Effect of Bulk Hydrogen on the Photocatalytic Activity of Semiconducting Ta3N5: A Hybrid-DFT Viewpoint

Ta3N5 is a promising candidate for photocatalytic water splitting. Hydrogen impurities are always introduced into the Ta3N5 lattice during arnmonolysis of TaOx precursors. Limited attention has been paid to the effect of hydrogen impurities in Ta3N5 on photocatalytic water splitting. In this study, the feasible configurations of hydrogen impurities in Ta3N5 and their effect on Ta3N5-based photocatalytic water splitting are theoretically investigated. Hybrid-DFT (density functional theory) calculations for hydrogen-doped Ta3N5 show that hydrogen impurities are probably introduced into Ta3N5 as interstitial defects due to low formation energy of interstitial hydrogen-doped Ta3N5. Hydrogen in Ta3N5 leads to a significant positive shift (vs RHE) in the band edge positions of Ta3N5, which can undermine the energetics for water reduction and increase the onset potential for water oxidation. Hydrogen impurities also act as shallow level donors, which can compensate for acceptors and aggravate the band edge engineering to realize beneficial energetics for Ta3N5.