催化剂对LiAlH4+MgH2体系放氢性能的影响及催化机理

采用机械球磨法在LiAlH4+MgH2体系中添加不同种类催化剂,以提高复合体系的放氢性能。运用XRD、SEM、EDS、XPS以及Sieverts法研究复合体系的结构以及放氢性能,并探讨TiF3的催化机理。结果表明:TiF3催化剂的添加显著降低了复合体系的起始放氢温度,提高了放氢动力学性能,该体系在84.1℃开始脱氢,放氢量(质量分数)达8.0%。热脱附过程中TiF3参与了反应,并生成含Tix+的未知化合物,有效地促进了LiAlH4和MgH2之间的协同放氢。复合体系掺杂TiF3后,其热脱附反应的活化能Ea为79.1 kJ/mol,与未添加TiF3的复合体系的活化能(91.3 kJ/mol)相比,TiF3的添加极大地降低了放氢反应动力学势垒。     

LiAlH4/2LiNH2复合体系的储氢性能

为了改善LiAlH4和LiNH2的储氢性能,将LiAlH4与LiNH2通过球磨制备成LiAlH4/2LiNH2复合储氢材料体系,采用X射线粉末衍射(XRD)仪、傅里叶红外光谱分析(FTIR)仪、同步热分析(TG/DSC)仪、核磁共振波谱分析(NMR)仪等测试手段研究LiAlH4/2LiNH2复合储氢材料的储氢性能以及放氢过程的结构变化,分析了LiAlH4与LiNH2相互作用的机制。结果表明:LiNH2的加入改变了LiAlH4的放氢反应路径,有效地降低了LiAlH4的分解放氢温度,其放氢过程主要进行两步反应,最终产物为Li3AlN2。     

Ce基催化剂对2LiBH4/MgH2放氢性能的影响

采用球磨方法制备了2LiBH4/MgH2复合储氢材料体系,用XRD、FTIR和储氢性能测试手段等对复合体系结构和储氢性能进行表征,研究了不同Ce基催化剂对复合体系放氢性能的影响,分析了催化剂的催化机理。结果表明:2LiBH4/MgH2复合物加热过程为明显的两步放氢,第1步主要发生MgH2的分解放氢;第2步为第1步生成的Mg与LiBH4发生放氢反应;添加Ce和CeF3都能提高2LiBH4/MgH2体系的放氢性能。Ce主要改善体系第2步放氢特性,CeF3对体系两步放氢反应均产生显著效果。添加5mol%CeF3使2LiBH4/MgH2体系起始放氢温度降低约100℃,体系最大放氢量达到10.6%(质量分数,下同);F-取代部分H-形成LiBH1-xFx,改善了LiBH4的分解特性,从而显著改善了2LiBH4/MgH2体系的放氢性能。     

不同催化剂对氢化铝锂(LiAlH4)可逆性能的影响

通过PCT(Pressure-Content-Temperature)设备研究了不同催化剂Ti、Ni、Fe、Ce(SO4)2 和 LaCl3对LiAlH4可逆储氢性能的影响.结果表明掺杂明显降低了试样的放氢速率,此外除了LaCl3,其他的掺杂还降低了试样的放氢温度,试样的放氢量也明显地下降了.掺杂1 mol% Ni, 1 mol% Ti, 1 mol% Ce(SO4)2 和 1 mol%LaCl3的LiAlH4可逆吸氢的研究发现,在180 ℃和 8 Mpa氢压的条件下,掺杂1 mol% Ni的试样表现出了最好的吸氢性能,其吸氢量达到了0.97%(质量分数).     

TiF3对氢化燃烧合成Mg95Ni5放氢性能的影响

研究了TiF3的添加对氢化燃烧合成Mg95Ni5放氢性能的影响。添加1%(摩尔分数,下同)TiF3机械球磨10h可使Mg95Ni5的放氢性能达到最佳,在523K时,1800s内的放氢量可达到5.20%(质量分数,下同),并使放氢反应的表观活化能从Mg95Ni5的124kJ/mol降低到86kJ/mol。研究表明,TiF3的催化作用可归因于生成的MgF2和Tix+的氢化物减弱了Mg-H鍵。     

