无序碳单层的电子结构及氢原子吸附的第一性原理

本研究运用第一性原理计算方法,系统地研究了无序碳单层材料不同位点的电子结构及其析氢性能.计算结果显示无序结构中的C-C键相比于石墨烯中的C-C键在26.7%的范围内有不同程度的拉伸或压缩,使得C原子电荷在-0.17～+0.16个电子范围内变化,导致部分C原子电子局域化.电子的局域化增强了C原子的化学活性,从而表现出了较强的吸附性能.我们发现H原子与C原子的键合及析氢性能与C原子间的键角相关.对于三配位的碳原子,其中三个价电子通过sp~2杂化轨道与最邻近的碳原子结合形成较强的共价键,而余下的一个p_z轨道电子可以与H原子在垂直于原子层的方向形成较弱的化学键.无序结构可以打破三个sp~2杂化轨道的对称性,进而影响p_z轨道与氢的成键.本研究在一定程度上揭示了单层无序碳材料结构-性能的构效关系,为实验上设计特定性能的无序碳功能材料提供理论指导.

First-principles study on the electronic structure and hydrogen-adsorption properties of amorphous carbon monolayers

First-principles calculations were performed to systematically study the electronic structure and hydrogen evolution properties of the amorphous carbon monolayers. Our results show that the C-C bonds in the disordered structure undergo different degrees of stretching or compression, in the range of 26.7%, comparing to a pristine graphene. The atomic charge of C atoms changed in the range of -0.17~+0.16 electrons, resulting in electron localization on some C atoms. The localization of electrons enhances the chemical activity of the C atoms and hence the adsorption to alien atoms. The bonding of H atom with C, and the hydrogen evolution performance was found to be correlated with the bond angles of the C atoms. For a triple-coordinate carbon atom, three valence electrons combine strongly with the nearest carbon atom through the sp2 hybridization and the remaining pz orbital electron being unbonded. This electron could bond with adsorbates with relatively weak bonding. We found that the adsorption strength of this bond could be modified by tuning the angles of C-C bonds. Our results could provide deep insight into the correlation of structures and properties of amorphous carbon monolayer.