Facet-Dependence of Electron Storage in Gold-Decorated Titania Nanocrystals

A variety of materials have been developed over the last two decades with the goal of extending the function of light-absorbing devices to low-light or nighttime conditions. Typically, this requires storage of photogenerated charges. The capacity of a material to store charges depends on a range of physicochemical features, including the crystallographic nature of materials' interfaces, which we investigate here. We implemented a model system consisting of gold nanoparticles (AuNPs) supported on titanium dioxide (TiO2) anatase nanocrystals with predominantly (101), (100), or (001) facets. Cyclic voltammetry in dark, anaerobic conditions showed that all three materials exhibited increased current densities with increasing illumination time, with the highest increase observed for Au/TiO2(001). We further employed photocharged Au/TiO2 particles for catalytic reactions in the dark and found a consistent trend of Au/TiO2(001) being the most active. Using density functional theory, we calculated the Bader charge and the partial density of states, revealing that the presence of additional oxygen atoms at the Au/TiO2 interface leads to charge depletion from Au, providing more accessible vacant states to accept electrons from TiO2, with calculations showing the greatest charge depletion for Au/TiO2(001). Our results suggest that crystal surface engineering can be used as a powerful tool to optimize materials for electron storage.