Influence of Adsorbed Water on the Oxygen Evolution Reaction on Oxides

We study the interface between adsorbed water and stoichiometric, defect-free (110) rutile oxide surfaces of TiO2, RuO2, and IrO2 in order to understand how water influences the stabilities of the intermediates of the oxygen evolution reaction (OER). In our model the water is treated as explicitly adsorbed H2O molecules, which are found to form two-dimensional water chains (layers) on all investigated oxide surfaces.

The first chain formed by the most strongly bound H2O molecules is adsorbed on the 5-fold coordinated surface metal atoms. The second chain is composed of less strongly bound H2O molecules binding to bridging oxygens. The third chain interacts weakly and predominantly with the H2O molecules of the second layer, resembling bulk water.

We find that the stability of the water layer close to the oxide surface is almost the same as the one found on flat metal surfaces, such as the Pt(111) surface, despite the highly different adsorption pattern of the water molecules. We show that the presence of a water network has some effect on the interaction of individual intermediates of the OER with the oxide surface.

However, the theoretical OER overpotential remains almost unchanged in the case of RuO2 and IrO2, while it is increased by similar to 0.4 eV for TiO2.