Visible-light photocatalytic hydrogen production in a narrow-bandgap semiconducting La/Ni-modified KNbO₃ ferroelectric and further enhancement via high-field poling

Compared with traditional wide-bandgap oxide ferroelectrics that exhibit excellent UV photocatalysis, narrow-bandgap semiconducting ferroelectrics demonstrate broad application prospects in the field of visible-light photocatalysis. However, due to significant current leakage and weakening of ferroelectricity in most semiconducting ferroelectrics, establishing high-field poling via an external electric field to boost photocatalytic activity further is difficult. Therefore, balancing the semiconductivity and ferroelectricity of such materials is challenging. Here, a novel visible-light-driven semiconducting ferroelectric photocatalyst of La/Ni-modified KNbO₃, namely, (1 − x) KNbO₃-xLaNiO_3−δ with x = 0.00-0.04, is successfully prepared via sintering. Similar to traditional wide-bandgap KNbO₃ ferroelectrics, semiconducting ferroelectrics also manifest an excellent photocatalytic hydrogen evolution (PHE) rate under simulated sunlight (1169.7 µmol g⁻¹ h⁻¹). The 0.99KNbO₃-0.01LaNiO_3−δ composition can exhibit visible-light PHE activity (40.1 µmol g⁻¹ h⁻¹). Moreover, semiconducting ferroelectrics at room temperature can still be poled under a high external electric field, and the visible PHE rate of 0.99KNbO₃-0.01LaNiO_3−δ can be increased by 16 times (642.0 µmol g⁻¹ h⁻¹) via high-field poling. This remarkable visible PHE rate observed in the modified system is associated with the very narrow bandgap of 1.45-1.24 eV and the enhancement of carrier separation efficiency by high-field poling. This work provides a feasible solution for designing ferroelectric-based oxide photocatalysts with excellent visible-light activity and insights into the polarisation mechanisms of semiconducting ferroelectrics.