Apply Modified TiO2/ITO Photocatalytic Thin Films to Water Splitting for Hydrogen Generation

[[abstract]]本研究旨在利用磁控直流濺鍍技術，製備二氧化鈦(TiO2)光觸媒薄膜，藉以探討應用此類光觸媒薄膜於水裂解產氫之可行性。本研究所製備的鍍膜，皆以氧化銦錫(ITO)導電玻璃作為基材，所製備的薄膜觸媒共有單純二氧化鈦、含氮二氧化鈦(N-TiO2-ITO)、含碳氮二氧化鈦(C N-TiO2-ITO)等三個系列，並設計一可調整外加電壓之水裂解光催化反應器，為實驗之所需。所探討的實驗參數，除了光觸媒薄膜本身特性之差異外，同時也測試不同無機鹽電解質種類與濃度，以及不同波長光源，對於產氫速率及光生電流強度之影響。 研究結果顯示：摻雜微量碳、氮之TiO2光觸媒，可提升其對可見光光源之吸收，已達初步紅移的目標，對於可見光下之光生電流的提昇，也有不錯的助益。不過，也可能因為改質後的觸媒，對於紫外光的吸收有減弱的現象，導致降低其在近紫外光下的產氫速率；就各類型二氧化鈦鍍膜之光生電流及產氫效能而言，本研究發現以未摻雜碳、氮之單純二氧化鈦鍍膜(T1)，具有最佳的反應效能，其原因與觸媒之表面結晶形貌、間隙大小、鍍膜厚度、能隙大小、光觸媒還原活性高低等因素有關。本研究中也發現，光觸媒氧化活性較低者(以氫氧自由基生成量為指標)，其產氫的效能愈佳，而且在偏鹼性的環境中，也具有較佳的產氫速率；另外，在不同電解質對產氫效能之影響方面，在所測試的三種犧牲試劑中，以Na2S與K2SO3混合液具有最強的光生電流，而Na2CO3及K2SO4則分別次之，不過不同薄膜觸媒各有其最適的電解質及濃度；最後，就不同光源之影響，在所測試的兩種光源中，以近紫外光(365 nm)其所產生的光電流強度，遠大於以可見光源(446 nm)所產生的光電流，其差異可達1~2個數量級，但碳、氮改質之光觸媒對於可見光下產氫效能的提升有助益。 綜合本實驗結果，其獲致之最高光生電流值分別為311 0 μA/cm2 (以365 nm為光源)及3 0 μA/cm2 (以446 nm為光源)，而可獲得之最大產氫速率，則是在以365 nm為光源下之2 9 μmole/cm2 hr，此時相當於光觸媒吸收每1 0 Watt-Hr光能量，可產生1 0910-3 mole的氫氣，高於許多文獻上的產氫效能。[[abstract]]This investigation is a feasibility study of applying TiO2/ITO (titanium dioxide/indium tin oxide) composite thin films as photocatalysts to hydrogen production from water dialysis Series of water splitting experiments were conducted in a photocatalytic reactor which was made of quartz and could be maintained at some constant levels of external voltages Three kinds of photocatalysts including simple TiO2 (TiO2-ITO) nitrogen doped TiO2 (N-TiO2-ITO) and carbon-nitrogen co-doped TiO2 (C N-TiO2-ITO) were investigated in the study The photocatalyst thin films were prepared in a DC magnetism spluttering reactor in which pure titanium foils work as metal sources and the ITO glass plates as deposition material The dope of nitrogen and carbon into crystal structures of TiO2 were expected to enhance photocatalyst’s responsibility of visible light Several experimental variables including types of photocatalysts types and concentrations of electrolytes (or scarifying agents) and types of light sources were tested in the study Both generated photocurrent and hydrogen yield rates during the tests under illumination both 365-nm near-UV light and 446-nm visible light were monitored Some important results were observed in this study It was observed that TiO2 could absorb longer-wavelength light after being doped with carbon or nitrogen but it may reduce the adsorption of ultraviolet light Among the tested photocatalyst thin films the simple TiO2-ITO produced higher photocurrent than rest two types of photocatalysts (N-TiO2-ITO and C N-TiO2-ITO) It may be caused by several possible reasons including surface characteristics of thin films energy gaps of photocatalysts thickness of films and activities of photocatalysts The experimental results also demonstrated that the photocatalysts with high oxidative capabilities achieved low hydrogen production rate and the photocatalyst had higher oxidative capabilities after being doped with nitrogen but they produced lower photocurrent Besides for the effects of irradiated light intensity on the H2 generation higher H2 producing rate could be achieved in higher irradiated light intensity and the rate under 365-nm light was 1~2 order higher than the rate under 446-nm light In addition for the effect of salts on the H2 generation the solution containing both Na2S and K2SO3 generally achieved higher H2 production rate than either Na2CO3 or K2SO4 solution This study successfully demonstrates the potential of applying TiO2/ITO thin film photocatalysts to hydrogen production from water splitting Summarizing the achieved results a highest photocurrent of 311 0 μA/cm2 was achieved when the photocatalysts illuminated with 365-nm near-UV light and a highest photocurrent of 3 0 μA/cm2 was achieved when the photocatalysts illuminated with 446-nm near-UV light The highest hydrogen yield rate that was achieved in this study could be as high as 2 9 μmole/cm2 per hou