共查询到20条相似文献,搜索用时 31 毫秒
1.
Renjin Xiong Ge SangXiayan Yan Guanghui ZhangXiaoqiu Ye Xinliang Zhu 《International Journal of Hydrogen Energy》2011,36(24):15652-15657
Nanocrystalline titanium dioxide/carbon composite (TiO2/C) was synthesized through a direct solution-phase carburization using tetrabutyl titanate (Ti(OBu)4) and resol as precursors. The prepared TiO2/C composite was mainly in the anatase structure with an average particle size under 20 nm, which was then introduced in NaAlH4 as a catalyst through ball milling. The desorption curves show that both nanocrystalline TiO2/C and TiO2 can obviously improve the kinetics of NaAlH4, while NaAlH4 with 3 mol% TiO2/C exhibits better cycling stability than NaAlH4 with 3 mol%TiO2. The hydrogen storage capacity of NaAlH4 with TiO2/C remains stable after 5th cycle, and about 94% of initial hydrogen is released, while the capacity of NaAlH4 with TiO2 decreases continuously during cycling, and only 88% of initial hydrogen is released after 10th cycle. Furthermore, NaAlH4 with 3 mol%TiO2/C exhibits good reversibility at relatively low hydrogen pressures, and it can reload 4.16 and 1.63wt% hydrogen at 50 and 30 bar hydrogen pressures, respectively. 相似文献
2.
Yaping Wang Qiuli RenYijing Wang Li LiDawei Song Lifang JiaoHuatang Yuan 《International Journal of Hydrogen Energy》2010
Co–B doped NaAlH4 is successfully synthesized by two-step synthesis process. The first activation step is milling NaH/Al powder and Co–B mixtures under Ar atmosphere. The second step is milling in a lower hydrogen pressure atmosphere. XRD patterns and FTIR spectrum demonstrate that NaAlH4 is completely formed after 15 h milling in Ar atmosphere following by 40 h milling in 2 MPa H2 atmosphere. PCT curves of as-prepared NaAlH4 show that it can release hydrogen at a low temperature of 90 °C. The activation energy value calculated by Arrhenius equation is only 67.95 kJ mol−1. Moreover, the formation mechanism of NaAlH4 is also discussed. 相似文献
3.
Yindee Suttisawat Visara Jannatisin Pramoch Rangsunvigit Boonyarach Kitiyanan Nongnuj Muangsin Santi Kulprathipanja 《Journal of power sources》2007
The main objective of this work was to investigate the different effects of transition metals (TiO2, VCl3, HfCl4) on the hydrogen desorption/absorption of NaAlH4. The HfCl4 doped NaAlH4 showed the lowest temperature of the first desorption at 85 °C, while the one doped with VCl3 or TiO2 desorbed at 135 °C and 155 °C, respectively. Interestingly, the temperature of desorption in subsequent cycles of the NaAlH4 doped with TiO2 reduced to 140 °C. On the contrary, in the case of NaAlH4 doped with HfCl4 or VCl3, the temperature of desorption increased to 150 °C and 175 °C, respectively. This may be because Ti can disperse in NaAlH4 better than Hf and V; therefore, this affected segregation of the sample after the desorption. The maximum hydrogen absorption capacity can be restored up to 3.5 wt% by doping with TiO2, while the amount of restored hydrogen was lower for HfCl4 and VCl3 doped samples. XRD analysis demonstrated that no Ti-compound was observed for the TiO2 doped samples. In contrast, there was evidence of Al–V alloy in the VCl3 doped sample and Al–Hf alloy in the HfCl4 doped sample after subsequent desorption/absorption. As a result, the V- or Hf-doped NaAlH4 showed the lower ability to reabsorb hydrogen and required higher temperature in the subsequent desorptions. 相似文献
4.
