Mg-Nb及Mg-Nb2O5复合储氢材料粉体的制备及其性能

Synthesis and Properties of Mg-Nb and Mg-Nb2O5 Composite Hydrogen Storage Powders

摘要:

采用直流电弧等离子体法结合原位钝化法制备Mg-Nb和 Mg-Nb2O5复合储氢材料超细粉体，并利用ICP、XRD、TEM、P-C-T、TG-DTA等测试手段研究对比粉体的成分、相组成、微观形貌、颗粒粒径和吸放氢性能。ICP分析显示Mg-Nb粉中Nb含量高于Mg-Nb2O5粉，但均低于初始含量。XRD和TEM皆在Mg-Nb粉中发现MgNb2O3.67相，而Mg-Nb2O5中有NbO2.46新相生成。Mg-Nb粉的P-C-T曲线吸放氢平台更平坦，滞后更小；计算出Mg-Nb粉的氢化生成焓为–73.33 kJ/mol H2，低于Mg-Nb2O5粉的–82.45 kJ/mol H2。氢化后粉体的TG-DTA分析，Mg-Nb粉的放氢峰更尖锐，放氢速度更快。Mg-Nb粉体更佳的热力学和动力学性能证明钝化引入的氧化物MgNb2O3.67起到了催化作用，而Mg-Nb2O5中的NbO2.46由于含量少、分布不均匀等原因催化效果差。以上结果证明经过钝化获得氧化物的催化效果好于直接电弧蒸发

Abstract:

The Mg-Nb and Mg-Nb2O5 hydrogen storage composite powders were prepared through arc plasma method followed by in-situ passivation. The composition, the phase component, the morphology, the particle size and the hydrogen storage properties of two powders were systematically analyzed by using inductive coupled plasma emission spectrometer (ICP), X-ray diffraction (XRD), transmission electron microscopy (TEM), pressure-composition-temperature (PCT) and thermogravimetry/differential thermal analysis (TG/DTA) techniques. ICP analyses reveal that the Nb contents of both powders reduce compared with their initial compositions. In addition, Nb content in Mg-Nb powder is higher than that in Mg-Nb2O5 powder. XRD results show that MgNb2O3.67 phase exists in Mg-Nb powder and NbO2.46 phase in Mg-Nb2O5 powder. TEM observations reveal that the MgNb2O3.67 particles are distributed more homogeneously and their particle sizes are smaller than those of the NbO2.46 particles in Mg-Nb2O5 powder. PCT analyses show that the hydrogen sorption plateaus of the Mg-Nb powder are wider and smoother with a smaller absorption/desorption gap compared to those of Mg-Nb2O5 powder. Based on Van’t Hoff equation, the hydrogenation enthalpy of the Mg-Nb powder is determined to be –73.33 kJ/mol H2, lower than the value of –82.45 kJ/mol H2 for Mg-Nb2O5 powder. TG-DTA measurements show that the hydrogenated Mg-Nb powder has a faster desorption rate and a sharper endothermic desorption peak compared to those of the hydrogenated Mg-Nb2O5 powder. The better hydrogen storage thermodynamic and kinetic properties of Mg-Nb powder may be attributed to the catalytic effect of MgNb2O3.67 generated in passivation. In contrast, the NbO2.46 phase can be reduced during hydrogenaing. Also, it has a low content and a heterogeneous distribution in Mg-Nb2O5 powder and thus possesses a poor catalytic effect. The above results show that the arc plasma method followed by in-situ passivation is an more efficient approach to produce metal-oxide hydrogen storage composite with a superior catalytic effect of oxide compared with the directly evaporated oxide