無共觸媒二維異質結構光觸媒水分解產氫

Abstract

於石油日漸枯竭造成的能源危機下，尋求新的替代能源方案為當今之首要任務。氫氣因其高能量密度，作為新興能源是未來可期的。當利用光催化水分解產氫時，因水資源取之不盡的特色，且程序上乾淨無碳排，是永續綠色能源。 現階段光觸媒之挑戰主要來自於過快的電子電洞再結合速率。為解決此困境，傳統光觸媒常利用貴金屬共觸媒作為電子陷阱，將電子捕捉於表面，提高電子在觸媒表面反應之機率。本研究則是藉將鈦酸鍶、氮化碳兩種光觸媒混合，形成異質結構，分離電子/電洞，從而降低電子電洞於再結合之機率，進一步提升光催化水分解產氫活性。本研究發現，對氮化碳觸媒，利用一步剝離法可有效提高其剝離程度，其中以鍛燒2小時之氮化碳gCN_OS2具有最高之剝離程度，其產氫活性為7.18 μmol/g*hr；而對搭配之鈦酸鍶觸媒，使用2 mol%鎳摻雜、升溫速率1 ℃/min之水熱法製備的鈦酸鍶STOH1，其小粒徑有利於電子流通，將其與氮化碳混合後，可有效降低混合觸媒之阻抗。而混合觸媒10% 2Ni:STOH1/gCN_OS2於紫外光照射下，以三乙醇胺為犧牲試劑時，最高產氫活性可達285.4 μmol/g*hr，為純氮化碳觸媒活性的39.7倍。 於鎳摻雜鈦酸鍶-氮化碳混合觸媒中，其氫氣還原之反應位點由鈦酸鍶轉移至氮化碳上，形成Z型系統，不僅提高反應之驅動勢能，亦能顯著降低電子電洞對之再結合速率。 藉單波長LED光源進行之活性測試結果，當僅氮化碳被激發而鈦酸鍶未被激發時，活性大幅下降，故可認為兩觸媒間確實有交互作用，Z型系統對活性提升至關重要。透過Z型系統之結構，在無共觸媒附載的情況下，電子電洞再結合被有效抑制，仍可有效提升其光催化產氫活性。如此一來，相較傳統光觸媒，因無貴金屬共觸媒之附載，便可有效降低製備成本，提高光觸媒之發展性。

Because of the energy crisis, seeking new alternative energy solutions is important today. Hydrogen, with its high energy density, is a promising energy source. When hydrogen is produced from photocatalytic water splitting, the inexhaustible nature of water resources and the carbon-free process qualify it as a sustainable green energy. The current challenge for photocatalysts is the rapid recombination rate of electron-hole pairs. To address this issue, traditional photocatalysts often load noble metal cocatalysts on the surface as electron traps to capture electrons, which could increase the probability of surface reaction. This study combines strontium titanate (STO) and carbon nitride (gCN) photocatalysts, forming a heterostructural photocatalyst to separate electrons and holes and to reduce the recombination probability of electron-hole pairs, leading to the further increasing of hydrogen evolution activity. Here we show that the gCN catalyst could be effectively exfoliated using the one-step exfoliation method, gCN_OS2, exhibits the highest degree of exfoliation and demonstrates the highest hydrogen production efficiency of 7.18 μmol/g*hr. For STO catalyst, 2Ni:STOH1 prepared by hydrothermal method with a heating rate of 1 ℃/min and doped by nickel could possesses small particle size to be conducive to electron transport. When compounded with gCN, it effectively reduced the impedance. Under UV irradiation and using triethanolamine as a sacrificial agent, 10% 2Ni:STOH1/gCN_OS2 achieved a maximum hydrogen production activity of 285.4 μmol/g*hr, which is 39.7 times higher than that of the pure gCN catalyst. For Ni:STO/gCN catalyst, the hydrogen reduction active sites transfer from STO to gCN, forming the Z-scheme system. This not only enhances the driving potential of the reaction but also significantly reduces the recombination rate of electron-hole pairs. The results of activity tests conducted using a single-wavelength LED light source indicate a significant decrease in activity when only gCN is excited while STO remains unexcited. This suggests the interaction between the two catalysts and the critical importance of the Z-scheme system for enhancing activity. Through the Z-scheme system structure, the recombination of electron-hole pairs is effectively suppressed even without noble metal cocatalyst loading, thereby significantly enhancing photocatalytic hydrogen production activity. Thus, compared to traditional photocatalysts, the absence of noble metal cocatalysts can effectively reduce preparation costs and enhance the potential for photocatalyst development.