基于核壳结构的纳米镁基氢化物复合体系构建与储氢性能研究

The exploration of Mg-based hydrides for the storage and transportation of hydrogen has attracted immense research interests. High operating temperature, the slow kinetics for reversible hydrogen storage reaction and unsatisfied cycling stability, however, significantly obstruct their applications. Although nanoconfinement serves as an effective and efficient method to improve the hydrogen storage performance of Mg-based hydrides, the synergistic achievement of both high storage density and stable cycling performance remains a big challenge. In order to solve it, we propose the controllable synthesis of core-shell Mg(BH4)2@MgH2 nanoparticles by tuning the reaction between B2H6 and homogeneous MgH2 nanoparticles to some extent under the support of graphene. Taking advantage of the catalysis and the structural support role of graphene, the combination of Mg(BH4)2 with a high storage density of 14.9 wt.% and MgH2 with a stable cycling life on a nanoscale level is able to obtain a hybrid system with high hydrogen storage density, stable cycling performance and superior dehydrogenation/hydrogenation kinetics. More importantly, the partial transformation of MgH2 nanoparticles into Mg(BH4)2 nanoparticles is capable of further downsizing the particle size of MgH2 and tuning the size of the thus-formed Mg(BH4)2 simultaneously, which plays an important role in improving the hydrogen storage properties of both MgH2 and Mg(BH4)2, including thermodynamics and kinetics. Based on both experimental and theoretical results, the relationship between the structure and the composition of core-shell Mg(BH4)2@MgH2 nanoparticles, the hydrogenation and dehydrogenation kinetics, and the cycling stability will be revealed. Hence, the outcomes of this project will provide some insights into the design and modification of Mg-based hydrides.

镁基氢化物一直是固态储氢领域的研究热点和重点，然而，工作温度高、动力学性能差和循环不稳定等问题限制了它的实际应用。纳米空间限域可以有效改善单一镁基氢化物的动力学性能，但是如何平衡体系的可逆容量和循环稳定性一直是该技术应用面临的难点。本项目提出利用石墨烯支撑的纳米MgH2颗粒为功能化反应基体，通过调控MgH2与B2H6间的固气反应，将部分MgH2原位转换成Mg(BH4)2，进而构建具有核壳结构的纳米Mg(BH4)2@MgH2复合体系，协同提高储氢容量、循环稳定性和吸/放氢动力学性能。核壳结构的构筑可以同时调控MgH2和Mg(BH4)2的结构与尺寸，有助于获得优异的动力学和热力学性能，从而进一步降低复合体系的吸/放氢温度，改善可逆吸/放氢性能。本项目将结合实验与理论研究，在纳米尺度上揭示组分与结构-吸/放氢动力学-循环稳定性之间的内在关系，对开发新型镁基储氢材料有一定的学术意义及应用参考价值。

镁基氢化物一直是固态储氢领域的研究热点和重点，然而，工作温度高、动力学性能差和循环不稳定等问题限制了它的实际应用。纳米空间限域可以有效改善单一镁基氢化物的动力学性能，但是如何平衡体系的可逆容量和循环稳定性一直是该技术应用面临的难点。本项目利用石墨烯支撑的纳米MgH2颗粒为功能化反应基体，通过调控MgH2与B2H6间的固气反应将部分MgH2原位转换成Mg(BH4)2，构建了具有核壳结构的纳米Mg(BH4)2@MgH2复合体系，协同提高了储氢容量、循环稳定性和吸/放氢动力学性能。通过理论与实验研究证明，MgH2可以起到“氢泵”的作用，促进MgB2中稳定B-B键的破坏以及B-H键的可逆生成，大幅提高了Mg(BH4)2的可逆储氢性能。同时，石墨烯的均匀分布抑制了Mg(BH4)2@MgH2纳米颗粒在循环过程中的团聚，提高了复合体系的循环稳定性。所研制的Mg(BH4)2@MgH2复合体系在8次循环后仍具有约为4.8 wt.%的循环储氢容量。本项目成果对开发新型镁基储氢材料有一定的学术意义及应用参考价值。