M. Sterlin Leo Hudson Himanshu RaghubanshiD. Pukazhselvan O.N. Srivastava 《International Journal of Hydrogen Energy》2012
The present paper reports the catalytic effect of carbon nanomaterials, particularly carbon nanotubes (CNTs) and graphitic nanofibres (GNFs) with two different structure morphology, namely planar GNFs (PGNFs) and helical GNFs (HGNFs) as the catalyst for improving the dehydrogenation and rehydrogenation behavior of sodium aluminum hydride (NaAlH4). It has been observed that HGNFs posses superior catalytic activity than other carbon nanoforms in improving the desorption kinetics and decreasing the desorption temperature of NaAlH4. Temperature programmed desorption (TPD) reveals that HGNFs admixed NaAlH4 undergo hydrogen desorption at a much lower temperature than PGNFs and CNTs (SWCNTs and MWCNTs) admixed NaAlH4. Thus for the heating rate of 2 °C/min, the peak desorption temperature corresponds to initial step decomposition of NaAlH4 admixed with 2 wt.% HGNFs and 2 wt.% PGNFs has been lowered to 143.6 °C and 152.6 °C, respectively (for pristine NaAlH4, it is ∼170 °C). In addition to the enhancement in desorption kinetics, the HGNFs admixed NaAlH4 undergoes fast rehydrogenation at the moderate condition. Microstructural investigation reveals that the HGNFs were present on the surface of NaAlH4 grains, whereas CNTs were tunneled into the grains of NaAlH4 suggesting a distinct catalytic behavior of different carbon nanovariants. 相似文献
5.
Jun MaJie Li Renying TangDongwei Li Wenzhang LiQiyuan Chen 《International Journal of Hydrogen Energy》2011,36(15):9091-9097
The co-effects of lanthanide oxide Tm2O3 and porous silica on the hydrogen storage properties of sodium alanate are investigated. NaAlH4-Tm2O3 (10 wt%) and NaAlH4-Tm2O3 (10 wt%)-porous SiO2 (10 wt%) are prepared by the ball milling method, and their hydrogen desorption/re-absorption capacities are compared. Dehydrogenation process was performed at 150 °C under vacuum and rehydrogenation was performed at 150 °C for 4 h under ∼9 MPa in highly pure hydrogen. The results show that Tm2O3 has a catalytic effect on the hydrogen desorption and re-absorption of NaAlH4. The hydrogen desorption capacity of Tm2O3 single-doped NaAlH4 is 4.6 wt%, higher than that of undoped NaAlH4 (4.3 wt%). During the dehydrogenation process, NaAlH4 is completely decomposed and no intermediate product Na3AlH6 is detected. The addition of porous silica improves the dehydrogenation performance of NaAlH4. Tm2O3 and porous silica co-doped NaAlH4 could release a maximum hydrogen amount of 4.7 wt%, higher than that of undoped NaAlH4 and Tm2O3 single-doped NaAlH4. Moreover, porous silica improves the reversibility of hydrogen storage in NaAlH4. 相似文献
6.
Jianfeng Mao Zaiping Guo Huakun Liu 《International Journal of Hydrogen Energy》2011,36(22):14503-14511
The effect of NbF5 on the hydrogen sorption performance of NaAlH4 has been investigated. It was found that the dehydrogenation/hydrogenation properties of NaAlH4 were significantly enhanced by mechanically milling with 3 mol% NbF5. Differential scanning calorimetry results indicate that the ball-milled NaAlH4-0.03NbF5 sample lowered the completion temperature for the first two steps dehydrogenation by 71 °C compared to the pristine NaAlH4 sample. Isothermal hydrogen sorption measurements also revealed a significant enhancement in terms of the sorption rate and capacity, in particular, at reduced operation temperatures. The apparent activation energy for the first-step and the second-step dehydrogenation of the NaAlH4-0.03NbF5 sample is estimated to be 88.2 kJ/mol and 102.9 kJ/mol, respectively, by using Kissinger’s approach, which is much lower than for pristine NaAlH4, indicating the reduced kinetic barrier. The rehydrogenation kinetics of NaAlH4 was also improved with 3 mol% NbF5 doping, absorbing ∼1.7 wt% hydrogen at 150 °C for 2 h under ∼5.5 MPa hydrogen pressure. In contrast, no hydrogen was absorbed by the pristine NaAlH4 sample under the same conditions. The formation of Na3AlH6 was detected by X-ray diffraction on the rehydrogenated NaAlH4-0.03NbF5 sample. Furthermore, the structural changes in the NbF5-doped NaAlH4 sample after ball milling and the hydrogen sorption were carefully examined, and the active species and mechanism of catalysis in NbF5-doped NaAlH4 are discussed. 相似文献
7.
