过渡金属掺杂石墨烯和固溶镍改善Mg41RE5型Mg基纳米晶/非晶合金储氢性能的机理研究

The application of Mg-based materials with high hydrogen storage capacity is hindered by poor kinetics of hydrogen absorption and desorption reaction and high reaction temperature. In this project, the hydrogen storage kinetics and thermodynamic properties of Mg-based nanocrystalline/amorphous alloys will be improved by combining alloying, nanocrystallization, catalysis and composite strategies to form hydrogen diffusion channels with similar network structures, increase nanocrystalline grain boundaries and catalytic active sites, and reduce the binding energy between materials and hydrogen. Firstly, the Mg-RE-Ni ternary alloy system will be optimized on the basis of previous studies. A small amount of Ni solute will be added in the alloying process of Mg41RE5, and then the alloys mixed with M-doped graphene (GR, transition metal elements M=Fe, Ni, Cu) will be milled to prepare Mg-RE-Ni-GR composite hydrogen storage materials, which is characterized with GR supported or inserted an amorphous/nanocrystalline alloy. The effects of microstructure turning, solid solution nickel content and M-doped graphene on hydrogen storage properties will be investigated. The phase transition, nucleus formation and growth mechanism during hydrogen absorption and desorption reaction will be analyzed. The synergistic catalytic mechanism and spatial confinement of various phases in the hydrogen absorption and desorption process of Mg will be researched. The mechanism of improving the hydrogen storage kinetics and thermodynamic of the composites will be studied in detail, which will provide a theoretical basis for the preparation of Mg-based hydrogen storage composites with excellent hydrogen absorption and desorption properties.

高储氢容量Mg基材料因吸放氢动力学差和反应温度高而阻碍了其实际应用。本项目拟通过联合合金化-纳米化-催化-复合多种策略为一体，在合金中形成类似网状结构的氢扩散通道、增加纳米晶晶界和催化活性位点、降低材料与氢的结合能，从而同时改善Mg基纳米晶/非晶合金的储氢动力学和热力学性能。首先在前期研究基础上优化Mg-RE-Ni三元合金体系，在Mg41RE5合金化过程中固溶少量Ni熔炼，再与不同过渡金属元素M(M=Fe、Ni、Cu)掺杂的石墨烯(GR)混合球磨，制备出GR镶嵌和负载非晶/纳米晶合金的Mg-RE-Ni-GR复合储氢材料。研究微观结构控制、固溶镍含量和掺杂石墨烯对材料储氢性能的影响；分析吸放氢反应过程中的相转变、晶核的形成及长大机制；深入研究多种物相在Mg吸放氢过程中的协同催化机理及限域作用。阐明复合材料的储氢动力学及热力学改善机理，为制备具有优异吸放氢性能的镁基储氢材料提供理论依据。

高储氢容量Mg基材料因吸放氢动力学差和反应温度高而阻碍了其实际应用。通过联合合金化-纳米化-催化-复合多种策略，在合金中形成类似网状结构的氢扩散通道、增加纳米晶晶界和催化活性位点、降低材料与氢的结合能，从而同时改善Mg基纳米晶/非晶合金的储氢动力学和热力学性能。.项目通过真空感应熔炼制备高镁含量的稀土—镁—镍合金。然后将稀土—镁—镍合金与石墨烯混合球磨，制备了具有优异动力学性能并且氢化物稳定性较低的纳米晶储氢复合材料，详细研究了其贮氢性能。合金经氢化/脱氢后形成的MgH2-Mg2NiH4/Mg2Ni-REHx纳米复合材料，在Mg2Ni/Mg2NiH4和REHx的双重催化作用下表现出优异的动力学性能，其可逆吸氢量为5.62 wt.% H2。随着球磨时间的延长，合金的微观结构逐渐由多晶向纳米晶和非晶转变。球磨引入的纳米晶晶界为氢扩散提供了更多的通道，从而增强了球磨态合金的储氢动力学。Sm5Mg41 + x wt.% NG (x = 0、2、4、8、12)复合材料吸氢后出现纳米级的Sm3H7和MgH2相，NG以纳米片的形式镶嵌在复合材料的表面。在脱氢样品中可以观察到纳米晶Mg和一些微观缺陷，包括孪晶、晶界和位错。这种微观缺陷和纳米晶边界可以降低吸放氢反应过程中需要克服的总势垒，从而提高合金的储氢动力学。对于x = 2、4、8、12的复合材料，其放氢活化能分别为132.08、128.06、112.90和112.35 kJ/mol H2。吸氢焓变分别为-79.18、-78.09、-76.30、-76.10 kJ/mol H2，表明NG的加入对复合材料的热力学性能有微弱的提高。Mg-Ce-Y + x wt.% Fe@C (x = 1、3、6、10)复合材料表现出了优异的吸放氢动力学性能，这归因于具有高缺陷密度、高比表面积和高催化活性的Fe@C的协同催化作用。.通过对本项目研究，掌握了具有优异吸放氢性能的Mg41RE5型稀土—镁—镍+石墨烯的非晶/纳米晶储氢复合材料制备方法。探索了吸放氢过程中各相的变化，并构建吸放氢反应路径。阐明了稀土元素、镍含量、熔炼+球磨工艺及掺杂石墨烯对合金相组成、微观结构及吸放氢动力学、热力学的影响及改善机理。为制备具有优异吸放氢性能的镁基贮氢合金提供理论依据。