DFT study for OH radical formation on SrTiO3(001) surface and the effect of Bi

Abstract

Density functional theory (DFT) calculations were performed in order to explore the hydroxyl radical (OH) formation on pristine and bismuth (Bi) deposited on the strontium titanate (SrTiO3) (001) surface. The hydroxyl radical formation may occur when water interacts with SrTiO3 surfaces. It has been reported in the literature an increase in the pH of aqueous solutions with SrTiO3:Bi powder under solar irradiation. This suggests that Bi incorporation into the SrTiO3 structure may help to increase OH concentration in the solution, this means an improvement in OH formation due to Bi. First, we have studied the water SrTiO3(001) interaction in different configurations and found that chemisorption process takes place. Configurations with larger adsorption energies were used as reactants, and then OH formation was proposed. The projected density of states (PDOS) per layer shows a reduction in the surface bandgap of 0.7 eV compared to the calculated bulk value of 1.6 eV. Charge density maps and isosurfaces show shared electronic charge density between the adsorbed species (water molecule, OH radical and hydrogen atom) and SrTiO3(001) surface, pristine and Bi deposited systems. Minimum energy pathway (MEP) calculated with nudged elastic band (NEB) method shows an improvement in OH formation on Bi deposited SrTiO3(001) due to a reduction in the activation energy. For the forward reaction, the activation energy on pristine SrTiO3(001) is 1.39 eV, 0.58 eV larger than the 0.81 eV needed when Bi is present.