Using adatoms to tune the band structures of Cu2O surfaces for photocatalytic applications

Cuprous oxide (Cu2O) is a highly promising semiconductor with exceptional visible-light photocatalytic activity, and its nanoparticles have significant implications for promoting the Net Zero and Green Energy Economy due to low cost, ease of synthesis, and impressive performance. However, the photocatalytic effectiveness of Cu2O is heavily determined by the adsorbed species and crystal facets, both of which are crucial to the facet engineering of Cu2O. Here we applied first-principles calculations to investigate the geometric and electronic structures, as well as the thermodynamic stabilities, of Cu2O (100), (110), and (111) surfaces upon decoration with H, OH, Na, Cl, and Br units, respectively. We find that H, OH, and halogen atoms are efficient in stabilizing the Cu2O surface. The H atom is an excellent donor regardless of the surface orientation, whereas the roles of Br and Cl atoms as either donors or acceptors depend on specific surface conditions. Notably, the coverage conditions are essential in shaping the electronic properties of the (110) surface, on which the half-coverage OH-terminated surface manifests a suitable band structure facilitating the separation of the electron/hole pairs, thereby enhancing the photocatalytic efficiency. Accordingly, our calculations confirm that these species usually within the synthesis environment also have the ability to engage in the reaction and significantly alter the inherent facet-dependence of electronic structures in Cu2O crystals. These findings can help to elucidate various experimental results observed in Cu2O photocatalysis and can serve as an efficient strategy benefitting photocatalyst design.