LiBH4/Li3AlH6复合物的放氢性能与机理

采用机械球磨法制备LiBH4/Li3AlH6复合体系,通过TG/DSC/MS、XRD等方法对其储氢性能及机理进行研究,并对其放氢反应激活能进行计算。结果表明,LiBH4-Li3AlH6复合体系从室温加热到500℃条件下发生3步放氢反应:首先,Li3AlH6分解生成Al并放出氢;然后部分生成的Al与LiBH4发生反应放出氢气;最后,剩余的Al与LiH反应放出氢气。复合体系总的放氢量达到8.5%(质量分数,下同),完全放氢后的复合物在8MPa和400℃条件下最大吸氢量达到4.9%。并对LiBH4-Li3AlH6复合体系放氢过程机理进行了分析。     

LaCl3和Ti对氢化铝钠（NaAlH4）和氢化铝锂（LiAlH4）储氢性能的影响

通过PCT(pressure-content-temperature)设备研究催化剂Ti和 LaCl3对NaAlH4和LiAlH4储氢性能的影响.NaAlH4和LiAlH4掺杂LaCl3比掺杂Ti的放氢性能有明显提高.在吸氢性能的研究中发现,在第1个吸氢循环中,掺杂3 mol% LaCl3的NaAlH4试样的放氢温度明显降低.此外,LaCl3的摩尔含量对NaAlH4的放氢性能的影响是非常明显的.研究结果显示,随着LaCl3含量的增加,NaAlH4的放氢量和放氢速率显示出相同的变化趋势,即先增加后减少.其中掺杂3 mol% LaCl3的NaAlH4试样的放氢量最大并且放氢动力学性能最好,其激活能为41.6 kJ/mol,这个值低于所报道的掺杂Ti的NaAlH4的激活能.     

孔道Al2O3/SiO2对NaAlH4-Tm2O3体系储氢性能的影响

以机械球磨法制备具有可逆吸放氢性能的NaAlH4-Tm2O3储氢材料体系。利用相同制备方法进一步研究两种不同孔道材料(大孔Al2O3与介孔SiO2)对NaAlH4-Tm2O3体系储氢性能的影响,测试样品的循环吸放氢性能,并对样品吸放氢前后的结构进行表征。结果表明:大孔Al2O3材料的添加并不能明显改善NaAlH4-Tm2O3体系的放氢速率和放氢量,而介孔SiO2的加入使NaAlH4-Tm2O3体系在150℃条件下5 h内的首次放氢量(质量分数)达到4.61%,高于NaAlH4-Tm2O3体系的4.27%,增加了约8.0%。此外,添加介孔SiO2的NaAlH4-Tm2O3体系放氢速率也有所提高。     

La1．8Ca0．2Mg14Ni3＋x% Ti合金的微结构和储氢性能

研究了机械球磨La1.8Ca0.2Mg14Ni3＋x％Ti（质量分数，下同）（x=0，5，10）合金的微结构和储氢性能。气态吸放氢研究表明。加入钛粉球磨能有效提高合金的活化性能、储氢容量和吸放氢速率。铸态合金经过6次活化后，在613K时放氢量为4．12％（质量分数，下同）。加Ti球磨改性10h后，随着X增加，合金经过2次～3次循环基本完全活化。吸放氢性能也相应提高。Ti含量在x=0，5，10时合金在613K的放氢量分别为4．69％，4．80％，4．83％：当x=10时合金在373K的吸氢量达到3％以上，在600K经过2min就能达到4．81%（为最大吸氢量的97％）。微结构分析表明。具有表面催化活性的Ti粉与合金基体表面进行复合，并使合金发生部分非晶转变，能有效改善La1.8Ca0.2Mg14Ni3合金的储氢性能。     

掺杂稀土类催化剂对LiAlH4放氢性能和相结构的影响

采用球磨的方式在LiAlH4中分别掺入3种稀土催化剂LaCl3、CeCl3和Ce(SO4)2,研究了稀土催化剂对LiAlH4的相结构和放氢性能的影响。结果表明,在球磨过程中,掺杂Ce(SO4)2对LiAlH4的分解基本没有影响,而掺杂LaCl3和CeCl3则造成LiAlH4部分分解,产生了LiCl和Al3RE（RE=La,Ce）相。在LiAlH4放氢反应中,稀土催化剂的加入均使LiAlH4初始放氢温度降低,特别是Ce(SO4)2使第1步的放氢温度降低了约25 ℃。稀土催化剂有助于加快LiAlH4分解反应速率,提高LiAlH4的放氢性能。     

