Structural and electrochemical properties of high-capacity Ml-Mg-Ni-based hydrogen storage alloys

The Ml-Mg-Ni-based (Ml = La-rich mixed lanthanide) hydrogen storage alloy Ml_0.88Mg_0.12Ni_3.0-Mn_0.10Co_0.55Al_0.10 was prepared by inductive melting. The micro-structure was analyzed by XRD and SEM. The alloy consists mainly of CaCu₅-type phase, Ce₂Ni₇-type phase and Pr₅Co₁₉-type phase. The electrochemical measurements show that the maximum discharge capacity is 386 mAh/g, 16.3% higher than that of the commercial AB₅-type alloy (332 mAh/g). At discharge current density of 1 100 mA/g, high rate dischargeability is 62%, while that of the AB5-type alloy is only 45%. The discharge capacity decreases to 315 mAh/g after 300 charge/ discharge cycles, 81.5% of the maximum discharge capacity. __________ Translated from Journal of Xi’an Jiao Tong University, 2008, 42(3) (in Chinese)     

基片温度对LiCoO2薄膜结构与电化学性能的影响

采用射频(RF)磁控溅射技术制备了用于全固态薄膜锂电池的非晶态和多晶LiCoO2阴极薄膜,利用XRD和SEM研究了沉积温度对LiCoO2薄膜结构和形貌的影响,并研究了高温退火后薄膜的电化学性能.研究结果表明,随著基片温度的不同,薄膜成分、表面形貌以及电化学行为有明显差异.室温沉积的薄膜很难消除薄膜中Li2CO3的影响,经过高温退火处理后也无法形成有效的多晶LiCoO2薄膜,而150℃沉积的薄膜经过高温退火后形成了有利于锂离子嵌入的多晶LiCoO2结构,薄膜显示出了较好的电化学性能.     

Effect of Ni,Fe and Fe-Ni alloy catalysts on the synthesis of metal contained carbon nano-onions and studies of their electrochemical hydrogen storage properties

Three types of carbon nano-onions(CNOs) including Ni@CNOs.Fe_3C@CNOs and Fe_(0.64)Ni_(0.36)@CNOs nanoparticles have been synthesized by catalytic decomposition of methane at 850 ℃ using nickel,iron and iron-nickel alloy catalysts.Comparative and systematic studies have been carried out on the morphology,structural characteristics and graphitic crystallinity of these CNOs products.Furthermore,the electrochemical hydrogen storage properties of three types of CNOs have been investigated.Measurements show that the Ni@CNOs have the highest discharge capacity of 387.2 mAh/g,coiTesponding to a hydrogen storage of 1.42%.This comparison study shows the advantages of each catalyst in the growth of CNOs.enabling the controllable synthesis and tuning the properties of CNOs by mediating different metals and their alloy for using in the fuel cell system.     

Effect of Ni,Fe and Fe-Ni alloy catalysts on the synthesis of metal contained carbon nano-onions and studies of their electrochemical hydrogen storage properties

Three types of carbon nano-onions(CNOs) including Ni@CNOs.Fe_3C@CNOs and Fe_(0.64)Ni_(0.36)@CNOs nanoparticles have been synthesized by catalytic decomposition of methane at 850 ℃ using nickel,iron and iron-nickel alloy catalysts.Comparative and systematic studies have been carried out on the morphology,structural characteristics and graphitic crystallinity of these CNOs products.Furthermore,the electrochemical hydrogen storage properties of three types of CNOs have been investigated.Measurements show that the Ni@CNOs have the highest discharge capacity of 387.2 mAh/g,coiTesponding to a hydrogen storage of 1.42%.This comparison study shows the advantages of each catalyst in the growth of CNOs.enabling the controllable synthesis and tuning the properties of CNOs by mediating different metals and their alloy for using in the fuel cell system.     

Behavior of the ferroelectric polarization as a function of temperature in sol-gel derived strontium bismuth tantalate thin films

Strontium bismuth tantalate (SBT) thin films of nominal composition Sr_0.8Bi_2.2Ta₂O₉ have been prepared on (111)Pt/TiO₂/SiO₂/(100)Si substrates by Chemical Solution Deposition (CSD) methods, using two different thermal treatments of crystallization. The evolution of the ferroelectric polarization as a function of temperature has been studied using hysteresis loops, thermo stimulated current (TSC) measurements and the evolution of the pyroelectric coefficient (γ_M) with temperature. The results of remnant polarization (P _r) obtained from hysteresis loops and γ_M as a function of temperature showed different trends, indicating the presence of polarizing bias field in the prepared thin films due to induced asymmetry of the electrical and mechanical conditions produced at the top and bottom film electrode interfaces. The competition between internal bias fields due to differences in contact potentials of bottom and top electrodes and flexoelectric bias fields induced by stress gradient, can be in the origin of the γ_M fluctuation with temperature. A critical temperature (T ^*) is found that can be explained as the crossover between the dominant effects. It can be related to a possible ferroelectric-ferroelectric phase transition previously reported. The results also indicate that the P _r is not stable for temperatures over ≈425 K.     

Tb2–xNdxZn17–yNiy (x = 0.5, y = 4.83): a new intermetallic with a maximum disordered structure and its hydrogen storage properties

The ternary Tb_2–xNd_xZn_17–yNi_y (x = 0.5, y = 4.83) disordered phase belongs to the structural family based on the rhombohedral Th₂Zn₁₇ structure type. The structure is maximally disordered since all the sites are occupied by statistical mixtures of atoms. The Tb/Nd mixture of atoms occupies the 6c site (site symmetry 3m). The statistical mixtures Ni/Zn consisting of more Ni atoms are located in the 6c and 9d (symmetry .2/m) sites. In the following 18f (site symmetry .2) and 18h (site symmetry .m) sites are located Zn/Ni statistical mixtures which consist of more Zn atoms. Zn/Ni atoms form three-dimensional networks with hexagonal channels that fill statistical mixtures of Tb/Nd and Ni/Zn. The Tb_2–xNd_xZn_17–yNi_y compound belongs to the family of intermetallic phases capable of absorbing hydrogen. In the structure, there are three types of voids, namely, 9e (site symmetry .2/m), 3b (site symmetry m) and 36i (site symmetry 1), in which hydrogen can be inserted, and the maximum total absorption capacity can reach 1.21 wt% H₂. Electrochemical hydrogenation shows that the phase absorbs 1.03% of H₂, which indicates partial filling of the voids with H atoms.     

Sorption and desorption properties of a CaH2/MgB2/CaF2 reactive hydride composite as potential hydrogen storage material

The hydrogenation behavior of 3CaH₂+4MgB₂+CaF₂ composite was studied by manometric measurements, powder X-ray diffraction, differential scanning calorimetry and attenuated total reflection infrared spectroscopy. The maximum observed quantity of hydrogen loaded in the composite was 7.0 wt%. X-ray diffraction showed the formation of Ca(BH₄)₂ and MgH₂ after hydrogenation. The activation energy for the dehydrogenation reaction was evaluated by DSC measurements and turns out to be 162±15 kJ mol⁻¹ H₂. This value decreases due to cycling to 116±5 kJ mol⁻¹ H₂ for the third dehydrogenation step. A decrease of ca. 25–50 °C in dehydrogenation temperature was observed with cycling. Due to its high capacity and reversibility, this composite is a promising candidate as a potential hydrogen storage material.