Simulations of hydrogen on palladium loaded anatase surfaces from the view of photocatalytic hydrogen production by using VASP

Abstract

In this thesis we report of simulations that have been performed with CSC's Puhti supercomputer utilizing The Vienna Ab initio Simulation Package (VASP). The research subject has been the semiconductor anatase, a polymorph of titanium dioxide (titania), and its crystal surface plane (101) with palladium clusters on it. On the surface, adsorption energies of hydrogen atoms (H) and dimers (H2) are explored by varying the palladium cluster size (PdN) with N=1-5. It is found that N=2,3 gives the most stable hydrogen adsorption but the Pd-adsorption is the most unstable with them, while N=4,5 gives the most stable Pd-adsorption. Also, it is found that palladium effectively lowers the energy gap of anatase.

It is demonstrated that the lowered energy gap and stable hydrogen bonding are beneficial features of a material for photocatalytic hydrogen production, which might be an important source for clean energy in the future.

The thesis starts with relevant background physics and chemistry of the subject: some solid state physics; the density functional theory (DFT); computational methods including the exchange and correlation (XC) energy functional of Perdew, Burke, and Ernzerhof (PBE) and the projector augmented-wave method of Blöchl, Kresse, and Joubert (PAW); titania photocatalysis; and the structure and the properties of anatase and the (101) surface of it. Further the computational tools are introduced, namely, the VASP simulation package, the basic simulation procedure performed with it, and details of the Puhti supercomputer.