一氧化碳分子在鉛、銅修飾的鉑(111)電極上氧化及還原現象

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题名:	一氧化碳分子在鉛、銅修飾的鉑(111)電極上氧化及還原現象
作者:	黃建瑋;Huang, Jian-Wei
贡献者:	化學學系
关键词:	鉛;銅;一氧化碳氧化反應;一氧化碳還原反應;lead;copper;carbon monoxide oxidation reaction;carbon monoxide reduction reaction
日期:	2022-08-10
上传时间:	2022-10-04 11:00:13 (UTC+8)
出版者:	國立中央大學
摘要:	本論文利用循環伏安法(Cyclic Voltammetry，CV)和掃描式電子穿隧顯微鏡(Scanning Tunneling Microscope，STM)，探討在鉛修飾於Pt(111)電極上的結構及對於一氧化碳吸附和氧化的影響，另一部分為銅沉積於Pt(111)電極上於氫氧化鉀中形貌的變化及吸附和還原一氧化碳的過程。經過鉛修飾後一氧化碳的氧化電位提前60 mV，由STM結果得知鉛沉積的過程中首先會無序的吸附於Pt(111)電極上，隨著電位往負移動至-50 mV(vs. Ag/AgCl)產生覆蓋度為0.54的(7  57)結構，持續將電位往負移動至-250 mV產生(3  23) 覆蓋度為0.67及(21  21) 覆蓋度為0.59兩種不同的有序結構。加入一氧化碳後會破壞鉛薄膜，原先的鉛原子會被一氧化碳分子取代產生(2  2) 覆蓋度為0.75的吸附結構，隨著一氧化碳分子離開STM容槽，溶液中的鉛離子會重新吸附回Pt(111)電極與一氧化碳形成混合均勻的(3  7 ) 共吸附結構，鉛及一氧化碳覆蓋度均為0.22。此共吸附結構在電位往正移動時於缺陷處及相鄰有序吸附層間會開始出現氫氧根的吸附，因此斷定此為一氧化碳分子發生氧化的活性位點。沉積於Pt(111)電極上的銅膜在氫氧化鉀中移至-500 mV時會開始發生氧化，由旋轉電極可以測得銅膜在氧化的過程中會有溶解的現象，並且將電位往負移動至-800 mV後原先破碎的銅氧化物會還原為平整的金屬銅表面，證明銅薄膜在氫氧化鉀中的氧化還原過程具有可逆性，於-700 mV加入一氧化碳後觀察到氫氧根與一氧化碳共吸附的有序結構，該結構於-1 V時消失並且臺階邊緣出現許多亮點，可能為一氧化碳即將被還原的現象。 ;In this study, cyclic voltammetry (CV) and scanning tunneling microscope (STM) were used to explore the adsorption and oxidation of carbon monoxide (CO) on Lead-modified Pt(111) electrode. The electrified interface of a copper film supported by Pt(111) electrode in potassium hydroxide was also examined. The adsorption and reduction of carbon monoxide at this Cu film was revealed by in situ STM. After being modified by lead, the oxidation potential of carbon monoxide is shifted positively by 60 mV. STM results showed that lead was first adsorbed on the Pt(111) electrode in disorder in the first stage of deposition, yielding a (7  57) structure with a coverage of 0.54 at -50 mV (vs. Ag/AgCl). Shifting the potential negatively to -250 mV produced two different ordered structures, (3  23) and (21  21) with a coverage of 0.67 and 0.59. The addition of CO into the cell displaced the lead film at 0 V, leading to the renowned (2  2) – CO structure (coverage = 0.75). As the solution CO escaped from the STM cell, lead ions in the solution were adsorbed back to the Pt(111) electrode. STM imaging yielded a well ordered (3  7 ) structure, ascribed to homogeneously coadsorbed CO and Pb, whose coverages were both 0.22. As the potential was stepped to positive potential, aggregated features appeared the perimeters of mixed ordered domains, showing these sites were more active than the terrace site toward the oxidation of CO. In KOH the Pt(111) – supported Cu film started to oxidize at E > -500 mV (vs. Ag/AgCl). The rotating disk ring electrode was used to reveal that the copper film dissolved during the oxidation process, along with the formation of a rough oxide film. After switching the potential negative to -800 mV, copper oxide were reduced to expose a flat metallic copper surface. This kinetics of this reduction process was revealed by the in situ STM. After adding CO into the STM cell at -700 mV, an ordered (7  7) structure was imaged, which is ascribed to coadsorbed hydroxide and CO. This structure disappeared at -1 V and brighter rings appeared at the upper edge of the step, which is ascribed to CO reduction process. STM imaging revealed CO molecules were adsorbed on fcc and hcp sites on the Cu film having a Cu(111) texture. The two types of CO admolecules exhibited different corrugation heights.
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