent, it exhibited the higher H2 pressure decrease than that of sample prepared without THF solvent. This is mainly due to the synergy effect of TiCl4 catalyst and THF solvent.

The Sulfur-Iodine thermochemical hydrogen production process (SI process) consists of the Bunsen reaction section, the H2SO4 decomposition section and the HI decomposition section. The HIx solution (HI-I2-H2O) could be recycled to Bunsen reaction section from the HI decomposition section in the operation of the integrated SI process. The phase separation characteristic of the Bunsen reaction using the HIx solution was similar to that of SO2-I2-H2O system. However, the amount of produced H2SO4 phase was too small. To solve this problem, the study was carried out by the pressurized continuous Bunsen reaction. Bunsen reactions were performed at variation of feed rate of SO2/O2 gas in 3 bar of atmosphere. Also, it was performed to check the effects of the residence time in the reservoir on the characteristics of Bunsen products. As the results, the concentration of H2SO4 and HI in Bunsen products was increased with increasing the amounts of SO2. When the residence time in the reservoir increased, the concentration of H2SO4 and HI in HIx phase was decreased by reverse Bunsen reaction.

The Sulfur-Iodine process is in need of catalytic reactor for HI decomposition because the HI decomposition reaction rate is very slow. Nickel as an alternative catalyst for platinum was investigated in this study. Al2O3 supported Ni catalysts were prepared by impregnation method. Ni amounts loaded over Al2O3 were in the range of 0.1~20 wt. %. HI decompositions were carried out in the temperature range of 573 ~ 773 K using the fixed-bed quartz reactor. The difference of catalysts before and after the reaction was analyzed using BET, CO/H2 chemisorption, XRD, XRF and SEM. It was confirmed by XRD and SEM-EDX analysis that Ni was converted to NiI2 during the HI decomposition. Catalyst deactivation due to the formation of NiI2 leads to a reduction of HI conversion. Although Ni of catalyst converted to NiI2, HI decomposition with low loading (up to 3 wt. %) catalyst showed a little decrease of HI conversion. However, with more than 5 wt. % catalyst, the initial HI conversion was considerably decreased. In the particular case of 20 wt. %, the initial conversion was increased close to 60 %, which is higher than 20 % as an equilibrium conversion at 723 K. These results showed that Ni had not only a catalytic function for HI decomposition, but also function as a sorbent to absorb I2 produced from HI.

Ni (hydr)oxide is a promising and inexpensive material for oxygen evolution reaction (OER) catalysts and is known to dramatically increase the activity when used with Fe. Herein, we basified a Ni(II) solution and coated layered Ni(OH)2 on Ni coins to prepare a template with high stability and activity. To evaluate the stability and catalytic activity during high-current-density operation, we analyzed the electrochemical and physicochemical properties before and after constant current (CC) operation. The electrode with a Ni(OH)2 surface exhibited higher initial activity than that with a NiO surface; however, after the OER operation at a high-current density, degradation occurred owing to structural destruction. The activity of the electrodes with a NiO surface improved after the CC operation because of the changes on the electrode-surface caused by the CC operation and the subsequent Fe incorporation from the Fe impurity in the electrolyte. After confirming the improvement in activity due to Fe, we prepared NiFe-oxide electrodes with improved catalytic activity and optimized the Ni precursor and Fe loading solution concentrations. The Ni-Fe oxide electrode prepared under the optimal concentrations exhibited an overpotential of 287 mV at a current density of 10 mA/cm2, and a tafel slope of 37 mV dec−1, indicating an improvement in the OER activity. [ABSTRACT FROM AUTHOR]

Highly ordered TiO2 nanotubes (TNTs) decorated with a series of lanthanide ions (Ln3+ = Ho3+, Tb3+, Eu3+, Yb3+, and Er3+) were prepared through an electrochemical process and anodization. The composition, structure, and chemical bond of the as-prepared photocatalysts were characterized through scanning electron microscopy, X-ray diffraction, X-ray photoelectron spectroscopy, ultraviolet photoelectron spectroscopy, and ultraviolet diffuse reflectance spectroscopy. Furthermore, the electrochemical characteristics of the catalysts were analyzed and photoelectrochemical properties were investigated through water splitting. All samples were prepared in the anatase phase without changing the crystal structure. The holmium-doped TNT photocatalyst exhibited the best performance with a hydrogen evolution rate of 90.13 μmol cm−2h−1 and photoconversion efficiency of 2.68% (0 V vs. RHE). Photocatalytic efficiency increased because of the expansion of the absorption wavelength range attributed to the appropriate positioning of the band structure and reduced electron/hole pair recombination resulting from the unhindered electron movement. This study demonstrated the preparation of high-potential solar-active photocatalysts through the synergetic effects of the work function, band edge, and bandgap changes caused by the series of lanthanide combinations with TNTs. [ABSTRACT FROM AUTHOR]

Mg[Fe.sub.2][O.sub.4] samples were prepared by high-temperature thermal decomposition (HTTD), sol-gel, and solid-state reaction methods. The samples (a) prepared by HTTD, (b) annealed at 800[degrees]C prepared by sol-gel method under Ar atmosphere, and (c) annealed at 1100[degrees]C prepared by a solid-state reaction method have the inverse cubic spinel structure [((Fe).sub.A][[MgFe].sub.B][O.sub.4]) with a space group of Fd3m. The saturation magnetization ([M.sub.s]) and coercivity ([H.sub.c]) at room temperature are found to be 42.2, 44.2, and 53.3 emu/g and 1.2, 81.6, and 94.1 Oe, respectively. The Mossbauer spectra of all samples have been obtained at room temperature and the sample prepared by the HTTD method was measured at various temperatures ranging from 4.2 K to 300 K. The Mossbauer spectrum of the sample prepared by the HTTD method shows superparamagnetic behavior at room temperature and the Mossbauer spectra of the other samples show ferrimagnetic state of six-line shapes having the hyperfine field ([H.sub.f]) values of 432 ~ 452 kOe for the A sites and 466 ~ 483 kOe for the B sites. The linewidth and the hyperfine field of Mossbauer spectra is broadened and reduced, respectively, which is reduced the particle sizes. Index Terms--High-temperature thermal decomposition (HTTD), Magnesium ferrites, Mossbauer spectroscopy, superparamagnetism.