利用釩酸鉍光陽極將苯甲醇以光電化學形式氧化為苯甲醛

Abstract

近年來，光電催化（photoelectrocatalysis, PEC）領域已被廣泛應用於有機分子的氧化，相較於電催化，結合了光子能量能夠提供更節能的合成方法。光電化學反應中的半導體/電解質界面為非勻相催化中的產物選擇性提供了獨特的反應途徑。然而，儘管具有這些優勢──尤其是在有機溶劑中，對表面中間產物和效率損失途徑的全面理解仍然不足。在本論文中，我們深入研究了釩酸鉍（bismuth vanadate, BiVO4）光陽極在乙腈中，以不同的氧化還原介導劑，間接氧化苯甲醇為苯甲醛的光電性能。我們的研究揭示了光化學轉換速率受限的現象，歸因於有害表面態的形成，導致光生載子嚴重複合或氧化還原介導劑無法完全再生。基於先前研究強調在水性介質中的析氧反應，我們假設在BiVO4中引入鉬（molybdenum, Mo）摻雜可以調節表面態的密度。我們的實驗努力取得了顯著的成果，實現了近乎100％的法拉第效率和約18.0 μmol/cm2⋅h的轉化率。值得注意的是，這是目前為止使用光電催化方法合成苯甲醛的最高產率與法拉第效率，凸顯了其作為光驅動有機分子轉化之半導體材料的強大潛力。

In recent years, photoelectrochemical (PEC) cells have been widely employed for oxidizing organic molecules, offering a more energy-efficient alternative compared to electrocatalysis by harnessing photon energy. The semiconductor-electrolyte junction in PEC cells provides a unique avenue for product selectivity in heterogeneous catalysis. However, despite these advantages, a comprehensive understanding of surface intermediates and efficiency loss pathways, especially in organic solvents, is still lacking. Herein, we delved into the performance of bismuth vanadate (BiVO4) photoanodes in the indirect oxidation of benzyl alcohol to benzaldehyde in acetonitrile, using various redox mediators. Our investigations revealed a constraint on the light-to-chemical conversion rate, attributed to the formation of detrimental surface states, leading to serious recombination of photogenerated carriers and incomplete regeneration of redox mediator. Building upon prior research highlighting oxygen-evolution reactions in aqueous mediums, we hypothesized that the introduction of molybdenum (Mo) doping into BiVO4 could tune the density of surface states. Our experimental efforts yielded remarkable results, achieving close to 100% Faradaic efficiency and a conversion rate of ~18.0 μmol/cm2⋅h. Notably, this represents the highest yield and Faradaic efficiency for the synthesis of benzaldehyde using the PEC method to date, showcasing the potential of BiVO4 photoanodes as a promising candidate for light-driven organic transformation processes.