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

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.