鐵電性鐵酸鉍層對釩酸鉍光陽極催化水分解之影響

Abstract

光電化學水分解是一個熱門的研究領域，用於綠色能源的生成和儲存。儘管過渡金屬氧化物具有良好的操作穩定性，但這些材料的載子遷移率低、復合速率高，導致入射光子到電流的效率低，限制了商業化的潛力。在可用的光吸收材料中，釩酸鉍（BiVO4，簡稱BVO）是最適合光電化學水氧化反應的金屬氧化物光陽極。本研究旨在通過於氟摻雜二氧化錫（FTO）基板與BVO薄膜之間或上方沉積一層鐵電性鐵酸鉍（BiFeO3，簡稱BFO）層來增強BVO的載子傳輸效率。通過對鐵電性BFO層進行電晕極化形成能帶彎曲，於BVO/BFO界面處產生強電場來協助分離BVO層中的光生電子-電洞對。藉著使用線性掃描伏安法來評估光電化學效率的提高；然後應用電化學阻抗譜（EIS）和強度調變光電流/電壓譜（IMPS/IMVS）來解析BVO和BVO/BFO複合材料的傳輸和復合時間常數、擴散係數和衰減長度。在無外加偏壓的情況下，進行瞬態吸收(TAS)光譜測量，以獲得不同極化方向的BFO/FTO的載子動力學。研究發現，BFO的自發極化不僅可以改善BVO中的載子分離，還能在BFO本身中顯著改變載子動力學。總體而言，本研究證明，BFO鐵電性所造成之能帶彎曲可以有效改變BVO中的載子動力學。然而，BFO內的載子傳輸特性主導了此異質接面電極的光子到電流轉換效率。

Photoelectrochemical water splitting has been a vigorous field of research for the generation and storage of green energy. Although transition metal oxides exhibit decent operational stability, these materials also suffer from low carrier mobilities and high recombination rates, leading to low incident photon-to-current efficiencies and limited commercialization potential. Among the available light absorbers, bismuth vanadate (BiVO4, BVO) represents the best-performing metal oxide photoanode for PEC oxygen evolution reaction. This research aims to enhance the carrier transport efficiency of BVO by inserting a bismuth ferrite (BiFeO3, BFO) layer between or above a BVO thin film deposited on fluorine-doped tin oxide (FTO) substrate. Corona polling was performed to induce spontaneous polarization of the multiferroic BFO layer, with the aim of using the strong electric field at the BVO/BFO interface to assist the separation of photogenerated electron-hole pairs in the BVO layer. The enhancement in PEC efficiency was evaluated by linear sweep voltammetry; electrochemical impedance spectroscopy (EIS) and intensity modulated photocurrent/voltage spectroscopy (IMPS/IMVS) were then applied to deconvolute transport and recombination time constants, diffusion coefficients, and decay lengths for BVO, BFO, and BVO/BFO composite. Transient absorption spectroscopy (TAS) was conducted to obtain carrier dynamics of BFO/FTO with different polarization orientations in the absence of external bias. It was found that the spontaneous polarization of BFO can not only improve the carrier separation in BVO but also largely modifies the carrier dynamics within BFO itself. Overall, this work demonstrates that the ferroelectric band bending of BFO can efficiently alter the charge dynamics in the BVO. However, the carrier transport within BFO played a dominant role in affecting the photon-to-current conversion efficiency of the heterojunction electrode.