Defect management and efficient photocatalytic water oxidation reaction over Mg modified SrNbO2N

Abstract

Although SrNbO₂N has a promising band gap of ∼1.8 eV for solar water splitting, its photocatalytic activity is generally very poor under ordinary conditions, primarily due to high defect levels caused by synthetic procedures. In this work, we managed to control defect levels inside SrNbO₂N by incorporating Mg into the structure, i.e. SrMg_x/3Nb_1−x/3O_2+yN_1−y (0 ≤ x ≤ 1). Strikingly, a number of important properties such as band gap value, defect level, nitrogen content and particle size can be tuned by varying the amounts of Mg in the structure. More importantly, efficient photocatalytic water oxidation into oxygen was realized using these Mg modified SrNbO₂N. An apparent quantum efficiency (AQE) as high as 5.13% was reached at 420 ± 20 nm for SrMg_0.2Nb_0.8O_2+yN_1−y (x = 0.6), which stands as the highest AQE reported to date for SrNbO₂N. Mott–Schottky and X-ray photoelectron spectroscopy analyses revealed the shift of valence band maximum of SrNbO₂N in response to Mg uptake. Moreover, open-circuit voltage decay measurements confirmed a much prolonged charge lifetime in Mg modified SrNbO₂N. Thus, Mg serves not only to tailor band edge positions but also to ameliorate charge separation conditions in SrNbO₂N, both of which contribute to the superior photocatalytic activities.