Understanding the Influence of Cation Doping on the Surface Chemistry of NaTaO₃ from First Principles

Sodium tantalate, NaTaO₃, has attracted interest as one of the few photocatalysts capable to perform overall water splitting, that is, simultaneously produce oxygen and hydrogen from water. In particular, an interesting and not fully understood observation is that the efficiency of NaTaO₃ increases dramatically in the presence of cation doping. To obtain better insight into the origin of this effect, we use first-principles calculations to investigate the fundamental structural, electronical, and chemical properties of pristine and Sr-doped NaTaO₃, a system for which several experimental studies have recently become available. Our results show that Sr donor-acceptor codoping at Na and Ta sites significantly reduces the formation energy of the Sr dopants. Further study of the energetics of the oxygen evolution reaction (OER) shows a substantial reduction of the OER overpotential for the codoped material, consistent with recent suggestions that codoping is crucial for increasing NaTaO₃'s efficiency.