Himanshu Raghubanshi M. Sterlin Leo HudsonO.N. Srivastava 《International Journal of Hydrogen Energy》2011,36(7):4482-4490
In this communication, we report the synthesis of helical carbon nanofibres (HCNFs) by employing hydrogen storage intermetallic LaNi5 as the catalyst precursor. It was observed that oxidative dissociation of LaNi5 alloy (2LaNi5 + 3/2O2 → La2O3 + 10Ni) occurred during synthesis. The Ni particles obtained through this process instantly interacted with C2H2 and H2 gases, and fragmented to nanoparticles of Ni (∼150 nm) with polygonal shape. These polygonal shapes of Ni nanoparticles were decisive for the growth of helical carbon nanofibres (HCNFs) at 650 °C. TEM, SAED and EDAX studies have shown that HCNFs have grown on Ni nanoparticles. Typical diameter and length of the HCNFs are ∼150 nm and 6-8 μm respectively. BET surface area of these typical HCNFs has been found to be 127 m2/g. It was found that at temperature 750 °C, spherical shapes of Ni nanoparticles were produced and decisive for the growth of planar carbon nanofibres (PCNFs). The diameter and length of the PCNFs are ∼200 nm and 6-8 μm respectively. In order to explore the application potential of the present as-synthesized CNFs, they were used as a catalyst for enhancing the hydrogen desorption kinetics of sodium aluminum hydride (NaAlH4). We have found that the present as-synthesized HCNFs, with metallic impurities, indeed work as an effective catalyst. The pristine NaAlH4 and 8 mol% as-synthesized HCNFs admixed NaAlH4, at 160 °C-180 °C and for the duration of 5 h, liberate 0.8 wt% and 4.36 wt% of hydrogen, respectively. Thus there is an enhancement of ∼5 times in kinetics when as-synthesized HCNFs are used as the catalyst. To the best of our knowledge, the use of hydrogen storage alloy LaNi5 as the catalyst precursor for the growth of HCNFs has not yet been done and thus represents a new feature relating to the growth of HCNFs. Furthermore, we have shown that the as-synthesized HCNFs work as an effective new catalyst for improving the dehydrogenation kinetics of the complex hydride, NaAlH4. 相似文献
8.
Gil-Jae Lee Jae-Hyeok Shim Young Whan Cho Kyung Sub Lee 《International Journal of Hydrogen Energy》2008
NaAlH4 has been homogeneously mixed with micron- and nano-sized TiO2 powders by high-energy ball milling and their sorption properties have been investigated during hydrogen absorption/desorption cycles. NaAlH4 with TiO2 nanopowder exhibits as good desorption kinetics as NaAlH4 with TiCl3, whereas poor desorption kinetics is observed with micron-sized TiO2 powder. NaAlH4 with TiO2 nanopowder also provides improved cyclic property compared to NaAlH4 with TiCl3 in terms of both desorption rate and hydrogen capacity. X-ray diffraction analysis shows that micron-sized TiO2 remains stable with NaAlH4 after milling, although thermodynamic calculation predicts that TiO2 reacts with NaAlH4. 相似文献
9.
