| 摘要: | 光電化學系統（PEC）可以像自然界通過光合作用一樣直接利用半導體
電極中的光生電子-電動對來催化反應，若使用生物質當反應物進行選擇性氧化來生成高經濟價值的產物，將是一道對環境友善且節省能源的製程。我們 究 嘗 試 開 發 吸 收 可 見 光 的 光 陽 極 ， 並 應 用 在 5- 羥甲基糠醛 (5-hydroxymethylfurfural, HMF)的選擇性氧化上。本研究首先用旋轉塗佈法製備 BiVO4 薄膜光電極，並經由塗佈緩衝層、保護層和裝載共觸媒來提升光電極之性能。緩衝層改善了 BiVO4 表面的性質，使晶粒更為均一完整，在1.2 V vs. RHE 下，光電流密度提升 33%，且 IPCE 在波段 400 nm 時從 16%提升至 34%；NiOx 共觸媒的裝載提升了氧化動力，讓水解反應之起始電位往還原方向 0.2 V vs. RHE，但在高偏壓區的電流卻出現被抑制的情形，代表也存在界面與表面的問題需要克服；保護層 TiO2 的性質有類似透明導電氧化物(Transparent conductive oxide)的作用，能有效降低半導體與電解液界面之電子-電洞對再結合。而後我們選用光電流密度最高的 BiVO4/SnO2光電極在不同離子電解液與 pH 值環境下測試穩定性，發現在 pH=10 的硼酸鈉緩衝溶液有最好的表現性，並在此進行 HMF 之選擇性氧化反應。我們藉由 TEMPO 當反應媒介，成功轉化出產物 FDCA，在反應總載子數為 78 庫倫後，HMF 有 74%的轉化率，FFCA 與 FDCA 分別有 29%、30%的產率，40%、41%的選擇率，法拉第效率為 91%。而由濃度變化的計算，我們得出 HMF 為一級反應。;The photoelectrochemical (PEC) can directly utilize the photo-generatedelectron-hole pair in semiconductor electrode to catalyze the reaction like nature
through photosynthesis. If the biomass is used as the reactant for selectiveoxidation to generate a product of high economic value, it will be anenvironmentally friendly and energy-saving process. We tried to develop a
photoanode that absorbs visible light and applies it to the selective oxidation of 5-hydroxymethylfurfural (HMF). In this study, the BiVO4 thin film photoelectrode
was first prepared by spin coating, and the performance of the photoelectrode was
improved by coating a buffer layer, a protective layer, and a co-catalyst. The buffer
layer improves the properties of the BiVO4 structure, making the grain moreuniform and complete. At 1.2 V vs. RHE, the photocurrent is increased by 33%,and the IPCE is increased from 16% to 34% at 400 nm. Loading of the NiOx cocatalyst improves the oxidation kinetics, shifting the oneset potential to thenegative side by 0.2 V vs. RHE of the water splitting reaction, but the current in
the high-bias region is suppressed, indicating that there are also problems with theinterface and surface. The property of the protective layer TiO2 is similar to that
of a transparent conductive oxide (TCO), which can effectively reduce the
recombination of electron-hole pairs at the interface between the semiconductorand the electrolyte.
After that, we selected the BiVO4/SnO2 photoelectrode with the highestphotocurrent properties to test the stability under different electrolytes and pH
environments, and found that the borate buffer solution at pH=10 showed the best performance.
By using TEMPO as the mediator, we have demonstrated a electrochemicaloxidation of HMF into FDCA. When 78 C was passed, HMF had a conversion
rate of 74%, FFCA and FDCA had 29%, 30% yield, and 40%, 41% selectivity,Faraday efficiency is 91%. From the calculation of the concentration change, we
conclude that HMF is a first order reaction. |
