以雙胞光反應器利用鈦酸鍶與釩酸鉍進行光催化水分解並同時分離氫氣及氧氣

Abstract

在全球暖化和能源危機的衝擊下，研發替代石油的永續能源是刻不容緩的議題。氫能因其具備永續發展的應用潛力被廣為研究，其中光催化水分解所產生的氫氣更是屬於零碳排的綠色氫能。在此過程中光觸媒受到太陽光激發將水分解為氫氣與氧氣，進行光能與化學能的轉換與儲存。 本研究將光觸媒鈦酸鍶(SrTiO3)及釩酸鉍(BiVO4)納入設計，並使用雙胞光反應器構成Z型系統，達到高光催化活性、高穩定性、高效率分離的光催化水分解。產氫研究方面，吾人利用熔鹽法合成出一系列鈦酸鍶光觸媒並進行光催化探討與材料分析。其中以氯化鍶水合物作為熔鹽在攝氏1150度進行鍛燒合成出的鈦酸鍶，搭載光沉積的銠鉻金屬粒子後達到最高的278 μmol h-1 g-1氫氣產率。產氧研究方面，吾人利用水熱法以不同環境及條件進行釩酸鉍光觸媒合成，以探討水熱環境與光催化活性的交互作用。其中在pH 2水熱10小時及混摻5 mol%鈷金屬的合成條件下，可以達到最高的493 μmol h-1 g-1氧氣產率。 在雙胞光反應器中吾人利用鈦酸鍶搭載銠鉻金屬粒子做為產氫光觸媒，釩酸鉍混摻鈷金屬作為產氧光觸媒。以鐵/亞鐵離子系統作為電子媒介及Nafion陽離子交換薄膜隔離兩種光觸媒以組成雙胞反應器。此Z-scheme的雙胞反應器成功達到在光催化水分解生產氣體並同時分離氫氣與氧氣。不僅避免氫氣與氧氣再結合，更減低額外的分離成本與爆炸風險。本研究成果帶進光觸媒在實際應用上的價值。

With global warming and the energy crisis deteriorating, it is an urgent issue to develop alternative energy sources to fossil fuels. Hydrogen has been widely studied as sustainable energy with broad application potential. Moreover, the hydrogen generated by photocatalytic water splitting is known as green hydrogen, producing zero-carbon emissions. In this process, photocatalyst could absorb sunlight and decompose water into hydrogen and oxygen, i.e., convert solar energy into chemical energy. In this work, photocatalysts, including strontium titanate (SrTiO3) and bismuth vanadate (BiVO4), were studied and then further applied in a twin photoreactor to comprise the Z-scheme system. So photocatalytic water splitting achieved high photocatalytic activity, high stability, and high-efficiency separation of gaseous products. For the hydrogen evolution, a series of SrTiO3 were synthesized by the flux molten-salt method and carried out their characterization and photoreaction. The results showed SrTiO3 synthesized using SrCl2·6H2O as molten salt at 1150°C calcination and loaded with cocatalyst, RhxCr2-xO3, by the photodeposition showed the highest hydrogen-evolution rate of 278 μmol h-1 g-1. For oxygen evolution, a series of BiVO4 were synthesized by the hydrothermal method under different situations to evaluate the correlation between photoactivity and the hydrothermal conditions. The results showed that Co-doped BiVO4 synthesized at a pH value of 2 and a period of 10 hours reached the highest oxygen-evolution rate of 493 μmol h-1 g-1. In the twin photoreactor, RhxCr2-xO3/SrTiO3 was used as the hydrogen-evolution photocatalyst, and BiVO4 was used as the oxygen-evolution photocatalyst. Ferric/Ferrous ions served as electron media, and a cation-exchanged Nafion membrane divided the two photocatalysts in the twin photoreactor. As a result, the Z-system of the twin photoreactor can separate hydrogen and oxygen simultaneously during photocatalytic water splitting, thus not only avoiding the recombination of hydrogen and oxygen but also reducing additional separation costs and explosion risk. This research brings in the value of photocatalysts in practical applications.