Defect dipoles and stable dielectric properties improve Nb-doped Ba0.7Sr0.3TiO3 photocatalytic H2 evolution activity

Abstract

To enhance the photocatalytic hydrogen evolution reaction (HER) activity and stability of barium–strontium–titanate (Ba_0.7Sr_0.3TiO₃, BST), niobium (Nb⁵⁺) donor doped BST (Ba_0.7Sr_0.3Ti_1−xNb_xO₃) photocatalysts were synthesized via a sol–gel assisted solid phase method. It was found that the introduction of Nb⁵⁺ expands the lattice and impedes grain growth. In the mechanism of enhancing photocatalytic performance, on one hand, the doped Nb⁵⁺ ions generate two types of defects in the lattice of BST, which form defect dipoles to impede electron–hole recombination and improve the stability of photocatalytic performance. On the other hand, the temperature stability test of the dielectric constant shows that appropriate doping of Nb⁵⁺ ions will enhance the stability of carrier concentration in BST, thereby exhibiting superior HER activity. In terms of band structure, experiments and Density Functional Theory (DFT) confirmed that the doping of trace amounts of Nb⁵⁺ has a very weak influence on the band structure. Additionally, the photocatalytic hydrogen evolution of 1% Nb doped Ba_0.7Sr_0.3TiO₃ was 16.2% higher than that of Ba_0.7Sr_0.3TiO₃.