First-principles study on surface chemistry of nanomaterials for energy conversion

Abstract

In this dissertation, we studied the surface chemistry of nanomaterial in energy conversion by performing the first-principles density functional theory simulation. The surface properties of the colloidal quantum dot which is the 3rd generation photovoltaic material have to be understood for the better efficiency of solar cells. The tetrapod-shaped InP nanocrystals consist of four arms covered with stable (110) surfaces along the (1 ̅1 ̅1 ̅) direction. By co-passivation of halide and amine ligands, the (111) surfaces are strongly stabilized and the tetrahedron-shaped InP nanocrystals are produced. By ligand coordination, the (111) surfaces of InAs NCs show the largest shift of the energy level compared to other facets because the ligands bind to the surface vertically. Among various ligands, chlorine atomic ligand capped (111) surfaces of InAs have the deepest energy level thanks to their high induced dipole moment. The difference between cubic and rhombohedral structures of AgSbS2 semiconductors is explored to further analyze the surface properties of AgSbS2 colloidal quantum dots. The fundamental physical properties of Ⅰ-Ⅴ-Ⅵ2 ternary semiconductors are systematically studied and suggest a promising candidate for solar cells. Also, the catalytic reaction in fuel cells or metal-air batteries occurs at the surface of the catalyst. Understanding the surface configuration has to be precedented for improving the stability and catalytic activity of the catalyst. The Co(II)(salen) molecules coordinated to the edge pyridinic N site of carbon materials show stability with a larger metal binding energy than cohesive energy and superior catalytic activity of oxygen reduction reaction. As the amount of N atoms increases, the binding energy of Ni atoms in Ni@Ni-NC increases and is larger than cohesive energy. The Ni/CxN4 shows better activity for oxygen evolution reaction than the hcp Ni (111) surface indicating the critical role of the shell in Ni@Ni-NC.