Ashish Bhatnagar Sunita K. Pandey Viney Dixit Vivek Shukla Rohit R. Shahi M.A. Shaz O.N. Srivastava 《International Journal of Hydrogen Energy》2014
The present investigation describes the hydrogen storage properties of 2:1 molar ratio of MgH2–NaAlH4 composite. De/rehydrogenation study reveals that MgH2–NaAlH4 composite offers beneficial hydrogen storage characteristics as compared to pristine NaAlH4 and MgH2. To investigate the effect of carbon nanostructures (CNS) on the de/rehydrogenation behavior of MgH2–NaAlH4 composite, we have employed 2 wt.% CNS namely, single wall carbon nanotubes (SWCNT) and graphene nano sheets (GNS). It is found that the hydrogen storage behavior of composite gets improved by the addition of 2 wt.% CNS. In particular, catalytic effect of GNS + SWCNT improves the hydrogen storage behavior and cyclability of the composite. De/rehydrogenation experiments performed up to six cycles show loss of 1.50 wt.% and 0.84 wt.% hydrogen capacity in MgH2–NaAlH4 catalyzed with 2 wt.% SWCNT and 2 wt.% GNS respectively. On the other hand, the loss of hydrogen capacity after six rehydrogenation cycles in GNS + SWCNT (1.5 + 0.5) wt.% catalyzed MgH2–NaAlH4 is diminished to 0.45 wt.%. 相似文献
10.
M. Ismail Y. Zhao X.B. Yu I.P. NevirkovetsS.X. Dou 《International Journal of Hydrogen Energy》2011,36(14):8327-8334
The effects of TiO2 nanopowder addition on the dehydrogenation behaviour of LiAlH4 have been studied. The 5 wt.% TiO2-added LiAlH4 sample showed a significant improvement in dehydrogenation rate compared to that of undoped LiAlH4, with the dehydrogenation temperature reduced from 150 °C to 60 °C. Kinetic desorption results show that the added LiAlH4 released about 5.2 wt% hydrogen within 30 min at 100 °C, while the as-received LiAlH4 just released below 0.2 wt.% hydrogen within same time at 120 °C. From the Arrhenius plot of the hydrogen desorption kinetics, the apparent activation energy is 114 kJ/mol for pure LiAlH4 and 49 kJ/mol for the 5 wt.% TiO2 added LiAlH4, indicating that TiO2 nanopowder adding significantly decreased the activation energy for hydrogen desorption of LiAlH4. X-ray diffraction and Fourier transform infrared analysis show that there is no phase change in the cell volume or on the Al-H bonds of the LiAlH4 due to admixture of TiO2 after milling. X-ray photoelectron spectroscopy results show no changes in the Ti 2p spectra for TiO2 after milling and after dehydrogenation. The improved dehydrogenation behaviour of LiAlH4 in the presence of TiO2 is believed to be due to the high defect density introduced at the surfaces of the TiO2 particles during the milling process. 相似文献
11.
In a previous paper, it was demonstrated that a MgH2–NaAlH4 composite system had improved dehydrogenation performance compared with as-milled pure NaAlH4 and pure MgH2 alone. The purpose of the present study was to investigate the hydrogen storage properties of the MgH2–NaAlH4 composite in the presence of TiF3. 10 wt.% TiF3 was added to the MgH2–NaAlH4 mixture, and its catalytic effects were investigated. The reaction mechanism and the hydrogen storage properties were studied by X-ray diffraction, thermogravimetric analysis, differential scanning calorimetry (DSC), temperature-programmed-desorption and isothermal sorption measurements. The DSC results show that MgH2–NaAlH4 composite milled with 10 wt.% TiF3 had lower dehydrogenation temperatures, by 100, 73, 30, and 25 °C, respectively, for each step in the four-step dehydrogenation process compared to the neat MgH2–NaAlH4 composite. Kinetic desorption results show that the MgH2–NaAlH4–TiF3 composite released about 2.4 wt.% hydrogen within 10 min at 300 °C, while the neat MgH2–NaAlH4 sample only released less than 1.0 wt.% hydrogen under the same conditions. From the Kissinger plot, the apparent activation energy, EA, for the decomposition of MgH2, NaMgH3, and NaH in the MgH2–NaAlH4–TiF3 composite was reduced to 71, 104, and 124 kJ/mol, respectively, compared with 148, 142, and 138 kJ/mol in the neat MgH2–NaAlH4 composite. The high catalytic activity of TiF3 is associated with in situ formation of a microcrystalline intermetallic Ti–Al phase from TiF3 and NaAlH4 during ball milling or the dehydrogenation process. Once formed, the Ti–Al phase acts as a real catalyst in the MgH2–NaAlH4–TiF3 composite system. 相似文献
12.
