Pulsed Laser Deposition of Ferroelectric SrTiO3 Shells Enables Polarization-Controlled Charge Separation in TiO2 Photoanode
Ferroelectric polarization offers a powerful route to govern the interfacial charge separation in photoelectrodes; however, chemically converted ferroelectric shells lack sub-nanometer thickness control, coherent strain retention, and chemically clean interfaces. Here, we use pulsed laser deposition to fabricate stoichiometric SrTiO3 shells on hydrothermally grown TiO2 nanorod arrays, achieving atomically defined core-shell architectures while preserving the one-dimensional transport geometry. The photocurrent density followed a volcano-shaped dependence on shell thickness and reached 1.9 mA cm-2 at 1.23 V versus RHE under AM 1.5G illumination for the optimized 15-mins sample, exceeding the established hydrothermal benchmark. High-resolution transmission electron microscopy and X-ray photoelectron spectroscopy revealed a tetragonally distorted, oxygen-stoichiometric shell, identifying coherent interfacial strain rather than defect dipoles as the origin of the ferroelectric order. Kelvin probe force microscopy directly imaged a polarization-induced built-in electric field whose magnitude scaled with charge-transfer efficiency and photocurrent density. Together, these complementary structural, chemical, electrostatic, and device-level measurements established a quantitative strain-polarization-built-in field-charge separation relationship. This work transforms ferroelectric photoanode engineering from empirical optimization into an atomically controllable and predictive materials strategy for high-efficiency solar water-splitting devices. This approach is readily extendable to visible-light absorbers and complex ferroelectric heterostructures.