Activation of barium titanate for photocatalytic overall water splitting via low-valence cation codoping

Abstract

Barium titanate (BaTiO₃) has long been regarded as inactive for photocatalytic overall water splitting, in stark contrast to its perovskite counterparts SrTiO₃ and CaTiO₃. Here we report that BaTiO₃ codoped with Al³⁺ and Sc³⁺ at Ti⁴⁺ sites under flux synthesis conditions is activated as a robust photocatalyst for overall water splitting. This material achieves apparent quantum yields of 29.8% at 310 nm and 27.5% at 365 nm, representing the first demonstration of efficient overall water splitting on BaTiO₃. Comparative analyses show that BaTiO₃ doped only with Al³⁺ suffers from severe band-edge disorder, whereas BaTiO₃ codoped with Al³⁺ and Mg²⁺ exhibits clear activation with moderate efficiency. In contrast, BaTiO₃ codoped with Al³⁺ and Sc³⁺ achieves the critical defect and structural control required to push the material across the threshold from inactive to highly active. These findings overturn the long-standing perception of BaTiO₃ as unsuitable for water splitting and establish a general design principle for activating previously inactive perovskite oxides, thereby expanding the materials palette for solar-to-hydrogen energy conversion.