Defect engineering of two-dimensional Nb-based oxynitrides for visible-light-driven water splitting to produce H 2 and O 2 .

Two-dimensional (2D) Nb-based oxynitrides are promising visible-light-responsive photocatalysts for the water splitting reaction, but their photocatalytic activity is degraded by the formation of reduced Nb 5+ species and O 2- vacancies. To understand the influence of nitridation on the formation of crystal defects, this study synthesized a series of Nb-based oxynitrides through the nitridation of LaKNaNb 1- x Ta x O 5 ( x = 0, 0.2, 0.4, 0.6, 0.8, 1.0). During nitridation, K and Na species volatilized, which helped transform the exterior of LaKNaNb 1- x Ta x O 5 into a lattice-matched oxynitride shell. Ta inhibited defect formation, yielding Nb-based oxynitrides with a tunable bandgap between 1.77 and 2.12 eV, straddling the H 2 and O 2 evolution potentials. After loading with Rh and CoO x cocatalysts, these oxynitrides exhibited good photocatalytic activity for H 2 and O 2 evolution in visible light (650-750 nm). The nitrided LaKNaTaO 5 and LaKNaNb 0.8 Ta 0.2 O 5 delivered the maximum H 2 (19.37 μmol h -1 ) and O 2 (22.81 μmol h -1 ) evolution rates, respectively. This work provides a strategy for preparing oxynitrides with low defect densities and demonstrates the promising performance of Nb-based oxynitrides for water splitting.