Electron competitive migration regulating for dual maxima of water photolysis

Abstract

Electron competitive migration between the conduction band and charge trap centre is the key in governing the catalytic activity and the relevant applications of semiconductor nanomaterials, which is however poorly understood yet. Herein, we systematically studied the electron competitive migration in defective SnO₂ nanoparticles through hybridizing with a polymer electron donor, graphitic carbon nitride (g-C₃N₄). When varying the mass ratio of defective SnO₂ from 5% to 70%, an increase of surface-charge trapping centres (oxygen vacancies) in SnO₂ effectively regulated the electron competitive migration. As a consequence, dual catalytic activity maxima were observed in hydrogen generation from water splitting under visible light irradiation (λ > 420 nm). For instance, the relative mass ratios at 10% and 40% yielded maximum hydrogen generation rates of 54.3 μmol h⁻¹ g⁻¹ and 44.3 μmol h⁻¹ g⁻¹, respectively, far beyond that of 27.9 μmol h⁻¹ g⁻¹ for pure g-C₃N₄. Strikingly, the photon–hydrogen conversion efficiency also showed dual maxima values as SnO₂ mass ratio changes. These abnormal observations were comparatively investigated via XPS, EPR and photoluminescence spectra in solid state and aqueous environments. It is demonstrated that electron competitive migration was primarily caused by oxygen vacancies on the SnO₂ surface, which plays a key role in creating the dual catalytic activity maxima in water splitting.