Hydrogen storage behaviors and microstructure of MF3 (M=Ti, Fe)-doped magnesium hydride

MgH2+10%MF3(M=Ti,Fe)(mass fraction) composites were prepared by ball-milling in hydrogen atmosphere,and their hydrogen storage behaviors and microstructure were investigated systematically.The results show that the hydriding and dehydriding kinetics of MgH2 are markedly improved by doping TiF3 and FeF3 fluorides.At 573 K,the two composites can absorb 5.67%-6.07%(mass fraction) hydrogen within 5 min under an initial hydrogen pressure of 3.5 MPa,and desorb 5.34%-6.02% hydrogen within 6 min.Furthermore,the composites can absorb hydrogen rapidly in moderate temperature range of 313-473 K.In comparison,TiF3-doped sample has a better hydriding-dehydriding kinetics than FeF3-doped sample.The microstructure analysis shows that some active particles including MgF2,TiH2 and Fe could be formed in the hydriding-dehydriding processes of the MF3-doped composites.From the Kissinger's plot,the apparent activation energies for the hydrogen desorption of the composites are estimated to be 74.1 kJ/mol for TiF3-doped composite and 77.6 kJ/mol for FeF3-doped composite,indicating MgH2 is significantly activated due to the catalytic effect of the doping of MF3.     

Effect of Ti content on the hydrogen storage properties of Zr_（1-x）Ti_xMn_2Ce_（0.015） alloys

The effect of Ti content on the hydrogen storage properties of Zr1-xTixMn2 Ce0.015(x = 0,0.2,0.3,0.5) alloys was studied by X-ray diffraction,scanning electron microscopy and pressure-composition(p-c) isotherm measurement.All of the alloys mainly consist of C14-type Laves and CeO2 phases.As the Ti content increases,the lattice parameters of the Laves phase decrease and the unit cell shrinks anisotropically,the total hydrogen absorption capacity decreases but the reversible hydrogen desorption capacity of the alloys increases,and the equilibrium pressure of the alloys increases but the plateau becomes sloping.The changes of hydrogen storage properties of Zr1-xTixMn2 Ce0.015 alloys are related to the differences in both atomic radius and hydrogen affinity between Ti and Zr elements.     

Reversible hydrogen storage properties of NaAlH4 catalyzed with scandium

A systematic study was carried out to compare the reversible hydrogen storage properties of Sc-doped NaAlH₄ with Ti-doped NaAlH₄. Uncycled and cycled (five times) samples of 1, 2 and 4 mol% Sc-doped NaAlH₄ and 4 mol% Ti-doped NaAlH₄ were examined. Temperature programmed desorption, constant temperature desorption, and constant temperature cycling results revealed the following: Sc-doped NaAlH₄ realized very fast hydrogenation kinetics, reasonably fast dehydrogenation kinetics and minimal hydrogen capacity losses during cycling over a broad range of temperatures without any additives or co-dopants. Sc-doped NaAlH₄ also exhibited comparable kinetics and a higher hydrogen storage capacity compared to Ti-doped NaAlH₄, depending on the temperature, metal dopant level, and cycling. Sc exhibited this superior performance over Ti perhaps because Sc is an earlier transition metal than Ti.     

Effect of Ti content on the hydrogen storage properties of Zr1-xTixMn2Ce0.015 alloys

The effect of Ti content on the hydrogen storage properties of Zr1-xTixMn2 Ce0.015 (x = 0,0.2,0.3,0.5) alloys was studied by X-ray diffraction, scanning electron microscopy and pressure-composition (p-c) isotherm measurement. All of the alloys mainly consist of C14-type Laves and CeO2 phases. As the Ti content increases, the lattice parameters of the Laves phase decrease and the unit cell shrinks anisotropically, the total hydrogen absorption capacity decreases but the reversible hydrogen desorption capacity of the alloys increases, and the equilibrium pressure of the alloys increases but the plateau becomes sloping. The changes of hydrogen storage properties of Zr1-xTixMn2 Ce0.015 alloys are related to the differences in both atomic radius and hydrogen affinity between Ti and Zr elements.