Mixed NaNbxTa1−xO3 perovskites as photocatalysts for H2 production

Abstract

Mixed perovskites NaNb_xTa_1−xO₃ were prepared by solid state reaction (SSR) as well as by hydrothermal (Hyd) methods, and their photocatalytic activity for hydrogen production was studied using the water–methanol system. The assessment of the NaNb_xTa_1−xO₃ materials obtained by the SSR method reveals that the activity of the individual NaTaO₃ and NaNbO₃ perovskite semiconductors is largely improved in their combined form. Among several compositions employed, the 1 : 1 molar ratio (NaNb_0.5Ta_0.5O₃ sample) shows the best performance for H₂ production. On the other hand, using the Hyd method, which implies lower synthesis temperature, the photocatalytic activity of NaNb_0.5Ta_0.5O₃ is enhanced compared to the material obtained by the high temperature SSR method. The characterization of the materials reveals that catalyst properties like high surface area, a larger proportion of the monoclinic crystalline phase and lower crystal defects for the NaNb_0.5Ta_0.5O₃ photocatalyst synthesized by the hydrothermal route may be responsible for its superior activity. Further significant improvement in the activity of the NaNb_0.5Ta_0.5O₃ semiconductor is achieved by the addition of Pt as the co-catalyst, showing that the loading amount has a great influence on the activity. The highest H₂ production rate (37.8 μmol g⁻¹ min⁻¹) is obtained for the catalyst prepared by the hydrothermal method (Hyd-NaNb_0.5Ta_0.5O₃) with 0.125 wt% of Pt loading. Moreover, the developed Hyd-NaNb_0.5Ta_0.5O₃ sample shows a stable H₂ evolution activity for several reuse cycles.