Xuezhang XiaoKairong Yu Xiulin FanZhe Wu Xinhua WangChangpin Chen Qidong WangLixin Chen 《International Journal of Hydrogen Energy》2011,36(1):539-548
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. 相似文献
13.
Jinbao Gao Peter Ngene Monika Herrich Wei Xia Oliver Gutfleisch Martin Muhler Krijn P. de Jong Petra E. de Jongh 《International Journal of Hydrogen Energy》2014
For practical solid-state hydrogen storage, reversibility under mild conditions is crucial. Complex metal hydrides such as NaAlH4 and LiBH4 have attractive hydrogen contents. However, hydrogen release and especially uptake after desorption are sluggish and require high temperatures and pressures. Kinetics can be greatly enhanced by nanostructuring, for instance by confining metal hydrides in a porous carbon scaffold. We present for a detailed study of the impact of the nature of the carbon–metal hydride interface on the hydrogen storage properties. Nanostructures were prepared by melt infiltration of either NaAlH4 or LiBH4 into a carbon scaffold, of which the surface had been modified, varying from H-terminated to oxidized (up to 4.4 O/nm2). It has been suggested that the chemical and electronic properties of the carbon/metal hydride interface can have a large influence on hydrogen storage properties. However, no significant impact on the first H2 release temperatures was found. In contrast, the surface properties of the carbon played a major role in determining the reversible hydrogen storage capacity. Only a part of the oxygen-containing groups reacted with hydrides during melt infiltration, but further reaction during cycling led to significant losses, with reversible hydrogen storage capacity loss up to 40% for surface oxidized carbon. However, if the carbon surface had been hydrogen terminated, ∼6 wt% with respect to the NaAlH4 weight was released in the second cycle, corresponding to 95% reversibility. This clearly shows that control over the nature and amount of surface groups offers a strategy to achieve fully reversible hydrogen storage in complex metal hydride-carbon nanocomposites. 相似文献
14.
Lijing Guo Lifang JiaoLi Li Qinghong WangGuang Liu Hongmei DuQiong Wu Juan DuJiaqin Yang Chao YanYijing Wang Huatang Yuan 《International Journal of Hydrogen Energy》2013
LiBH4 nano-particles are incorporated into mesoporous TiO2 scaffolds via a chemical impregnation method. And the enhanced desorption properties of the composite have been investigated. The LiBH4/TiO2 sample starts to release hydrogen at 220 °C and the maximal desorption peak occurs at about 330 °C, much lower compared to the bulk LiBH4. Furthermore, the composite exhibits excellent dehydrogenation kinetics, with 11 wt% of hydrogen liberated from LiBH4 at 300 °C within 3 h. X-ray diffraction and Fourier transform infrared spectroscopy are used to confirm the nanostructure of LiBH4 in the TiO2 scaffold. This work demonstrates that confinement within active porous scaffold host is a promising approach for enhancing hydrogen decomposition properties of light-metal complex hydrides. 相似文献
15.
This study reports the synthesis of NaAlH4 by ball milling of NaH and Al mixture along with 3 mol % Mischmetal (Mm) nanocatalyst under hydrogen atmosphere. It is observed that synthesis of the intermediate phase Na3AlH6 can be achieved by ball milling even under 1 atm hydrogen at room temperature. Ball milling of the NaH + Al with 3 mol % Mm with 3 atm hydrogen in excess of 40 h time did not lead to the formation of NaAlH4 but charging of the milled material at 100 atm hydrogen pressure at 120 °C lead to formation of NaAlH4 phase. Direct synthesis of NaAlH4 was achieved by milling of NaH + Al with 3 mol % Mm under 100 atm hydrogen pressure. Direct synthesis is possible even without any catalyst by high pressure milling. However catalyst is required to improve the hydrogen sorption characteristics of the synthesized material. The as-prepared Mm catalyzed NaAlH4 is also found to reversibly store hydrogen up to 4.2 wt% hydrogen. Catalytic activity is attributed to defects promoted by ball milling and catalysts. 相似文献
16.
