Water on manganese doped rutile TiO₂(110) surfaces

Abstract

Photocatalytic water splitting has been studied as a potential method for solving the energy supply and environmental issues related to the use of fossil fuels since it was first shown to be possible by Fujishima and Honda in 1972 using titanium dioxide as a catalyst. Titanium dioxide is still considered one of the best catalyst candidates due to its low cost, non-toxicity, and chemical stability. Unfortunately, titanium dioxide some issues limiting its usefulness in the photocatalytic water splitting process. One of the ways used to make it a more efficient catalyst is doping it with transition metals, which has been shown to allow titanium dioxide nanoparticles to absorb visible light and increase the photocatalytic activity on its surfaces.

The aim of this work is to use density functional theory based calculations with the projector augmented wave method to study the adsorption behavior of water on clean and manganese doped rutile titanium dioxide (110) surfaces. The activation barriers for the transitions from molecularly adsorbed to decomposed water are computed using the climbing image nudged elastic band method. Additionally, the rates of the transitions were estimated using harmonic transition state theory. It was found that doping the surface with manganese makes the adsorption energies larger in magnitude and decreases the energy difference between molecularly adsorbed and decomposed water. The activation barriers are lowered by roughly a third, and in the case of a sixfold coordinated manganese dopant, the transition becomes slightly endoergic. The transition rates are also increased by the doping. These results suggest that doping with manganese increases the ability of the rutile (110) surface to split water.