核壳结构硼基储氢材料催化体系的可调控性构建及机理研究

Boron-based hydrogen storage materials comprised of light-weight elements have received much attention as high solid-state hydrogen storage candidates recently. To achieve this, the key is how to establish tunable de/rehydrogenation systems under moderate conditions, which strongly depends on the thermodynamic and kinetics during the interaction process between hydrogen and materials. This project aims at the establishment of core-shell structural catalytic LiBH4@SiB4 systems with high hydrogen density, low temperature, controllable kinetics, superior reversibility and high air-stability. And it will study the hydrogen storage tunability and key factors on influencing the hydrogen storage performance. The composition and morphology of LiBH4@SiB4 would be optimized for improving the hydrogen storage kinetics and reversibility properties through accurately controlling the preparation process, so as to reveal the relationship of process-microstructure-property. Focusing on the mechanism of de/rehydrogenation process and property degradation, this project will combine the experimental observations and theoretical calculations to clarify the phase transformation, structure change, electron transfer, diffusion of atom/molecule, hydrogen exchange and boron exchange effect, etc. Then, the catalytic models of de/rehydrogenation will be constructed, which will play an important role on instructing further optimization of hydrogen storage property of LiBH4. The research results will demonstrate important experimental support and theoretical guidance for application of boron-based materials as high capacity hydrogen storage candidates.

由轻质元素构成的硼基储氢材料是实现高容量固态储氢的研究热点，其关键是能否构建在温和条件下的可控吸放氢体系，本质是氢与材料相互作用过程的热力学和动力学问题。本项目拟通过构建核壳结构LiBH4@SiB4催化储氢体系，研究储氢性能的可调控性及决定因素，开发具有高储氢密度、近室温操作、可控吸放氢、寿命长和空气稳定性高的复合材料。通过工艺参数调控催化体系的成分和微观结构，研究核壳结构成分和微观结构对改善LiBH4动力学和循环性能的作用，揭示材料体系工艺-结构-性能的内在联系；重点围绕LiBH4催化体系的吸放氢机理和性能衰减机制，阐明氢与材料相互作用过程中的物相转变、结构变化、电子转移、原子/分子扩散、氢交换和硼交换效应等基础问题；从而建立吸放氢催化反应模型，为优化硼基储氢材料性能提供科学依据。本项目将为探索高容量硼基储氢材料体系提供重要的实验支撑和理论指导，并提升LiBH4作为固态储氢材料的潜能。

本项目针对轻质高容量配位氢化物储氢材料，如硼氢化锂和铝氢化钠，存在的放氢温度高、动力学差和不可逆性的问题，围绕材料制备工艺-微观组织结构-储氢性能的内在联系，开展对配位氢化物的储氢性能调控研究。项目重点探索氢与材料之间相互作用过程中的电子转移和原子/分子扩散，以及调控储氢材料复合体系动力学的基础科学问题。本项目初步弄清具有不同化学态的金属硼化物（SiB4/FeB/TiB2）对硼氢化锂再生过程（即可逆吸氢反应）的影响和机制。研究发现，SiB4(s) + 4LiH(s) + 6H2(g) = 4LiBH4(s) + Si(s)是一个具有良好的可逆性的储氢化学反应。SiB4化合物对于LiBH4的吸放氢过程具有双重效用。在LiBH4放氢过程中，SiB4充当催化剂的角色而促进LiBH4的分解放氢过程；在350oC下，体系的放氢容量高达2.24 at.H/f.u. LiBH4，表现出良好的放氢动力学性能。在LiBH4的氢化再生过程，SiB4则作为反应剂参与LiBH4的生成过程，从而改善LiBH4的氢化再生进程；在400oC和10 MPa H2下，LiBH4的可逆容量为2.16 at. H/f.u. LiBH4，表现出良好的可逆性。此外，采用物理/化学协同吸附效应的思路，构建了石墨烯和铈共掺杂的铝氢化钠复合体系，形成石墨烯和铈的协同催化作用，铝氢化钠的放氢温度可降低至85oC，200oC下放氢容量达5.06wt%，可逆容量保持94.7%，表现出良好的储氢性能。本项目的研究工作为探索具有优良储氢性能的配位氢化物储氢材料复合体系提供了较好的研究思路。