Dehydrogenation of NaAlH4 can be greatly facilitated by activated carbon catalysts. The catalytic function can be further enhanced by decorating the carbon with Co, Ni, or Cu nanoparticles. The decomposition temperature was lowered by as much as 100 °C using a 3 wt.% Co or Ni-decorated activated carbon, comparable to a Ti-based catalyst, which were the most effective among the metals tested. The catalytic effect is likely due to a combination of hydrogen spillover effect, high contact area between carbon and the hydride, and confinement of the hydride as nano-sized domains in the pores of the carbon matrix. The catalysts were also effective in facilitating rehydrogenation of NaAlH4 under moderate pressure (75.8 bar H2) and low temperature (120 °C), when no rehydrogenation would occur without the catalyst. The fact that this new catalyst system is not specific to any hydride offers many potential applications. 相似文献
17.
Hao-Yuan Zheng Zhi-Qiang Ding Yan-Jun Xie Jun-Feng Li Cun-Ke Huang Wei-Tong Cai Hai-Zhen Liu Jin Guo 《International Journal of Hydrogen Energy》2021,46(5):4168-4180
In this study, NaAlH4?based hydrogen storage materials with dopants were prepared by a two-steps in-situ ball milling method. The dopants adopted included Ce, few layer graphene (FLG), Ce + FLG, and CeH2.51. The hydrogen storage materials were studied by non-isothermal and isothermal hydrogen desorption measurements, X-ray diffractions analysis, cycling sorption tests, and morphology analysis. The hydrogen storage performance of the as-prepared NaAlH4 with Ce addition is much better than that with CeH2.51 addition. This is due to that the impact of Ce occurs from the body to the surface of the materials. The addition of FLG further enhances the impact of Ce on the hydrogen storage performance of the materials. The hydrogen storage capacity, hydrogen sorption kinetics, and cycle performance of NaAlH4 with Ce + FLG additions are all better than NaAlH4 materials with the addition of either Ce or FLG alone. The NaAlH4 with Ce and FLG addition starts to release hydrogen at 85 °C and achieves a capacity of 5.06 wt% after heated to 200 °C. The capacity maintains at 4.91 wt% (94.7% of the theoretical value) for up to 8 cycles. At 110 °C, the material can release isothermally a hydrogen capacity of 2.8 wt% within 2 h. The activation energies for the two hydrogen desorption steps of NaAlH4 with Ce and FLG addition are estimated to be 106.99 and 125.91 kJ mol?1 H2, respectively. The related mechanisms were studied with first-principle and experimental methods. 相似文献
18.
Li Li Fangyuan QiuYijing Wang Yanan XuCuihua An Guang LiuLifang Jiao Huatang Yuan 《International Journal of Hydrogen Energy》2013
The hydrogen storage properties of LiAlH4 doped efficient TiN catalyst were systematically investigated. We observe that TiN catalyst enhances the dehydrogenation kinetics and decreases the dehydrogenation temperature of LiAlH4. The dehydrogenation behaviors of 2%TiN–LiAlH4 are investigated using temperature programmed desorption (TPD), differential scanning calorimetry (DSC) and fourier transform infrared spectroscopy (FTIR). Interestingly, the onset hydrogen desorption temperature of 2%TiN–LiAlH4 sample gets lowered from 151.0 °C to 90.0 °C with a faster kinetics, and the dehydrogenation rate reached a maximum value at 137.2 °C. By adding a small amount of as-prepared TiN, approximately 7.1 wt% of hydrogen can be released from the LiAlH4 at 130 °C. Interestingly, the result of the FTIR indicates that the 2%TiN–LiAlH4 maybe restore hydrogen under 5.5 MPa hydrogen. Moreover, 2%TiN–LiAlH4 displayed a substantially reduced activation energy for LiAlH4 dehydrogenation. 相似文献
19.
