利用小訊號微擾技術解析釩酸鉍光陽極在光電催化水分解中的表面電荷載子動力學

Abstract

單斜白鎢礦結構BiVO4 (ms-BiVO4) 具有間接能隙 (~2.4 eV) 的特性、適合的能帶位置，以及在廣泛工作條件下穩定的電化學性能，是一種很有前景的半導體光陽極，適用於高效光電化學(photoelectrochemical, PEC) 水分解。儘管具有優越的特性，ms-BiVO4 仍受到極化子躍遷導致的低電子遷移率，以及由於表面復合和光降解而導致的異質半導體-電解質界面 (semiconductor-electrolyte interface) 的電荷轉移動力學降低的影響。通過簡便的溶膠-凝膠製備方法，我們合成了沉積在FTO 基板上的多晶ms-BiVO4 光陽極，重點分析了光陽極界面上普遍存在的本徵表面缺陷態的作用。此外，採用基於PEC 的小擾動探測技術，通過分析不同濃度電洞清除劑的影響和使用不同電解質的效果，來解析各種實驗條件下不同的載流子動力學。因此，我們觀察到ms-BiVO4光陽極在陽極掃描過程中逐漸表現出多種主導現象，包括體相擴散/復合、表面陷阱/去陷阱和費米能階釘扎 (Fermi-level pinning)，每種現象都與其使用小擾動技術得到的獨特光譜特徵和趨勢相關。總結而言，我們定性地假設ms-BiVO4光陽極存在兩種不同的本徵表面態，這些表面態深刻影響界面能量學以及整體析氧反應(OER) 過程。

Monoclinic scheelite BiVO4 (ms-BiVO4), with a mainly indirect bandgap (~2.4 eV) character, suitable band position, and stable electrochemical performance within a wide range of working conditions, serve as a promising semiconductor photoanode for efficient photoelectrochemical (PEC) water splitting. Despite its superior features, ms-BiVO4 suffers from low electron mobility due to polaron hopping and reduced charge transfer kinetics at the heterogeneous semiconductor-electrolyte interface (SEI) due to surface recombination and photodegradation. Through facile sol-gel based fabrication method, we synthesis polycrystalline ms-BiVO4 photoanode deposited on FTO substrate, where we focus on analyzing the role of intrinsic surface defect states (i-SS) commonly exist on the photoanode interface. Furthermore, PEC-based small perturbation probing techniques were employed to deconvolute distinct carrier dynamics along various experimental conditions, through analyzing the impact of different concentration of hole scavenger and the usage of different electrolyte. Consequently, we observed that ms-BiVO4 photoanode gradually exhibit multiple dominating phenomenon during anodic scanning, which includes bulk diffusion/recombination, surface trapping/de-trapping and Fermi-level pinning (FLP), each associated with its unique spectral features and trends using small perturbation techniques. In conclusion, we qualitatively assumed that ms-BiVO4 photoanodes exhibit two distinctive intrinsic SS, which influence the interfacial energetics and thus the overall OER process profoundly.