Zheng Xueping

Effect of Additives on the Reversibility of Lithium Alanate (LiAlH4)

Abstract The effect of various catalysts, such as Ti, Ni, Fe, Ce(SO 4 ) 2 and LaCl 3 , on the reversibility of LiAlH 4 was studied by Pressure-Content-Temperature (PCT) experiments. The result indicates that doping induces a marked decrease in the rate of hydrogen release. In addition, doping additives obviously decreases the initial temperature of LiAlH 4 of hydrogen release except for doping with LaCl 3 . However, at the same time, the amount of hydrogen release also decreases. In the study on the hydrogen absorption of LiAlH 4 doped with 1mol% Ni, 1mol% Ti, 1 mol% Ce(SO 4 ) 2 and 1mol%LaCl 3 at 180 °C under about 8 MPa, it has been found that the sample doped with 1 mol% Ni presents the largest hydrogen absorption amount with about 0.97wt%.

Influences of Y2O3 Doping on Hydrogen Release Property of LiAlH4

Abstract The dehydrogenation properties of LiAlH4 doped with Y2O3 were investigated by PCT (Pressure-Composition-Temperature) equipment. The results show that with the increase of amount of Y2O3, the dehydrogenation amount of LiAlH4 increases, however, when the doping amount reaches a certain value, the hydrogen release amount decreases with the increase of doping amount. Compared to the LiAlH4 sample, the dehydrogenation starting time of the samples doped with Y2O3 is significantly brought forward. In addition, it can be found that the dehydrogenation rates of all the doped samples are higher than that of the original sample. The change trends of the dehydrogenation rates of all the doped samples are similar in the whole dehydrogenation process, namely, with the extension of time, the dehydrogenation rates increase firstly, and then decrease gradually.

Effect of F−1 on the Hydrogen Release Properties of NaAlH4 and LiAlH4

Abstract This study mainly analyzed the effect of NaF and LiF on the hydrogen release properties of NaAlH 4 and LiAlH 4 by PCT (pressure-composition-temperature) apparatus. The results show that doping with NaF causes an obvious increase of the hydrogen release amount of NaAlH 4 except for the doping with 0.5 mol%, 4 mol% NaF. In addition, the doping with NaF induces an increase of the hydrogen release rate in the first stage. Among all the samples doped with NaF, the sample doped with 1mol% NaF presents the optimal hydrogen release properties with the largest hydrogen release amount and the fastest hydrogen release rate. Comparatively, the results from the study on the LiAlH 4 doped with LiF show that doping with LiF decreases obviously the hydrogen release amount of LiAlH 4 .

Effect of Oxide Particle Size on Electron Emission and Vacuum Arc Characteristic of Mo-La2O3 Cathode

Abstract A nanocomposite Mo-4wt% La2O3 cathode was prepared by a high-energy ball-milling and hot pressing technique. The sizes of lanthana particles in the nanocomposite Mo-La2O3 cathode are less than 100 nm; in contrast, the sizes of thoria particles are about 1∼2 μm in a commercial W-4wt% ThO2 cathode. The average vacuum arc-starting field intensity of the nanocomposite Mo-La2O3 cathode is 2.97×107 V/m, which is 62.7% lower than that of the commercial W-ThO2. The nanocomposite Mo-La2O3 cathode exhibits superior electron emission performances, and its distribution area and thickness of electron emission spots are remarkably larger, as compared to those of the commercial W-ThO2 cathode. The size of oxide particles has a great effect on the electron emission performances and vacuum arc characteristics of cathode. The electron emission performance of Mo-La2O3 cathode will be improved with decreasing of the lanthana particles size. When La2O3 particle size decreases to less than 100 nm, the electron emission area and ability of the Mo-La2O3 cathode significantly increase. The much enhanced electron emission performance of the nanocomposite Mo-La2O3 cathode is attributed to the formation of a higher inter electric field and space-charge regions at the interphase boundaries between Mo and La2O3 phases.

Study on Influence of Processes on the Dehydrogenation Performance of NaAlH4

Abstract In this paper, the effects of preparation process, ball-milling equipments, storing time and ball-milling time on the dehydrogenation performances were analyzed. All the samples were ball-milled by planetary ball mill except for sample 3 which was ball-milled by high-energy vibration ball mill. The results indicate that the above mentioned influence factors present obvious effect on the dehydrogenation performances of NaAlH 4 . The dehydrogenation amount of the samples turned up and down during ball milling increases by 50wt%. Compared to the samples prepared by planetary mill, the dehydrogenation amount of samples prepared by the high-energy vibration ball mill increases markedly. The results from studying on storing time and milling time show that the dehydrogenation amounts of the samples milled by planetary mill and laid aside for 24 h get an obvious increase. In addition, the amount of the hydrogen release of the samples milled for different time with planetary mill presents significantly difference. The amount of the hydrogen release of the sample milled for 80 min is higher than those milled for 100, 40 and 60 min. However, compared to other influence factors, the effect of ball-milling time on NaAlH 4 is smaller.

