Coupled Ferroelectric–Photoelectrochemical in Water Reduction Over BiFeO3 Thin Film Heterostructure Modulated by Rare-Earth Doping

Abstract

Ferroelectric polarization plays a key role in tuning charge dynamics and surface stoichiometry in photoelectrochemical (PEC) water reduction. In this work, p-type ferroelectric BiFeO3 (BFO) thin film heterostructures are modified by rare-earth (RE) doping (Nd, Sm, and Gd) to explore their influence on electrical leakage, ferroelectric polarization, charge transfer efficiency, and PEC performance. The heteroepitaxial method is used to grow upward-polarized BFO (111) films doped with 7% Nd, 10% Sm, and 7% Gd. Among the RE-doped BFO, the 7% Gd-doped BFO (BGFO) particularly reveals a ∼12% decrease in oxygen vacancies (VO) compared to the BFO in X-ray photoelectron spectroscopy (XPS) O 1s examinations. The density functional theory (DFT) calculations further confirm the lowest defect of VO in the BGFO. Consequently, Gd doping is tremendously effective in reducing leakage current by ∼2-order, enhancing the subsequent remnant polarization from 33 µC cm−2 (BFO) to 83 µC cm−2 (BGFO). Meanwhile, an inhibited charge recombination in BGFO improves the lifetime of photoexcited charge carriers by ∼1.8-fold. These improvements collectively facilitate charge migration across the BGFO/electrolyte interface in PEC activities, resulting in a ∼2.8-fold increase in incident photon-to-current efficiency (IPCE) and a ∼1.5-fold enhancement in photogenerated charge transfer density.