镧镍铜钴储氢合金的制备与性质

以LaNi₅为代表的镧系储氢合金有优良的吸放氢性能,抗中毒能力强,因而受到广泛重视^[1]. 目前已开发出许多二元及多元镧系合金,并研究了部分合金的表面性质^[1～4],但结果并不一致. 本文制备了四元合金LaNi₄Cu_0.5Co_0.5,通过X 射线光电子能谱(XPS)、扫描电镜(SEM)和吸氢测试等方法研究该合金的性质。     

我国金属氢化物化学研究

综述了我国金属氢化物化学的发展。我国是从５０年代中期开始研究离子型金属氢化物的合成、性能和应用的,发展了一些合成方法,获得了多项中国专利。储氢合金的化学研究是７０年代中期开始的。在储氢合金的化学合成、吸放氢热力学与动力学、储氢合金氢化催化和电化学方面都有较深入的研究,特别是储氢电极合金电化学及其在Ｎｉ／ＭＨ可逆电池中的应用研究,在国家８６３计划强有力的支持下,某些方面进入了国际先进行列。     

稀土储氢合金浆液的吸氢性能

研究了富镧混合稀土－镍储氢合金与有机溶剂组成的悬浮浆液的吸氢行为。测定了温度,搅拌速度及浆液中合金含量对吸氢速率的影响,并以膜模型进行分析,计算。在温度４０℃和４２ｒ．ｓ＾－１的搅拌速度下,合金含量为０．０８ｋｇ．ｋｇ＾－１的浆液中,金属氢化物的转化率可达９５％。     

多壁碳纳米管储氢的物理吸附特性

The physisorption of hydrogen stored in armchair multi-walled carbon nanotubes (MWCNTs) is simulated by the grand canonical Monte Carlo (GCMC) method on the condition of 10 MPa at normalt emperature. Hydrogen-hydrogen and hydrogen-carbon interactions are both modeled with Lennard-Jones potential. The hydrogen storage in double-walled carbon-nanotubes (DWCNTs) has been investigated on the condition that the internal or external radius is changed while the other radius remains constant. The results show that hydrogen molecules are mostly absorbed near the tube walls, and the hydrogens to rage capacityisim proved effectively when the difference between the internal radius and the external radius increases from 0.34 to 0.61 or 0.88 nm. Its simple theoretic explanation also is given. Further more, the capacity of hydrogen physisorbed in there-walled carbon nanotubes (TWCNTs) is calculated when the wall-wall distance is 0.34, 0.61 and 0.88 nm respectively. Then its hydrogen storage capacity is compared with that of single-walled carbon nanotubes (SWCNTs) and DWCNTs, and it is discovered that the capacity of hydrogen physisorbed in MWCNTs decreases as the number of wall increases.     

MLi2H3(M=Na,K)与NH3反应的密度泛函理论研究

采用杂化密度泛函方法,对MLi₂H₃(M=Na, K)团簇与NH₃的反应机理进行计算分析,对反应中各驻点几何构型进行优化,经频率分析和内禀反应坐标计算以确证各驻点的正确性和连接关系.经单点能校正计算,给出反应相关的能量信息.结果表明：引入Na和K原子后,反应物LOMO轨道有大幅度的向Na、K原子处的转移. KLi₂H₃有较小的能隙和电离势及较高的费米能,有较高反应活性. Na、K元素的引入,能破坏反应物的稳定性,降低反应能垒.     

嵌入配位不饱和金属位对多孔芳香骨架材料储氢性能的影响

基于密度泛函理论(DFT)和巨正则蒙特卡洛(GCMC)模拟方法,系统地研究了引入配位不饱和金属位(CUS)对PAF-30n (n = 1–4)材料储氢性能影响的规律。结果表明,77 K下PAF-302MgO₂_PBE100的最大过量质量储氢量达到7.97% (w);77 K、10 MPa下100%醇镁功能化改性PAF-302和PAF-303的绝对储氢量分别达到9.9% (w) (65.9 g∙L^-1)和15.0% (w) (50.5 g∙L^-1),分别超过美国能源部(DOE)标准80% (64.8%)和173% (26.3%),均超过在相同条件下目前储氢性能最佳的NU-1101 (9.1% (w), 46.6 g∙L^-1)。即使在243 K、10 MPa下,其绝对质量和绝对体积储氢量也能分别达到5.13% (w)和34.19 g∙L^-1,占DOE质量与体积储氢标准的93.3%和85.5%,是目前为止常温储氢性能较为均衡的多孔材料之一。结合等量吸附热(Q_st)、径向分布函数(RDF)和质心几率密度分布(MCPD)方法进一步分析,发现有机链长度增加导致孔隙率增加和体积比表面积减小,是引起多孔材料绝对质量和绝对体积储氢量此消彼长的根本原因。另外,引入CUS能提高PAFs材料对H₂分子亲和力,显著增强其体积储氢量。     

