平整二維鉑於金載體及空氣下火焰法製備非貴金屬合金單晶的電催化

Please use this identifier to cite or link to this item: http://ir.lib.ncu.edu.tw/handle/987654321/85767

Title:	平整二維鉑於金載體及空氣下火焰法製備非貴金屬合金單晶的電催化
Authors:	廖偉呈;Liao, Wei-Cheng
Contributors:	化學學系
Keywords:	掃描穿隧顯微鏡;單層鉑;非貴金屬合金單晶製備;電催化;甲醛電氧化;X射線光電子光譜儀;鎳摻雜銅(111)
Date:	2021-08-17
Issue Date:	2021-12-07 11:22:44 (UTC+8)
Publisher:	國立中央大學
Abstract:	本論文包括兩個能源轉換為主題的研究。首先，鉑廣泛用於催化材料上，礙於礦產之稀有，人們極力尋找提升單位質量活性的方法。二維平舖的每顆鉑原子皆能和反應物接觸以貢獻反應，因此本實驗使用穩定度高且易前處理的金(111)乘載單層鉑。掃描穿隧顯微鏡(STM)發現金(111)上的單層鉑從0.278奈米被壓縮至0.269奈米，硫酸氫根及氫氧根的毒化因而減弱，因此與鉑(111)相比，單層鉑具有較高的氧還原(ORR)及氫催化(HO/ER)活性。氫氧根吸附會造成單層鉑的隆起，略微改善甲醇氧化(MOR)能力。雙層鉑在鉑(111)甲醇氧化峰電位下的電流是鉑(111)的1.7倍。一氧化碳間的斥力將鉑原子間距拉大至0.289奈米，因此吸附能異常增大。第二個研究改良貴金屬的單晶製備方法及器材。利用還原焰使非貴金屬再結晶，再用保護性氣體降溫以避免氧化。X射線光電子光譜(XPS)顯示無氧單晶銅表面僅有三層(1奈米)氧化亞銅。STM顯示高表面能(surface energy)的鎳並不存在退火後的銅鎳單晶表層。低濃度鎳(1.5 at%)摻雜能提升甲醛(HCHO)電氧化活性達十二倍；銅鈷合金並未觀察到此現象，因此應力效應(strain effect)影響不顯著。同位素取代實驗證明後續的氫氧鍵斷裂為新的速率決定步驟(RDS)。理論計算顯示底層鎳透過電子效應(electronic effect)增強表面數個銅原子對H2COOH-離子的吸附，因此微量的鎳即能顯著地改善催化活性。;Two subjects on energy conversion are studied in this thesis. First, to reduce the loading of Pt in catalyst, how to expose all the Pt atoms is an important issue. Two-dimensional Pt monolayer on Au(111) (Pt ML) can be fabricated by immersion of Au(111) in CO saturated aqueous Na2PtCl6 solution. After the stripping of capped CO, the bare Pt with hexagonally close-packed structure is exposed. Scanning tunneling microscopy (STM) shows the compressive strain on the Pt ML and the shrinkage of Pt radius from 0.278 nm for Pt(111) to 0.269 nm. This shrinkage results in the d-band center far away from the Fermi-level and thus weakens the adsorptions. This’s an advantage for hydrogen evolution/oxidation reaction (HE/OR) and oxygen reduction reaction (ORR) in sulfuric acid because the hydrogen atom and bisulfate adsorbs competitively with the reactants. However, weakening the adsorption of OH on Pt ML leads to a positive shift of the onset potential of methanol oxidation reaction (MOR). The OH adsorbs strongly at the step and thus lifts the atoms in a Pt ML. The caused island serves as an active site promoting the activity toward MOR. At the peak potential of MOR at Pt(111), the current for two-layered Pt is 1.7 times higher. Strong CO-CO repulsive interaction enlarges the Pt-Pt distance from 0.269 nm to 0.289 nm, making the d-band center close to Fermi-level. As the result, CO adsorbs surprisingly strong on Pt ML. The second research develops a tool and method for fabricating nonprecious metal single crystal (SC). Serving as a good catalyst for CO and CO2 electroreduction, Cu gains lots of studies recently. Owing to be willing to oxidize, doing the study on the SC is difficult. Modified commercial torch is used to recrystallize Cu in the reducing flame and enables the cooling in protecting gas flow. X-ray photoelectron spectroscopy (XPS) reveals 1 nm of Cu2O covers on an oxygen-free Cu SC. STM shows Ni with high surface energy is absent at the surface of annealed CuNi SC. Trace of Ni (1.5 %) enhances the activity toward formaldehyde electrooxidation by 12 times which is not seen with Co leading to the conclusion of strain effect is not the main reason. Isotopic substitution experiments show the cleavage of O-D bond in H2COOH- is the rate-determining step (RDS) at CuNi SC. Theoretical calculation suggests that Ni enhances the adsorption of H2COOH- on Cu via long-ranged electronic effect and thus greatly boosts the activity with few Ni atom.
Appears in Collections:	[Graduate Institute of Chemistry] Electronic Thesis & Dissertation

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