光催化水分解雙反應器之離子媒介傳輸現象

Mediated-ion transportation in a twin reactor for photocatalytic water splitting

游思淳(Szu-Chun Yu)

指導教授 ： 吳紀聖

國立臺灣大學/工學院/化學工程學研究所/碩士(2010年)

https://doi.org/10.6342/NTU.2010.02931

摘要

為尋求潔淨的替代能源，以光催化水分解方式製氫是極具有發展前景的途徑，Z-scheme系統乃是利用兩種光觸媒，分別進行產氫與產氧，並選擇適當離子還原對媒介用以傳遞電子。先前的研究指出，以薄膜分離產氫及產氧觸媒，僅讓離子對在膜中相互擴散，可以有效的讓氫氣跟氧氣分開產生，降低逆反應再結合成為水，產氫的效能也因此提升。本實驗針對薄膜分離式的反應系統，以比色法定量分析鐵離子對在Nafion膜中的擴散行為，由鐵離子的外顯擴散係數算得三價鐵離子每小時於最大濃度差2mM可擴散31.4μmol，而二價鐵離子之擴散速率則為44.2μmol/h，遠大於觸媒進行光反應生成氫氧的速率，顯示反應確實為水分解控制。產氫觸媒Pt/SrTiO3:Rh以固態熔融法搭配光沉積法製備，產氧觸媒則使用活性不同的WO3與BiVO4，並搭配產氫觸媒於Fe3+水溶液中進行單一混合型光反應，若與個別之半反應氣體產生速率相比，可觀察出全反應中的產氧速率受限於產氫端的較低活性而大幅下降，反應速率決定步驟落在產氫觸媒。而使用分離式反應器，由於減少了氫氧逆反應的機會，可提升產氫的速率，將兩邊觸媒分開也可解決觸媒之間混合在一起之光源競爭吸收問題，且觸媒在經過12小時的反應仍維持相同的氫氣平均產率，失活的情況幾乎可忽略。於最佳反應條件下，使用可見光源300W氙燈進行分離式光催化水分解，產氫速率可達0.88μmol/g．hr。

關鍵字

光催化 ； 水分解 ； 離子傳輸 ； 產氫技術

並列摘要

Hydrogen generation from photocatalytic water splitting has been so called the “artificial photosynthesis”, a green process that is promising and clean. The Z-scheme system is comprised of H2-catalyst and O2-catalyst with aid of electron transfer mediator to produce hydrogen and oxygen, respectively, mimicking the two step photosynthesis process. It shows that the seperation of H2-catalyst and O2-catalyst in two discrete chamber by Nafion ion-exchange membrane can efficiently increase the gas evolution rate due to backward reaction elimination from preveous research. In this report, the iron mediator transfer phenomenon through Nafion membrane was analyzed by colorimetry method quantitatively. The derived diffusion rates for irons were remarkably larger than photocatalytic hydrogen producing rate, indicating the real water splitting reaction. Besides, by applying different O2-catalyst (WO3 and BiVO4) along with H2-catalyst (Pt/SrTiO3:Rh) in water splitting reaction, the rate determining step has been shown to lie in H2-catalyst part. Furthermore, the twin reactor device can not only produce hydrogen and oxygen simultaneously in two chambers under visible light irradiation, but also eliminate the chance for light source competition between photocatalysts. Under the optimal condition, the hydrogen rate reached 0.88μmol/g．hr, and the deactivation could be negligible during 12 hours reaction time.

並列關鍵字

Photocatalytic water splitting ； ion transportation ； hydrogen evolution

參考文獻

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