A first-principles study of the electronic structure, surface stability, and band alignment of niobium pentoxide

Currently, there is a growing development to find new materials to achieve clean and sustainable energy production, and one of the key processes in this effort is to replace expensive noble element catalysts with less costly transition metal oxides. Niobium pentoxide (Nb₂O₅) is a wide-gap semiconductor with good catalytic properties which makes it an essential material in this kind of technological applications, however, there are no theoretical studies on the surface physical properties for the different phases of this compound. In this work, we have performed first-principles calculations to study the bulk electronic properties and the low-index non-polar surfaces of the B and R crystallographic phases of Nb₂O₅. We have used a semi-local exchange–correlation functional (PBEsol) along with the G_oW_o approximation to calculate their gap and band alignments with respect to the vacuum. It has been found that these phases are indirect wide-gap semiconductors, the calculated gaps for B (R) are E_g ^PBEsol=2.6eV (2.1 eV) and E_g ^G_oW_o =4.2eV (3.8 eV). On the other hand, it is established that the most stable surfaces are (010) and (001) for B and R, respectively, and their highest conduction band edges are along the (1̄01) and (100) terminations, both being above the CO₂/CH₂O₂ reduction potential at pH = 7. Our results present clues into utilizing these Nb₂O₅ phases on technological applications such as photocatalytic uses on water splitting and carbon dioxide reduction.