Z-scheme 光催化進行水分解產氫

Abstract

Z-Scheme 是一種利用兩種光觸媒進行水分解產氫的系統，而光觸媒可分為產氫觸媒與產氧觸媒兩種，分別進行產氫與產氧的反應。過去使用Z-Scheme 來進行光催化水分解反應時，都是將兩種光觸媒混合後再進行照光反應，所以產生的氣體是氫氣和氧氣的混合氣體，不但會發生逆反應，降低水分解效率，更有爆炸安全上的顧慮，而且氫氣尚須經過分離的步驟才可使用。故本實驗是以Pt/SrTiO3:Rh作為產氫觸媒，以WO3作為產氧觸媒，分開至兩個連結式的反應器中，以Fe3+/Fe2+為電子傳遞媒介在水溶液中，利用Nafion 離子交換膜隔開兩觸媒，照射可見光進行光催化水分解反應，以達到氫氣與氧氣及時分離的效果。實驗是以500W鹵素燈作為可見光源，使用經過Fe3+前處理的Nafion 膜進行反應，由結果發現確實可以做到氫氣與氧氣分開生成的效果，且與單一反應器系統相比，由於阻止逆反應的發生，使其具有更高的產氫和產氧產量，而在最佳的條件下，產氫速率可以達到2.22 μmol/g-hr且符合H2:O2=2:1的水分解化學當量比。

The Z-scheme is a two-photocatalyst system for photocatalytic water splitting to produce hydrogen. The two-photocatalyst system is comprised of H2-catalyst and O2-catalyst to produce hydrogen and oxygen, respectively. Conventionally in Z-scheme, two catalysts are mixed in one reactor to perform photocatalytic water splitting, thus hydrogen and oxygen are produced as a mixture. Thus, the reverse reaction occurs to reduce the efficiency of water splitting. The cost of H2 separation is another drawback. Furthermore, a safety issue of H2-O2 explosion must be considered in the commercial process. This research used Pt/SrTiO3:Rh (H2-catalyst) and WO3 (O2-catalyst) discretely in two compartments of a connected twin reactor filled with aqueous solution. Two compartments of the twin reactor was separated by Nafion ion-exchanged membrane. Fe3+ and Fe2+ were added and served as electron-transfer mediates for redox reaction. The Nafion membrane was pretreated under Fe ion solution. The light source was 500W Halogen lamp. Under the visible-light irradiation, hydrogen and oxygen can be separately produced in two compartments simultaneously by photocatalytic water splitting. Under the optimal condition, the H2 yield reached 2.22 mole/g-h, and the molar ratio of H2/O2 was matched the stoichiometry of water splitting.