First principles study of thermally activated processes on transition metal surfaces

Abstract

Thermally activated processes, such as ionic conductivity, viscosity, diffusion, and some chemical reactions, are the ones where the system undergoes a rare transition from one potential energy well to another. I will start my talk by introducing the theoretical framework I used to model these processes. In the next part, I will describe my first research project where I studied the oxidation process of the Ti(0001) surface, which is of great interest due to potential applications in jet engine design. I have investigated the effect of alloying Ti with different p and d block elements and their effect on the oxidation diffusion kinetics. From my calculations of diffusion barrier at different O coverages, I find that the higher electropositive an alloying element is compared to Ti the higher will be its capability to hinder the Ti oxidation. Our experimental collaborators are implementing these findings to design better oxidation resistant Ti alloys. In my second project, I studied the hydrogen purification process done using a PdCu permeation membrane and the application of sulphur impurities to enhance the process. From my study, I find that the dissociation process of H2S is an activated process on the PdCu(110) surface and there is a decrease in the adsorption energy of hydrogen in the vicinity of S adatoms. Temperature dependence study suggests that the rate associated with both these processes gets amplified at higher temperatures and hydrogen coverages. Also, the rate-limiting flux study suggests that the flux associated with penetration of hydrogen from surface to sub-surface is enhanced at high hydrogen coverages. These results can help us design better PdCu/S membranes for more efficient hydrogen purification.