Effect of Ce4+ and Ce3+ on the Hydrogen Release of NaAlH4

Abstract The effects of CeCl 3 and Ce(SO 4 ) 2 doping on the hydrogen-release capacity of NaAlH 4 have been studied by pressure-composition-temperature equipment. The results show that the total amount and the rate of hydrogen release first increase and then decrease with increasing of CeCl 3 and Ce(SO 4 ) 2 contents. The rate and the amount of decomposition for the sample doped with 4 mol% CeCl 3 in the first-stage dehydrogenation processes are both better than those for the sample doped with 3 mol% Ce(SO 4 ) 2 . The rate and the amount of decomposition at 110, 130, 150 and 180 °C present an obvious increase with increasing of temperature.

Effect of LaCl3 and Ti on Hydrogen Storage Properties of NaAlH4 and LiAlH4

Abstract The effects of additives Ti and LaCl 3 on the hydrogen storage properties of NaAlH 4 and LiAlH 4 were investigated by the PCT (pressure-content-temperature) apparatus. NaAlH 4 doped with LaCl 3 and LiAlH 4 doped with LaCl 3 both show better capability of hydrogen release than the samples doped with Ti. The study on the first rehydrogenation cycle of NaAlH 4 doped with 3 mol% LaCl 3 finds that the dehydrogenation temperature has a marked decrease. In addition, the effect of LaCl 3 content on hydrogen release of NaAlH 4 is very obvious. The result indicates that the amount and rate of hydrogen release show the same change trends, increasing firstly and then decreasing with increasing of LaCl 3 content. The sample doped with 3 mol% LaCl 3 presents the best dehydrogenation properties in both the amount of hydrogen release and the desorption kinetics. The activation energy of the NaAlH 4 sample doped with 3 mol% LaCl 3 was measured to be 41.6 kJ/mol. This value is lower than that reported for the Ti-doped NaAlH 4 .

Effect of La3+ on Dehydrogenation Capacity of the LiAlH4− NH4Cl System

Abstract The effect of the catalysts LaCl 3 and La 2 O 3 on the dehydrogenation properties of the LiAlH 4 -NH 4 Cl system was analyzed. The results show that La 2 O 3 doping shortens the starting time of hydrogen release, and improves the rate of hydrogen release. While, LaCl 3 doping induces an obvious decrease of the rate of hydrogen release. Furthermore, the study shows that with the increase of the amounts of LaCl 3 and La 2 O 3 , the hydrogen release amounts of the samples present a gradual decrease within 180 min except for the sample doped with 3 mol% LaCl 3 . However, the maximum hydrogen release amount of the sample doped with La 2 O 3 is obviously higher than that of the sample doped with LaCl 3 . In addition, the analysis of the SEM images of the undoped sample and the doped samples indicates that the microstructure of all the samples seems to be similar and obvious differences are not found.

Effect of CeO2 and Y2O3 as Catalysts on Hydrogen Desorption Properties of NaAlH4

Abstract The effect of two rare earth oxides (0, 0.5, 1, 2, 3, 4, 5 mol% CeO 2 and 0, 0.5, 1, 2, 3, 4 mol% Y 2 O 3 ) on hydrogen desorption of NaAlH 4 by mechanical milling under an atmosphere of argon was studied. The PCT result reveals that increasing content of CeO 2 and Y 2 O 3 causes a similar effect trends on the maximum dehydrogenation amount and the dehydrogenation rate which increases firstly and then decreases under the same moderate conditions. CeO 2 as the catalyst for NaAlH 4 presents superior catalytic activity to Y 2 O 3 . For the same amount of 4.8 wt%, the dehydrogenation rate of that of 1 mol% CeO 2 -NaAlH 4 is obviously faster than that of 1 mol% Y 2 O 3 -NaAlH 4 . SEM analysis shows that with the increasing of catalyst content, the microscopic surface morphology of all the samples changes from homogeneous to flocculent. Besides, the dispersive particle structure may have a bigger reaction area than the flocculent structure and heating could make NaAlH 4 form a kind of porous structure like honeycomb.