First-Principles Modeling of Dye Anchoring on (001) γ‑Monoclinic WO3 Surfaces: The Role of Oxygen Vacancies

Here, we focus on the dye’s anchoring mechanism onto the (001) monoclinic WO3 surface. We present first-principles simulations, based on density functional theory (DFT), to get atomistic insights into the adsorption of three different anchoring groups [benzoic acid (BA), Catechol (Cat), and phenylphosphonic acid (PA)] onto the clean and oxygen-defective (001) WO3 surfaces, considering implicit solvation effects and dispersion corrections. The results show that both BA and PA preferably adsorb in a molecular monodentate binding mode on the clean surface, while the presence of oxygen vacancies on the surface makes the dissociative bidentate bridging the preferred binding mode. In the case of the Cat molecule, two configurations were found to be close in energy in solution on clean surfaces, whereas the mono-deprotonated monodentate mode is the most stable one on defective surfaces. The presence of oxygen vacancies on the surface increases, in absolute value, the adsorption energies of the anchoring groups, without affecting their relative stability. The present results, providing for the first time atomic-scale details on the dye anchoring mechanism on monoclinic WO3 substates and indicating un unfavorable W–W distance pattern on the surface (001) for anchoring traditional carboxylic, phosphonic, and catechol anchoring groups, may suggest novel design rules for the optimization and the selection of alternative anchoring functionalities for WO3-based dye-sensitized solar cells and hybrid photocatalysts.