Water Splitting on TiO2-Based Electrochemical Cells: A Small Cluster Study

The water-splitting process on electrochemical cells is studied with focus on the energetics of the oxygen evolution reaction at the TiO 2 -based anodes. New reaction mechanisms are proposed that lead to the decomposition of water molecules on TiO 2 clusters. The oxygen evolution reaction at the anode is investigated using electronic structure calculations based on density functional theory (DFT). Simulations are carried out for different cluster sizes (monomers and dimers). For each reaction path, the free energy profile is computed, at different biases, from the DFT energies as well as the entropic and the zero-point energy contributions. The mechanisms of the oxygen evolution reaction explored in the present work are found to be energetically more feasible than alternative reaction pathways considered in previous theoretical works based on cluster approximations of the surface of the photocatalyst. Finally, the representation of the surface of specific, commonly occurring, titanium dioxide crystals (e.g., rutile and anatase) within the small cluster approximation is able to reproduce qualitatively the rutile (110) outperforming of the anatase (001) surface.