以硫化鎘奈米鈦管與氧化鎢進行可見光催化甲酸溶液分解產氫之研究

Abstract

化石燃料日漸枯竭，研發與推動新能源技術刻不容緩，其中，氫能源是現階段被認為最具潛力的替代能源，使用後唯一產物即為水，然而，如何生產、儲存、輸送氫能源仍為目前一項重要的挑戰。近年來，許多研究利用光觸媒分解水產氫，其中雙觸媒系統又稱為Z型反應，是一種利用兩種光觸媒進行水分解產氫的系統，在系統中加入產氫觸媒及產氧觸媒，分別進行產氫及產氧的反應，相較於單純置入產氫觸媒的單觸媒系統而言，可提升水的分解效率。亦有研究指出，甲酸能夠有效的儲存氫氣並擔任電洞捕捉劑，延緩電子、電洞對再結合。因此本研究為提升二氧化鈦光觸媒之甲酸溶液分解產氫效率，將其製備為奈米鈦管並批覆上硫化鎘及貴重金屬鉑，硫化鎘可有效的轉移吸收光譜至可見光區，而鉑可提高觸媒活性、延長電子電洞對分開的周期，將此改質之產氫觸媒與產氧觸媒氧化鎢置於甲酸溶液中進行產氫研究。 常溫下以150 W可見光燈管催化10 vol%甲酸溶液，以0.2 g產氫觸媒與0.2 g產氧觸媒置於200 mL甲酸溶液中為本研究之最佳觸媒劑量比例。雙觸媒系統之CdS/TiO2+WO3於10 vol%甲酸溶液中，高出僅加入CdS/TiO2之單觸媒系統將近九倍。相較於TiO2，TNTs之高比表面積可使較多CdS批覆於其上，其產氫效率為115.5 μmol．h-1，大約為CdS/TiO2+WO3的四倍。而以CdS/TNTs+WO3為觸媒進行甲酸濃度的探討，可發現以20 vol%甲酸溶液擁有最高的產氫效率，產氫效率可達247.8 μmol．h-1。利用無電電鍍法批覆Pt之0.01 wt%Pt/CdS/TNTs與WO3於20 vol%甲酸溶液中具有最好的產氫效率，高達852.5 μmol．h-1。

Hydrogen gas is one of the most promising renewable energy nowadays and the final product of hydrogen combustion is nothing but water. However, it is still a big challenge to produce hydrogen gas and store it. Therefore, many researches have been conducted to produce hydrogen from water using photocatalysts. The Z-scheme photocatalysis is a two-photocatalyst system that comprised H2-catalyst and O2-catalyst to produce hydrogen and oxygen, respectively. Comparing to one step system, the two step system could promote the efficiency of water splitting. On the other hand, formic acid has been seemed as a convenient hydrogen-storage material recently and can be safely handled in aqueous solution. Therefore, this study investigated the photocatalytic conversion of formic acid solution to hydrogen gas using visible light (150 W, 350 < λ < 800 nm) with several types of H2-catalysts (CdS/TNTs, CdS/TiO2, Pt/CdS/TNTs, Pt/CdS/TiO2) and WO3 as the O2-catalyst. The optimum photocatalysts doses in the solution were investigated first and the results showed that the best doses were 0.2 g H2-catalysts and 0.2 g O2-catalyst in 200 mL solution. The hydrogen production with 10 vol% formic acid solution over CdS/TiO2+WO3 (two step system) was 30.2 μmol．h-1, which is about nine times higher than that with CdS/TiO2’s (one step system). Due to the high specific surface area of TNTs, more CdS could be attached onto the TNTs surface than to with that of TiO2’s, so the yield of hydrogen is much higher with CdS/TNTs+WO3 than CdS/TiO2+WO3. The hydrogen production with CdS/TNTs+WO3 achieved 115.5 μmol．h-1, which is about four times higher than that with CdS/TiO2+WO3. This study also investigated the optimum concentration of formic acid and the results showed that the hydrogen production with 20 vol% formic acid solution over CdS/TNTs+WO3 achieved 247.8 μmol．h-1, which is the highest. Moreover, coating of metal ions onto the photocatalysts could further promote the reaction. In this study, Pt coated onto CdS/TNTs was prepared by electroless plating in order to reduce recombination of holes and electrons. Results showed that the optimum amounts of metal was 0.01 wt%, which hydrogen production achieved 852.5 μmol．h-1 with 20 vol% formic acid solution.