Study of the modes of adsorption and electronic structure of hydrogen peroxide and ethanol over TiO_2 rutile (110) surface within the context of water splitting

摘要

Highlights•Geometric and electronic structure of H2O2adsorbed on TiO2(110) are studied computationally.•Its adsorption energy (fully dissociated) of 0.95 eV is comparable to that of ethanol.•The (-) changes in the work function are highest for molecular adsorption and lowest for the fully dissociated mode.•DOS indicated that the H2O2HOMO level is not overlapping with O3catoms of TiO2surface.AbstractWhile photocatalytic water splitting over many materials is favourable thermodynamically the kinetic of the reaction is very slow. One of the proposed reasons linked to the slow oxidation reaction rate is H2O2formation as a reaction intermediate. Using Density Functional Theory (DFT) H2O2is investigated on TiO2rutile (110) surface to determine its most stable adsorption modes: molecular, (H)O(H)O − (a), partially dissociated, (H)OO − (a), and fully dissociated (a) − OO − (a). We then compare H2O2interaction to that of a fast hole scavenger molecule, ethanol. Geometry, electronic structure, charge density difference and work function determination of both adsorbates are presented and compared using DFT with different functionals (PBE, PBE-D, PBE-U, and HSE + D). H2O2is found to be strongly adsorbed on TiO2rutile (110) surface with adsorption energies reaching 0.95 eV, comparable to that of ethanol (0.89 eV); using GGA PBE. The negative changes in the work function upon adsorption were found to be highest for molecular adsorption ( − 1.23 eV) and lowest for the fully dissociated mode ( − 0.54 eV) of H2O2. This may indicate that electrons flow from the surface to the adsorbate in order to make O(s)-H partially offset the overall magnitude of the oxygen lone pair interaction (of H2O2) with Ti4+cations. Examination of the electronic structure through density of states (DOS) at the PBE level of computation, indicates that the H2O2highest occupied molecular orbital (HOMO) level is not overlapping with oxygen atoms of TiO2surface at any of its adsorption modes and at any of the computation methods. Some overlap is seen using the HSE + D computational method. On the other hand the dissociated mode of ethanol (ethoxides) does overlap with all computational methods used. The high adsorption energy and the absence of overlapping of the HOMO level of H2O2with TiO2rutile (110) surface may explain why water splitting is slow.