石墨烯／矽異質結構在二氧化碳還原上的應用

Abstract

由於二氧化碳還原反應有助人類解決全球暖化問題並製造出各種高附加值化學品，近年來受各界的關注，其中尤以光電化學反應法被受矚目。在眾多光電化學電極材料中，矽因其較小的能隙而被廣泛使用，然而由於其不穩定性，使用時往往需要加上保護層，由於保護層材料一般導電性較差，導致觸媒難以在地生長以及最終元件效能低落。石墨烯是一種由單層碳原子所組成的二維材料，化學惰性使它成為合適的保護層材料，而且石墨烯可與矽形成蕭基接面促進載子分離，再加上它的導電性容許觸媒在地生長，能大幅提升元件的效能及穩定度。因此此論文的研究主體為如何將石墨烯與矽所組成之蕭基光電化學元件用作平台，以電鍍法生長觸媒，並最終用於還原二氧化碳。 在論文第一部分，我們在金字塔型矽基板上建立了石墨烯與矽之蕭基接面，並嘗試電鍍了銦錫及銅銀兩種觸媒，再借由拉曼光譜分析、掃描式電子顯微鏡、能量散射 X 射線譜、X 光繞射等分析方法，成功確認石墨烯與金字塔矽基板緊密貼合以及金屬觸媒的生長。第二部分中，此元件被用於進行光電化學的量測以及二氧化碳還原反應，通過吸收入射光，元件的起始電位皆右移了約 0.55 V ，並達成了在使用銦錫作觸媒時於-0.5 V vs. RHE 時甲酸的法拉第效率達到 72.1%，於使用銅銀作觸媒時於-0.5 V vs. RHE 時乙醇的法拉第效率達到 39.95%，多碳產物整體法拉第效率超過 50%。而且在長時間的穩定度量測後，元件由於石墨烯的惰性保護能力，表現仍然十分出色。

The photoelectrochemical carbon dioxide reduction reaction (PEC CO2RR) is one of the most promising approaches to solve the problem of global warming by using CO2. Silicon is one of the most widely used photoelectrode materials due to its small bandgap. However, because of its instability, a protective layer is often needed. Since the protective layer material in most cases has poor conductivity, in-situ growth of catalysts becomes difficult, and results in low device performance. Graphene is a two-dimensional material composed of a single layer of carbon atoms, it has various characteristics including chemical inertness, excellent electrical conductivity, and can form a Schottky junction with silicon to promote carrier separation. Therefore, graphene is a good protective layer candidate that can also allow in-situ growth of catalysts, thus greatly improve the performance and stability of a CO2 reduction device. Hence, the main purpose of this thesis is to investigate the application of a graphene-silicon Schottky junction device with electrodeposited catalysts in PEC CO2RR, and finally use it to reduce carbon dioxide.

In the first part of this thesis, a Schottky junction was formed between graphene and a pyramid-shaped silicon substrate, and electrodeposition of two catalysts, InSn and CuAg, was attempted. The close adhesion of graphene to the substrate and the growth of the catalysts were confirmed through Raman spectroscopy, SEM, EDX, and XRD. In the second part, photoelectrochemical characterizations of the devices were performed, and their performances in CO2RR were studied. Through absorbing energy from the incident light, the onset potential of the element shifted rightward for about 0.55 V. When the InSn catalyst was used, the Faradaic efficiency of formic acid reached 72.1% at -0.5 V vs. RHE. When the CuAg catalyst was used, the Faradaic efficiency of ethanol reached 39.95% and the Faradaic efficiency of multi-carbon products exceeded 50%. A stability study was also performed, confirming the device remained stable due to the protection of graphene.