Single Atoms, Molecules, and Sub-Nanometer Sized Metals on Cadmium Sulfide Surfaces: A Density Functional Theory Investigation

One of the ways to address the increasing energy challenges of the world is through innovation at the materials-level, which requires a nanoscale understanding of new materials and their novel heterostructure designs. The main subject of study in this Thesis are the interfaces formed in the CdS-based nanoheterostructures. These nanoheterostructures are suitable for photocatalytic cleaving of water molecules, whereby hydrogen gas is generated, through the hydrogen reduction reaction. This, being a relatively cheap and renewable approach to generate the hydrogen fuel, is one of the promising pathways to address the energy challenges. The Thesis investigates two important interfaces of the CdS-nanoheterostructures which are expected to affect the turnover of the photocatalytic process, viz., the CdS-water (molecule) interface and CdS-metal interfaces. With the aim of gaining a first-principles understanding of these interfaces, we atomistically model them using density functional theory (DFT) based total-energy calculations. We studied these interfaces for a variety of monovacancies to reveal the CdS-water (molecule) interaction, whereas for CdS-metal interaction, we investigated the interfaces ranging from single metal atom to sub-nanometer clusters and to their extended epitaxial interfaces. The thesis identifies some important surface motifs like locally magnetic vacancies and interesting surface interactions like Ni-Cd bonding in studying these interfaces. The structural and chemical features that are characterized in the thesis should further be probed to determine their thermodynamic and kinetic effects on the catalytic pathways leading to hydrogen production.