过渡金属改善NaAlH4储氢性能的协同催化机理研究

It has attracted intensive attention in the field of renewable energy materials to catalytically enhance the kinetic properties of hydrogen ab/desorption of solid hydrogen storage materials. In this field, the investigation of high-performance nanocatalyst is one of the frontier research topics. Besides the design of new novel nanocatalyst, the research of fundamental understanding of the corresponding catalytic mechanism is also highly desired. In this proposal, we will carry out the first-principles studies on the co-catalytic mechanism of transition metals in enhancing hydrogen storage properties of NaAlH4 and design new nanocatalyst accordingly. On one hand, we will focus on studying the co-catalytic mechanism of co-doped transition metals in different configurations and different doping concentrations. On the other hand, we will examine the transition-metal doped carbon nanomaterials as new catalysts for improving the hydrogen storage performance of complex hydrides, which could be attributed to the cooperative effects between transition metals (having good catalytic properties) and carbon nanomaterials (having nanoconfinement/catalytic effects). The corresponding co-catalytic mechanisms for the above mentioned materials deserve comprehensive studies. On the basis of our detailed studies of the minimum energy paths of the transition-metal catalyzed reactions of hydrogen uptake/release of alanate (NaAlH4), the electronic and geometrical structures of transition states would be carefully analyzed. Combing the studies of the initial and final states, the corresponding catalytic mechanism would be concluded. We believe that our theoretical studies could benefit both fundamental studies and application researches for designing high-performance novel nanocatalyst, which would in turn benefit the studies of advanced hydrogen storage medium for on-board usage etc.

催化改善固体储氢材料充放氢过程的动力学性能是新能源领域的重要研究方向，其中探索新型高效的纳米催化材料更是近年来的前沿基础课题。本项目拟采用第一性原理方法，研究过渡金属改善NaAlH4储氢性能的协同催化机理，探索具有协同催化效果的新型纳米催化结构。一方面，通过改变过渡金属在NaAlH4中的掺杂浓度与掺杂种类，研究不同过渡金属催化成份在储氢材料充放氢过程中的协同催化作用，探究其中的催化机理；另一方面，利用过渡金属的催化作用和碳纳米材料的空间限域/催化功能协同改善NaAlH4的储氢性能，研究过渡金属与碳材料之间的协同催化机制。基于对过渡金属掺杂NaAlH4的充放氢反应通道的探索，对初末态和过渡态的几何结构及电子分布作详细研究，从原子层次上阐述过渡金属的催化机理和不同催化成份之间的协同催化作用，为新型储氢材料的实验和应用研究提供理论支持，促进新型纳米催化材料的设计与开发。

采用第一性原理和改进的Nudged Elastic Band Method 技术研究多种催化剂材料改善轻金属配位氢化物储氢性能的协同催化机理，探索具有协同催化效果的新型纳米催化结构。已取得的研究成果有：（1）以过渡金属Sc为例研究不同浓度的单质金属协同掺杂光滑Al(100)表面对材料氢化过程的影响。当Sc掺杂在最上层时，在Kubas相互作用机制的帮助下，提高掺杂浓度能够降低氢分子分解的反应势垒，但增大了氢原子扩散的难度；当Sc掺杂在次上层时，提高掺杂浓度能够降低材料完成整个氢化过程的能量势垒。同种催化剂材料协同催化机理的关键因素是氢分子和过渡金属以及铝原子的之间的电荷转移。（2）选择实验上已报道的催化剂，如Ti、Sc、Ce、Zr等元素共掺杂，探讨不同组分之间的优化组合形式及催化效果。在研究的所有组合中，Ti和Sc共掺杂时具有较好的协同催化效果，Sc和Ce共掺杂时的协同作用不明显。不同种类的过渡金属的原子半径、电负性、共价电子个数等因素共同影响催化剂材料的催化效果。（3）为探究二维纳米结构对储氢材料充放氢过程的限域/催化作用，研究了碳材料的电子性质，分析了单轴应力、简并扰动、以及二者共同作用时对石墨烯、硅烯材料电子性质的影响。（4）另外，在课题支持下，还采用基于广义梯度泛函的方法研究了碱基类似物的磁耦合特性、电子性质和光谱特性；采用Matlab计算了分子表面张力和温度的相关性，以上研究有助于拓展新的计算研究手段，提高对物理本质的理解。