Enhancing BiVO4 photoanode performance by insertion of an epitaxial BiFeO3 ferroelectric layer

BiVO₄ (BVO) is a promising material as the photoanode for use in photoelectrochemical applications. However, the high charge recombination and slow charge transfer of the BVO have been obstacles to achieving satisfactory photoelectrochemical performance. To address this, various modifications have been attempted, including the use of ferroelectric materials. Ferroelectric materials can form a permanent polarization within the layer, enhancing the separation and transport of photo-excited electron-hole pairs. In this study, we propose a novel approach by depositing an epitaxial BiFeO₃ (BFO) thin film underneath the BVO thin film (BVO/BFO) to harness the ferroelectric property of BFO. The self-polarization of the inserted BFO thin film simultaneously functions as a buffer layer to enhance charge transport and a hole-blocking layer to reduce charge recombination. As a result, the BVO/BFO photoanodes showed more than 3.5 times higher photocurrent density (0.65 mA cm⁻²) at 1.23 V_RHE under the illumination compared to the bare BVO photoanodes (0.18 mA cm⁻²), which is consistent with the increase of the applied bias photon-to-current conversion efficiencies (ABPE) and the result of electrochemical impedance spectroscopy (EIS) analysis. These results can be attributed to the self-polarization exhibited by the inserted BFO thin film, which promoted the charge separation and transfer efficiency of the BVO photoanodes.