M.P. Pitt P.E. Vullum M.H. Sørby H. Emerich M. Paskevicius C.J. Webb E.MacA. Gray C.E. Buckley J.C. Walmsley R. Holmestad B.C. Hauback 《International Journal of Hydrogen Energy》2012
The hydrogen cycled (H) planetary milled (PM) NaAlH4 + xM (x < 0.1) system (M = 30 nm Ag, 80 nm Al, 2–3 nm C, 30 nm Cr, 25 nm Fe, 30 nm Ni, 25 nm Pd, 65 nm Ti) has been studied by high resolution synchrotron powder X-ray diffraction. Isothermal absorption kinetic isotherms have been measured over the first two H cycles. The PM NaAlH4 + 0.1Ti system has also been studied by high resolution transmission electron microscopy (TEM). 80 nm Al and 2–3 nm C were inactive, and would not allow hydrogen (H) desorption from NaAlH4. 30 nm Cr, 25 nm Fe, 30 nm Ni, and 25 nm Pd showed activity, but with weak kinetics of only ca. 1 wt.% H/hour. The NaAlH4 + 0.1Ti system displays absorption kinetics of ca. 7 wt.% H/hour, comparable to TiCl3 enhanced NaAlH4 after five H cycles. After H cycling the PM NaAlH4 + 0.1Ti system, we observe a body centred tetragonal (bct) χ-TiH2 phase, which displays intense anisotropic peak broadening. The broadening is evident as a massive dislocation density of ca. 1.20 × 1017/m2 in high resolution TEM images of the χ-TiH2 phase. All originally added Ti can be accounted for in the bct χ-TiH2 phase by quantitative phase analysis (QPA) after five H cycles. The PM NaH + Al + 0.02 (Ti-nano-alloy) system shows absorption kinetic rates in the order TiO2 > TiN > TiC > Ti, with rapid hydrogenation kinetics of ca. 23 wt.% H/hour for TiO2 enhanced NaAlH4, equivalent to TiCl3 enhanced NaAlH4. The TiN and TiC are partially reduced by ca. 7 and 22% respectively, and the TiO2 is completely reduced. The location of the reduced Ti cannot be discerned by X-ray diffraction at these minor proportions. 相似文献
20.
A. Esfandiar S. Ghasemi A. Irajizad O. Akhavan M.R. Gholami 《International Journal of Hydrogen Energy》2012
Reduced graphene oxide (RGO) was used to improve the hydrogen sensing properties of Pd and Pt-decorated TiO2 nanoparticles by facile production routes. The TiO2 nanoparticles were synthesized by sol–gel method and coupled on GO sheets via a photoreduction process. The Pd or Pt nanoparticles were decorated on the TiO2/RGO hybrid structures by chemical reduction. X-ray photoelectron spectroscopy demonstrated that GO reduction is done by the TiO2 nanoparticles and Ti–C bonds are formed between the TiO2 and the RGO sheets as well. Gas sensing was studied with different concentrations of hydrogen ranging from 100 to 10,000 ppm at various temperatures. High sensitivity (92%) and fast response time (less than 20 s) at 500 ppm of hydrogen were observed for the sample with low concentration of Pd (2 wt.%) decorated on the TiO2/RGO sample at a relatively low temperature (180 °C). The RGO sheets, by playing scaffold role in these hybrid structures, provide new pathways for gas diffusion and preferential channels for electrical current. Based on the proposed mechanisms, Pd/TiO2/RGO sample indicated better sensing performance compared to the Pt/TiO2/RGO. Greater rate of spill-over effect and dissociation of hydrogen molecules on Pd are considered as possible causes of the enhanced sensitivity in Pd/TiO2/RGO. 相似文献