多层核壳结构镁基纳米粒子构筑、调控与储氢机理研究

Mg-based nanocomposites prepared through the liquid phase reducing method possess good first hydrogen absorption/desorption kinetics properties. However, they suffer from poor cycle life and readily oxidation, due to poor thermal stability of nanoparticles. Targeting to these issues, this project proposes a new research idea of controllable fabrications of Mg-based hydrogen storage nanoparticle with multi-layer core-shell structure, Mg nano-particles as the core and combining catalytic layer and polymer layer as the shell. Monodispersed Mg nanoparticles with uniform size less than 10 nm can be prepared by controlling the reaction conditions. Transition metal catalytic layer provides a new hydrogen storage path for Mg core and plays a strong catalytic effect on the hydrogenation/dehydrogenation of Mg, to enhance the hydrogen storage kinetics and thermodynamic properties of the nano-particle. Encapsulation with hydrogen permeable oxygen nonpermeable polymer membrane is used to resist the oxidation on the high active nano-particle surface, to prevent the catalytic layer from falling off and to increase the cycle stability of hydrogen storage. This project will research deeply on the optimization of preparation process, the characterization of microstructure, the improvement of hydrogen storage property and the explanation of hydrogen storage mechanism. Study on effects of the interface bonding between core and shell, and the distribution state of catalytic layer and polymer layer on the hydrogen storage properties, which will play a role of guidance to instruct further optimization on hydrogen storage property of magnesium based material. Moreover, the innovative results achieved by this project will provide theoretical support and practical basis for the development of Mg-based hydrogen storage materials as an energy carrier in the practical application.

液相还原法制备的纳米镁基储氢材料具有较优异的首次吸放氢动力学性能，但仍面临循环寿命差、易氧化等问题，究其原因是纳米结构热稳定性较差。本项目针对此问题，提出了构筑多层核壳结构镁基纳米粒子的研究新思路：调控纳米Mg微观结构，筛选单分散、粒径均匀，颗粒小于10nm的纳米Mg（核）；利用过渡金属催化层为纳米Mg提供新的储氢路径，加快氢的离解和输运，降低吸放氢反应能垒，提高吸放氢反应速率，改善热力学稳定性；利用聚合物层的透氢抗氧性，提高高活性纳米颗粒的抗氧化能力，并通过聚合物层高弹塑性有效防止催化层脱落，从而提高吸放氢循环寿命。本项目将在制备工艺探索、微观结构表征、储氢性能改善和储氢机理阐明等方面开展深入系统的研究，探讨核-壳层间界面结合结构、催化层及聚合物层分布状态等对纳米Mg储氢性能的影响，为进一步优化镁基储氢体系提供科学依据，并为其作为能源载体的实用化提供理论支撑和实践基础。

镁基储氢材料具有储氢量大（7.6wt％）、环境友好、成本低等优点，在能源材料的开发方面得到了越来越多的关注，但是由于纯镁的吸放氢热力学及动力学性能较差，使其难以获得广泛的实际应用。纳米化是显著改善镁基储氢合金的热力学及动力学性能有效途径之一。但纳米镁基储氢材料在较高工作温度易发生团聚长大，很难保持稳定纳米结构，循环吸放氢性能较差，仍达不到实际应用的需求。结合纳米制备技术，通过适当手段，在纳米镁表面包覆一层聚合物、过渡金属，或限域于多孔载体材料，即可实现储氢路径调控，加快氢的离解和输运，又可增强纳米颗粒的抗再结晶能力，提高其吸放氢循环寿命。本研究采用液相还原法，制备单分散、核壳结构的纳米Mg基复合材料，旨在开发一种储氢量大，在室温可实现快速吸氢，放氢条件温和，循环寿命长，具有安全、稳定、防氧化特性的新型高性能纳米镁基储氢材料。研究发现过渡金属@Mg复合储氢材料吸放氢动力学最为优异，其储氢量>6.1wt.％，在50oC，甚至室温可以快速的低温吸氢，并且起始脱氢温度降低到216.8oC，且放氢激活能为93.8kJ/molH2。根据储氢机理分析，在加氢过程中形成的高含量γ-MgH2相有助于提高改善其脱氢动力学性能，并且TM元素可以解离氢和提供氢扩散快速通道。聚合物、多孔材料包覆纳米Mg复合材料储氢机制研究发现，聚合物、多孔材料可有效防止纳米Mg在吸放氢过程中团聚长大，显著改善纳米镁基储氢材料的循环稳定性，并且在一定程度改善纳米Mg的吸放氢动力学性能。