The Effects of Crystal Structure and Electronic Structure on Photocatalytic H₂ Evolution and CO₂ Reduction over Two Phases of Perovskite-Structured NaNbO₃

Cubic and orthorhombic NaNbO₃ were fabricated to study the effects of crystal structure and electronic structure on the photocatalytic activities in detail. The samples were characterized by X-ray diffraction, field emission transmission electron microscopy, high-resolution transmission electron microscopy, UV–visible absorption spectroscopy, and X-ray photoelectron spectroscopy. The photocatalytic activities of the two phases of NaNbO₃ have been assessed by H₂ evolution from aqueous methanol solution and CO₂ photoreduction in gas phase. The photocatalytic H₂ evolution and CO₂ reduction activities over cubic NaNbO₃ were nearly twice of those over orthorhombic NaNbO₃. The first-principles calculation reveals that the higher activity over cubic NaNbO₃ can be attributed to its unique electronic structure, which is beneficial for electron excitation and transfer.