Enhancement of the hydrogen storage properties of Mg/C nanocomposites prepared by reactive milling with molybdenum

The effect of Mo on the morphology, crystal structure and hydrogen sorption properties of Mg/C composites prepared by reactive milling was studied. Transmission electron microscopic(TEM) observation shows that Mg/C composites prepared with the addition of Mo are of nanoscale with particle size about 20-120 nm after 3 h of milling under 1 MPaH_2. MgH_2 of tetrahedral crystal structure predominates in the materials with the geometric shape of oblique hexagonal prism. From X-ray diffraction(XRD) and hydrogen content studies, Mo and crystallitic carbon have a synergistic effect on promoting the hydrogenation rate in the reactive milling process. From differential scanning calorimetric(DSC) studies, the dehydrogenation peak temperature of the Mg/C materials with Mo is lowered to 299-340 ℃.     

无烟煤和烟煤在镁基储氢材料制备中的作用

在纯镁中加入无烟煤通过机械球磨的方法制备镁基储氢材料。对制备的储氢材料的形貌和储氢性能进行表征和测试。结果表明,在镁中添加无烟煤进行机械球磨可以在1.5 h内生成纳米级颗粒,但是添加量过高会降低材料的储氢量,70Mg30C的储氢量为550 mL/g,60Mg40C的储氢量为360 mL/g。在制备的储氢材料中加入烟煤之后,在500℃热处理条件下,储氢材料出现熔融现象,且熔融的烟煤都包覆在颗粒表面。     

二硫化钼助磨的镁基储氢材料相结构及储氢性能

本研究在氩气气氛保护下球磨镁和二硫化钼混合粉末制备了镁基储氢材料。利用X射线衍射、差示扫描量热分析等测试手段对储氢材料的相结构和储氢性能进行了测定。结果表明,球磨2.5 h只需添加10 wt.%的二硫化钼即可有效地防止镁冷焊现象的发生,球磨3.0 h则需要添加15 wt.%的二硫化钼;二硫化钼在球磨过程中由晶体转变为非晶体;二硫化钼不参与储氢,不破坏镁的晶体结构;添加10 wt.%的二硫化钼制备的储氢材料,其储氢密度可达到5.8 wt.%以上;二硫化钼的添加对于降低材料的放氢温度无明显影响。     

过渡金属氟化物改善2NaBH_(4)+MgH_(2)储氢体系的放氢热力学性能EI北大核心CSCD

通过机械球磨法制备了2NaBH_(4)+MgH_(2)和2NaBH_(4)+MgH_(2)+0.1MF_(x)(M=Ni,Ti,Zr;x=2,3,4)储氢复合材料。分别通过扫描电子显微镜(SEM)、能谱分析仪(EDS)和X射线衍射(XRD)分析了复合材料的形貌、元素分布和晶体结构。另外,通过差示扫描量热法(DSC)和程序升温脱附(TPD)测试了材料的放氢热力学性质。结果表明,通过添加NiF_(2),TiF_(3)和ZrF_(4),分别将2NaBH_(4)+MgH_(2)的第一个放氢峰温降低了8.9,35.7℃和54.5℃。此外,放氢过程中出现的NaMgF_(3)相改变了第一个放氢过程的反应路径,并且改变了2NaBH_(4)+MgH_(2)的第二次放氢过程,使得第二个脱氢过程的峰温分别降低了18.0,31.1℃和34.1℃。添加NiF_(2),TiF_(3)和ZrF_(4)使2NaBH_(4)+MgH_(2)的放氢比例分别达到91.7%,91.9%和98.7%。其中ZrF_(4)对2NaBH_(4)+MgH_(2)的整个放氢过程显示出了最好的效果。因此,2NaBH_(4)+MgH_(2)+0.1ZrF_(4)可以作为燃料电池供氢系统的潜在应用体系。     

Crystal structure and hydrogen storage behaviors of Mg/MoS<Subscript>2</Subscript> composites from ball milling

The Mg/MoS₂ composites were prepared by ball milling under argon atmosphere, and the effect of MoS₂ on the crystal structure and hydrogen storage properties of Mg was investigated. It is found that 10 wt% of MoS₂ is sufficient to prevent particle aggregation and cold welding during the milling process. The crystallite size of Mg will remain constant at slightly less than 38.8 nm with the milling process due to the size confinement effect of MoS₂. The dehydrogenation temperature of MgH₂ is reduced to 390.4-429.4 °C due to the crystallite size reduction. Through fitting by Johnson-Mehl-Avrami model, it is found that Mg crystal grows by three dimension controlled by interface transformation during the process of MgH₂ decomposition. MoS₂ has a weak catalyst effect on the decomposition of MgH₂ and activation energy of 148.9 kJ/mol is needed for the dehydrogenation process calculated by the Arrhenius equation.     

蛋白质、多肽及氨基酸与蒙脱石复合的分析表征

研究蛋白质类活性物质在蒙脱石表面的结合形式及状态对药物的吸附及运输等研究具有重要意义。本次实验主要研究了不同pH值下,蛋白质、多肽和氨基酸分别与蒙脱石相互作用后,复合物的X射线衍射(XRD)、红外光谱(FT-IR)和热重(TG)等分析表征。结果表明,蛋白质、多肽、氨基酸对蒙脱石层间距的改变明显差异,有机物的存在状态及与蒙脱石片层的作用力强度明显不同;pH值对不同组分插层效果的影响也有较大差异。可以认为,不同形态的有机大分子的分子体积、分子量直接决定了其与蒙脱石的作用强度及其存在状态。     

变压和恒压加氢模式下CO2杂质对镁储氢性能的影响

金属镁资源丰富且储氢量大,是有大规模应用前景的储氢材料,但镁易与CO_2等杂质气体反应生成致密的MgO和碳薄膜覆盖在镁颗粒表面而阻碍吸氢,研究变压加氢和恒压加氢过程中钝化膜影响镁吸氢的机制对优化加氢操作有重要意义。等温吸附测试表明,在含1.0%(摩尔分数)CO_2杂质的氢气中于340℃、5 h恒压加氢时,吸氢量降至2.32%(质量分数),而变压加氢时吸氢量降至1.09%(质量分数)。XRD分析表明两种加氢模式下CO_2均会与Mg反应生成晶态MgO;HRTEM观测表明MgO膜紧密附着在镁颗粒表面;XPS分析表明除了生成MgO外,还有单质碳生成,以及C—O和■基团化学吸附于镁颗粒表面。热力学计算表明,变压加氢过程中在低于吸氢平台压的低压阶段,CO_2与Mg反应生成致密的钝化膜,从而阻碍高压阶段Mg与H_2反应生成MgH_2,致使吸氢量较低;而恒压加氢时,初始氢压高于吸氢平台压,CO_2和H_2与Mg竞争反应,从而吸氢量高于变压加氢模式的吸氢量。