Ca2+ substitution induced phase coexistence and synergistic regulation of Ti3+ defects to improve piezoelectric–photocatalytic water splitting performance of BaTiO3

Abstract

The synergistic effect between piezoelectricity and photocatalysis opens a new pathway for efficient water-splitting hydrogen production. However, limitations such as low mechanical energy conversion efficiency and poor directional charge transfer hinder its practical application. In this study, a BaTiO₃-Ca_0.2 photoanode with a coexisting tetragonal–orthorhombic phase involving Ti³⁺ defects and lattice distortion defects was synthesized by incorporating Ca²⁺ into BaTiO₃. The results show that under ultrasonic treatment, the photocurrent density of BTO-Ca_0.2 at 1.23 V_RHE reaches 1.89 mA cm⁻², which is 3.63 times that of pristine BaTiO₃. DFT and experimental tests confirm that under ultrasonic treatment, the interface polarization gradient zone of the tetragonal–orthorhombic phase coexistence enhances the built-in piezoelectric field. Meanwhile, the modulation of the Ti³⁺ defect-induced orbital structure forms shallow energy levels, which improves charge separation and migration performance, accelerates the adsorption and dissociation of water molecules on the electrode surface, and leads to a comprehensive enhancement of piezoelectric–photocatalytic water splitting performance. These findings provide a feasible strategy for designing a high-performance piezo-photoelectric chemical (Piezo-PEC) efficient photoelectrode.