Dependence on the structure and surface polarity of ZnS photocatalytic activities of water splitting: First-principles calculations

It has been reported that phase structure and surface polarity largely affect the photocatalytic efficiency of semiconductor nanostructures. To understand the chemical activity of ZnS at the electronic level, we investigate electron structures and carrier transportation ability for bulk intrinsic zinc blende (ZB) and wurtzite (WZ) ZnS, as well as the reaction pathway of hydrogen generation from water splitting on Zn- and S-terminated polar surfaces. The electron structure calculations prove that the WZ phase possesses a higher reducing ability than the ZB phase. The conductivity of the bulk ZB phase surpasses that of the WZ phase at or above room temperature. As the temperature increases, the asymptotic conductivity ratio of WZ/ZB is close to the Golden Ratio, 0.62. Reaction kinetics studies indicate that Zn-terminated polar surfaces are more chemically active than S-terminated polar surfaces in the reaction of hydrogen generation from water splitting. The calculation results suggest that the first H splitting from water on Zn-terminated polar surfaces can occur with ground state electronic structures, while photo-assistance is necessary for the first H splitting on the S-terminated surfaces. Electronic triplet states calculations further show that Zn-terminated surfaces are more photosensitive than S-terminated surfaces.