铈添加对Ti16.5Cr20(V45Fe8.5)0.98Si2合金结构及储氢性能的影响

通过XRD,SEM,恒温等容储氢性能测试等方法,研究了Ce添加对Ti26.5Cr20(V45Fe8.5)0.98Si2Cex(x=0～2.0%(原子分数))合金结构及储氢性能的影响.结果表明,Ti16.5Cr20如(V45Fe8.5)0.98 Si2Cex(x=0～2.0%)合金为BCC和C14 Laves相双相合金,随合金中Ce添加量的增加,合金的晶格常数增大,而合金中C14 Laves相的含量减少.平衡压从0.233 MPa降低到0.167 MPa,合金的吸氢动力学性能得到改善,最大吸氢量也由3.08%增加至3.19%(质量分数),PCT曲线的平台斜率减小.合金的储氢性能的改善与Ce的加入抑制了部分C14 Laves相的析出,减少了合金中C14 Laves相的含量密切相关.     

La0.7-xNdxMg0.3Ni3.4Al0.1(x=0～0.4)储氢合金的相结构及电化学性能

采用真空烧结方式制备了AB3.5型La0.7-xNdxMg0.3Ni3.4Al0.1(x=0,0.1,0.2,0.3和0.4)储氢合金.XRD分析表明,所有合金均由LaNi5,La2Ni7和LaNi3三相组成.当Nd含量增加时,合金中的LaNi5和La2Ni7相含量有不同程度的增加,而LaNi3相相应减少.电化学性能测试表明,添加适量的Nd能改善合金电极的循环稳定性,其中La0.6Nd0.1Mg0.3Ni3.4Al0.1合金具有相对较好的综合性能,其最大放电容量达到322.4 mAh·g-1,循环50周的容量保持率(S50)达到89.98%.     

V2.1TiNi0.4Zr0.06Cu0.03M0.10 (M=Cr,Co, Fe,Nb, Ta)储氢合金的微结构及电化学性能

采用磁悬浮感应熔炼方法制备了V2.1TiNi0.4Zr0.06Cu0.03M0.10(M=Cr, Co, Fe, Nb, Ta)储氢电极合金, 通过X射线衍射(XRD)、扫描电子显微镜(SEM)、电子衍射能谱(EDS)分析和电化学测试等手段系统研究了添加元素M对合金微结构与电化学性能的影响. 结果表明, 所有合金均由BCC结构的V基固溶体主相和C14型Laves第二相组成, 且第二相沿主相晶界形成三维网状分布; Cr、Nb 和Ta元素主要分布在合金主相中, 而Co和Fe元素主要分布在第二相中. 电化学性能测试表明, 在V2.1TiNi0.4Zr0.06Cu0.03合金中掺加Cr、Co、Fe、Nb或Ta元素后, 虽然会降低最大放电容量, 但能有效抑制合金中V和Ti的腐蚀溶出, 提高电极充放电循环稳定性; 同时还能明显改善合金的高倍率放电性能. 相比之下, V2.1TiNi0.4Zr0.06Cu0.03Cr0.10合金具有最佳的综合电化学性能.     

Theoretical study of molecular hydrogen and spiltover hydrogen storage on two-dimensional covalent-organic frameworks

Molecular hydrogen and spiltover hydrogen storages on five two-dimensional （2D） covalent-organic frameworks （COFs） （PPy-COF, TP-COF, BTP-COF, COF-18 A, and HHTP-DPB COF） are investigated using the grand canonical Monte Carlo （GCMC） simulations and the density functional theory （DFT）, respectively. The GCMC simulated results show that HHTP-DPB COF has the best performance for hydrogen storage, followed by BTP-COF, TP-COF, COF-18 A, and PPy-COE However, their adsorption amounts at room temperature are all too low to meet the uptake target set by US Department of Energy （US-DOE） and enable practical applications. The effects of pore size, surface area, and isosteric heat of hydrogen on adsorption amount are considered, which indicate that these three factors are all the important factors for determining the H2 adsorption amount. The chemisorptions of spiltover hydrogen atoms on these five COFs represented by the cluster models are investigated using the DFT method. The saturation cluster models are constructed by considering all possible adsorption sites for these cluster models. The average binding energy of a hydrogen atom and the saturation hydrogen storage density are calculated. The large average binding energy indicates that the spillover process may pro- ceed smoothly and reversibly. The saturation hydrogen storage density is much larger than the physisorption uptake of H2 molecules at 298 K and 100 bar （1 bar = 105 Pa）, and is close to or exceeds the 2010 US-DOE target of 6 wt% for hydrogen storage. This suggests that the hydrogen storage capacities of these COFs by spillover may be significantly enhanced. Thus 2D COFs studied in this paper are suitable hydrogen storage media by spillover.