Fundamental Aspects of Materials and Energy, Department of Radiation, Radionuclides and Reactors, Faculty of Applied Sciences, Delft University of Technology, Delft, The Netherlands.
J Am Chem Soc. 2013 May 29;135(21):7891-900. doi: 10.1021/ja3123416. Epub 2013 May 15.
Spark discharge generation was used to synthesize Mg-Ti nanocomposites consisting primarily of a metastable body-centered-cubic (bcc) alloy of Mg and Ti. The bcc Mg-Ti alloy transformed upon hydrogenation into the face-centered-cubic fluorite Mg1-yTiyHx phase with favorable hydrogen storage properties. Both metal and metal hydride nanocomposites showed a fractal-like porous morphology, with a primary particle size of 10-20 nm. The metal content of 70 atom % (at %) Mg and 30 at % Ti, consistently determined by XRD, TEM-EDS, and ICP-OES, was distributed uniformly across the as-prepared sample. Pressure-composition isotherms for the Mg-Ti-H nanocomposites revealed large differences in the thermodynamics relative to bulk MgH2, with a much less negative enthalpy of formation of the hydride as small as -45 ± 3 kJ/molH2 as deduced from van't Hoff plots. The plateau pressures of hydrogenation were substantially higher than those for bulk MgH2 in the low temperature range from 150 to 250 °C. The reaction entropy was simultaneously reduced to values down to 84 ± 5 J/K mol H2, following a linear relationship between the enthalpy and entropy. Plausible mechanisms for the modified thermodynamics are discussed, including the effect of lattice strains, the presence of interfaces and hydrogen vacancies, and the formation of excess free volume due to local deformations. These mechanisms all rely on the finely interdispersed nanocomposite character of the samples which is maintained by grain refinement.
火花放电生成法用于合成主要由 Mg 和 Ti 的亚稳体心立方 (bcc) 合金组成的 Mg-Ti 纳米复合材料。bcc Mg-Ti 合金在加氢后转化为具有良好储氢性能的面心立方萤石 Mg1-yTiyHx 相。金属和金属氢化物纳米复合材料均表现出类分形多孔形态，一次颗粒尺寸为 10-20nm。金属含量为 70 原子%（at%）Mg 和 30 at%Ti，通过 XRD、TEM-EDS 和 ICP-OES 一致确定，在制备的样品中均匀分布。Mg-Ti-H 纳米复合材料的压力-组成等温线显示出与大块 MgH2 相比热力学性质的巨大差异，形成氢化物的焓变非常小，仅为-45±3kJ/molH2，这可以从范特霍夫图推断得出。与大块 MgH2 相比，在 150 至 250°C 的低温范围内，加氢的平台压力要高得多。反应熵同时降低到 84±5J/K mol H2，遵循焓和熵之间的线性关系。讨论了改进热力学的合理机制，包括晶格应变、界面和氢空位的存在以及局部变形导致的过剩自由体积的形成。这些机制都依赖于样品的精细分散纳米复合材料特性，这种特性通过晶粒细化得以保持。
