Interfacial Effects on the Band Edges of Ta3N5 Photoanodes in an Aqueous Environment: A Theoretical View

Summary Ta 3 N 5 , as a fascinating photoanode for solar hydrogen production, is expected to split water without any bias, because its band edge potentials straddle H 2 O redox potentials. Unfortunately, Ta 3 N 5 photoanodes can split water only when a bias of at least 0.6–0.9 V is applied. It means that they exhibit an onset potential as high as 0.6–0.9 V RHE (reversible hydrogen electrode). In this study, density functional theory calculations show that the band edge potentials of Ta 3 N 5 have a shift of approximately −0.42 eV relative to vacuum level when exposed to water. The increased ratio of dissociated water at Ta 3 N 5 -water interface will further make the band edge potentials shift −0.85 eV relative to vacuum level, implying the anodic shifts of the onset potential for water oxidation. The findings may reveal the mystery of the unexpectedly high onset potential of Ta 3 N 5 , as high as 0.6–0.9 V RHE .