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

Although SrNbO2N has a promising band gap of similar to 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. SrMgx/3Nb1-x/3O2+yN1-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 SrMg0.2Nb0.8O2+yN1-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.