Promotion of photo-induced charge carrier separation in a heterostructure via introducing an enhanced polarization electric field

Abstract

Titanium dioxide (TiO2) has been well adopted as the photocatalyst which possesses the highest possibility for application. Its integration in photoelectrochemical (PEC) system would further benefit the practical application. The effective separation and utilization of photo-induced charge carriers are still the key to enhance the performance in a PEC water splitting system. A Au/BiFeO3/TiO2 ternary heterostructure with an enhanced polarization electric field was prepared by doping Ca and Cr ions in pure BiFeO3, which resulted in a 4.6-fold higher photocurrent density than that of the pure TiO2 photoanode for the oxygen evolution reaction (OER) at 1.23 V vs. RHE. We attributed this improvement to a synergistic effect of the ferroelectric polarization electric field and ternary heterostructure, which effectively promotes the separation and utilization of photo-induced charge carriers. In the Au/BiFeO3/TiO2 heterostructure, ferroelectric BiFeO3, especially Ca and Cr doped BiFeO3, can create an electric field with spontaneous polarization, and the as-formed built-in field at the interface provides a favorable channel for the separation of photo-induced electrons and holes. After poling with a relatively high electric field, the OER performance of the Au/Bi0.9Ca0.1Fe0.9Cr0.1O3/TiO2 photoanode can be further improved, which confirms the positive effect of the ferroelectric polarization electric field on promoting charge separation. This work extends the application of ferroelectric materials in the PEC research field and highlights the significant role of polarization electric fields in promoting PEC performance.