溶液法製備磊晶釩酸鉍薄膜: 合成、鑑定與催化性能研究

Abstract

釩酸鉍（BiVO4）是一種具潛力應用於光電催化（photoelectrocatalytic, PEC）水分解與氧化反應的光陽極材料。然而，受限於真空製程的複雜性，其晶面依賴性催化行為尚未獲得充分研究。為克服此限制，本研究開發了一種結合金屬有機分解法（metal-organic decomposition, MOD）和快速熱退火（rapid thermal annealing, RTA）的溶液製程，用以合成BiVO4磊晶薄膜。此製程促進了奧斯特瓦爾德熟成（Ostwald ripening）並有效抑制了高溫下釩的損失。藉由優化熱處理條件，我們成功透過此方法在單晶YSZ和SrTiO3基板上生長出BiVO4 (001) 與 BiVO4 (010) 磊晶薄膜，並透過 X-ray 繞射與電子顯微鏡技術建立其磊晶成長機制。該溶液法製程克服真空法中常見的島狀生長問題，並獲得結構均勻、緻密且表面粗糙度低的薄膜。在光催化測試中，BiVO4 (010) 薄膜在羅丹明B降解中表現出相較於 (001) 晶面高約50%的反應效率，顯示其優異的晶面反應性。為進一步實現光陽極整合，本研究引入了氧化銦錫（indium tin oxide, ITO）作為導電背電極。儘管高溫退火有助於提高ITO的結晶性和導電性，但同時也使表面粗化，不利於後續BiVO4的生長。藉由在氬氣氛下進行後退火處理，可兼顧表面平整度並提升導電性。最終製備之 BiVO4 (001) /ITO/YSZ 光陽極在含有0.5 M Na2SO3的磷酸鹽緩衝液中展現出2.20 mA cm⁻2光電流密度，起始光電位約為 0.3 V (vs. RHE)。與對應多晶薄膜相比，具 (001) 晶向的 BiVO4 顯示出顯著提升的 PEC 效能，歸因於其增強的方向性電荷分離效率與表面復合抑制。阻抗分析亦顯示，特定晶向可有效促進界面電荷轉移。本研究展現了溶液法製備具生長取向氧化物磊晶薄膜的可行性，並有助於設計更高效的光電化學能量轉換裝置。

Bismuth vanadate (BiVO4) is a promising photoanode for photoelectrocatalytic (PEC) water splitting and oxidation, but its facet-dependent catalytic behavior remains underexplored due to reliance on complex vacuum-based fabrication. To address this, we developed a solution-based method combining metal–organic decomposition (MOD) and rapid thermal annealing (RTA) to grow epitaxial BiVO4 thin films. This process promotes Ostwald ripening and minimizes vanadium loss at elevated temperatures. Using this method, we successfully grew BiVO4(001) and (010) epitaxial films on single-crystal YSZ and SrTiO3 substrates, respectively. Through optimization of annealing conditions and structural analysis via XRD and electron microscopy, we established a model for solution-derived epitaxial growth, overcoming the island growth commonly observed in vacuum-based methods and yielding films with high structural uniformity, compactness, and low surface roughness. In photocatalytic testing, BiVO4(010) films exhibited approximately 50% higher activity than the (001) film in Rhodamine B degradation, indicating superior visible light absorption and surface reactivity. To realize photoanode integration, indium tin oxide (ITO) was introduced as a conductive back contact. Although high-temperature annealing enhanced ITO crystallinity and conductivity, it also deteriorated surface morphology, impeding epitaxial BiVO4 growth. A post-annealing step in an argon atmosphere was thus employed to improve conductivity while preserving surface flatness. The resulting BiVO4(001)/ITO/YSZ photoanodes delivered a photocurrent of 2.20 mA cm⁻2 and an onset potential of 0.3 V vs. RHE in phosphate buffer with 0.5 M Na2SO3 sacrificial hole scavenger. Compared to polycrystalline films, (001)-oriented BiVO4 showed enhanced PEC performance, attributed to enhanced directional charge separation and suppressed surface recombination. Impedance analysis further confirmed that specific crystallographic orientations enhance interfacial charge transfer. This study demonstrates the feasibility of using a solution-based approach to control the crystallographic orientation of oxide epitaxial thin films and contributes to the design of more efficient photoelectrochemical energy conversion devices.