Elucidating the Barriers on Direct Water Splitting: Key Role of Oxygen Vacancy Density and Coordination over PbTiO₃ and TiO₂

In this work, using the state-of-the-art first-principles calculations based on density functional theory, we found that concentration and coordination of surface oxygen vacancies with respect to each other were critical for direct water-splitting reaction (001) surfaces PbTiO3 TiO2. For happen TiO2-terminated surfaces, it is necessary have two neighboring O acting as active sites host adsorbing water molecules. However, eventual dissociation O–H bonds possible only in presence an additional nearest-neighbor vacancy. Unfortunately, third vacancy inhibits formation molecular hydrogen by trapping dissociated H atoms surfaces. Formation up three energetically less costly both terminations PbTiO3(001) compared those TiO2; Pb leads weaker over these Molecular more favorable PbO-terminated PbTiO3, requiring vacancies. molecule retained near weak van der Waals forces. Our study indicates barriers leading low productivity processes. First foremost, there entropic barrier imposed requirement at least vacancies, sterically hindering process. Furthermore, are also enthalpic or removal H2 molecules from surface. The dictating evolution consistent chemical intuition: nearest neighbor formed should be reduced enough inhibit spontaneous oxidation under ambient conditions.