Crystalline phase-dependent photocatalytic water splitting for hydrogen generation on KNbO3 submicro-crystals

Potassium niobate (KNbO₃) submicro-crystals with cubic and orthorhombic phases were hydrothermally prepared and characterized by powder X-ray diffraction, micro-Raman spectroscopy, Fourier transform infrared spectroscopy, nitrogen adsorption–desorption, diffuse reflectance UV–visible spectroscopy, X-ray photoelectron spectroscopy, scanning electron microscopy, and high-resolution transmission electron microscopy. The photocatalytic performance of the as-prepared KNbO₃ samples was evaluated toward H₂ generation from an aqueous methanol solution under UV. The surface area-normalized rate of H₂ production over submicro-cubes with cubic phase is two times larger than that of submicro-rods with orthorhombic phase. In addition, both cubic and orthorhombic KNbO₃ submicro-crystals showed much higher reactivity than commercial KNbO₃ bulk-like powders. The underlying mechanism was discussed in terms of crystal structure and electronic structure. The results from this study are potentially applicable to a range of perovskites useful in water splitting as well as other areas of heterogeneous photocatalysis.