含二聚体的二维过渡金属化合物的设计及其物理化学特性研究

The direct way to develop new 2D materials is to change their structural units. The widely studied 2D transition metal materials, such as Ti2C, MoS2, and MoN2, they all have atoms as their structural units. When going beyond this point by using some molecules or clusters with novel properties as structural units, some unconventional new materials can be obtained. Inspired by the fact that the dimers of C2, S2 and N2 display very different traits from their atoms, and widely exist in organic molecules, clusters and bulk phases, in this project, we will explore 2D transition metal materials containing dispersed C2, S2 and N2 dimers, respectively, by using our recently developed “bonding-restricted structure search” method. We will systematically study their structural stability, electronic structures, characteristics of adsorption and activation, and catalytic performance for CO and CO2, transport and thermoelectric properties. Meanwhile, we will investigate the micro-mechanisms govern the properties, and the potential applications in energy and environment. This project can not only expand the 2D family and their applications, but also provide theoretical support for experimental synthesis.

研发新型二维材料最直接的切入点是改变“结构单元”。目前备受关注的二维过渡金属化合物（如: Ti2C, MoS2, MoN2等）都是以原子为结构单元，若能突破这一界限，使用一些性质优异的分子或纳米团簇为结构单元便可构建新型二维材料。由于C2、S2、N2等二聚体具有与其单原子非常不同的化学性质，并广泛地存在于有机分子、团簇及一些块体材料中，本课题将以二聚体X2（X=C, S, 和 N）为结构单元,利用我们课题组最近发展的“成键受限结构搜索”程序,设计含有分离的二聚体X2单元的二维新型过渡金属化合物MX2；系统地研究这类材料二维晶体结构的稳定性、电子结构、吸附与反应动力学、输运和热电性质等；重点研究这类新型材料的储氢、CO和CO2的吸附、活化与催化转化特性；探索其微观机理和在能源与环境方面的应用前景，以拓广二维材料家簇及其应用领域，为新材料的研发和实验合成提供理论支撑。

常规的二维材料（石墨烯、硅烯、硼烯、BN单层、MoS2,、Ti2C等）均以原子为基本结构单元, 根据“结构-功能”关系，我们改变“结构基元”，系统地开展了以“原子二聚体”为结构基元的二维新材料设计、性质及应用研究。我们采用结构基元法、结构搜索法结合第一性原理计算和分子动力学模拟，不仅设计了项目申请书中建议的以二聚体C2, S2和N2为结构基元的多种二维材料，而且还设计和研究了含二聚体P2，B2，Si2，Se2多种二维新材料。这些材料由于其独特的几何结构，表现出丰富的物理化学性质，包括半导体特性、拓扑半金属、金属性，负泊松比、高能量密度、高温铁磁性、高极化率、强二次谐波产生等；并有着广泛的应用前景。如：仅含sp2杂化碳原子的半导体新型二维碳材料PCF-graphene, 在可见光范围内透明且对紫外光有好的吸收，可应用于光学器件；含S2二聚体的二维材料Penta-ZnS2，由于其半导体特性和二次谐波非线性光学效应，可望在微纳光电器件中有很好的应用；含N2二聚体的二维材料penta-MnN2具有高居里温度和强的铁磁性，可望应用于自旋电子学器件。这些研究不仅极大地扩展了二维新材料体系，而且为新型能源材料、环境材料和多功能材料的研发提供了新的思路。