掃描式電子穿隧顯微鏡及循環伏安法對有機碘化物在鉑(111)電極上的研究;An in situ Scanning Tunneling Microscopy and Cyclic Voltammetric Study of Aryl Iodide Molecules Adsorbed on a Pt(111) Electrode

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題名:	掃描式電子穿隧顯微鏡及循環伏安法對有機碘化物在鉑(111)電極上的研究;An in situ Scanning Tunneling Microscopy and Cyclic Voltammetric Study of Aryl Iodide Molecules Adsorbed on a Pt(111) Electrode
作者:	陳君琿;Jung-Huein Chen
貢獻者:	化學研究所
關鍵詞:	掃描式電子穿隧顯微鏡;有機碘化物;鉑(111);Pt(111);aryl iodide molecules;STM
日期:	2002-07-08
上傳時間:	2009-09-22 10:09:30 (UTC+8)
出版者:	國立中央大學圖書館
摘要:	Ⅰ. 含碘有機分子在鉑(111)電極上的吸附及反應：我們利用掃描式電子穿隧顯微鏡(STM)及循環伏安法(CV)探討在單結晶電極表面有機分子的吸附結構及其氧化還原反應，我們選定若干含碘之有機化合物，例如: 碘苯(IB)、碘庚烷(IH)、對-二碘苯(DIB)、氟碘苯(FIB)、4-碘苯胺(IN)、1,2-二羥基-4碘苯(DHIB)。因為它們在超高真空(氣固)界面已被研究，在此我們將著重於界面環境對分子吸附及反應的影響，我們將強調在電化學界面，電壓及電解液等因素對分子吸附的重要性。在0.1 M過氯酸中，電壓介於0.3至0.9 V之間，碘苯(IB)可完整地吸附於鉑(111)電極上。電壓較0.9 V正時，分子開始分解，生成碘原子及未知的有機碎片。在pH10的過氯酸鉀溶液中，可由還原脫附的電荷量計算出碘苯分子在鉑(111)電極上的覆蓋度為0.45。STM結果顯示，在0.3 V時有良好 (√7 ×√7)R19.1°結構，其覆蓋度為0.43，施以更正的電壓導致分子覆蓋度些微的增加至0.44，結構轉變成(3 ×3)。碘苯分子吸附在鉑(111)表面行成一(√7 ×√7)R19.1°的結構，其高解析STM圖像之形貌和單純的碘原子相同，顯示電子穿隧主要是經由和表面直接鍵結的碘原子端，其他的有機部分並未顯現明顯的影響。就結構而言，所有的有機碘化物分子均形成(√7 ×√7)R19.1°的結構，顯示出碘和鉑金屬的作用力掌控這些分子的吸附，有機的碳氫部分不具影響力。 Ⅱ. 以STM之探針操控局部銅的還原：在此我們將彰顯STM探針對電化學界面反應的影響，例如將鉑(111)電極電位設定於0.65 V時，雖然理論上此時不應有銅的還原反應，但如將探針電極之電位設定於0.45 V或更負，可造成以探針為中心，鉑電極上數百埃的範圍內銅的沈積，再將探針電位增加至0.7 V後，銅又從鉑電極上溶解，鉑載體的電位也會對這種由探針所操控的銅沉積反應，具有重要的作用，例如當鉑(111)電極電位為0.85 V或更正時，在可使用的電位條件下，探針無法控制銅的沈積。 Ⅲ. 苯硫酚在鉑(111)電極的吸附結構: 我們利用高解像STM檢測其吸附結構為(√3 ×√3)R30°，每個分子位於3-fold sites，覆蓋度為0.33。和碘苯分子的STM圖像比較，苯硫酚的結果顯示，有機苯的部分可能有參與電子的穿隧現象。 Ⅳ. 鐵、鉍、釕修飾層對一氧化碳在鉑(111)電極上氧化影響：作為燃料電池陽極的鉑金屬表面上，一氧化碳的吸附造成嚴重的毒化現象，阻斷了燃料分子如氫氣及甲醇等的氧化反應，而造成電池效能降低。本部分的研究是為了解鉑(111)電極上不同鐵、鉍、釕修飾層對CO氧化的影響。實驗證明釕金屬可提升鉑對CO氧化成為二氧化碳的活性。 We employed in situ scanning tunneling microscopy (STM) and cyclic voltammetry to study the adsorption of iodobenzene (IB) ?iodoheptane (IH) ?1,4-diiodobenzene (DIB)?1-fluoro-4-Iodobenzene (FIB) ?1,2-dihydroxy-4- Iodobenzene (DHIB) and 4-Iodoaniline (IN) molecules onto a well-ordered Pt(111) electrode in 0.1 M HClO4. These molecules were adsorbed intact without noticeable decomposition at potential negative of 0.9 V (vs. reversible hydrogen electrode), whereas degradation became prominent at potentials positive of 0.9 V. The coverage of the iodobenzene monolayer is estimated to be about 0.45 from the amount of charges involved in its reductive desorption in KClO4 (pH10) solutions. This value nearly equals that of iodine atoms at Pt(111). In situ STM was used to probe the spatial arrangements of these adsorbates as a function of potential in 0.1 M HClO4. A well-packed (√7 ×√7)R19.1° - iodobenzene structure predominated at 0.3 V, which readily rearranged into an (3 ×3) adlattice as a result of a slight increase of coverage at more positive potential. The STM appearances of these two adlattices resemble those of iodine atoms on Pt(111), suggesting that the contrast in STM arises mainly from the iodine head-groups. More negative potential resulted in desorption of iodobenzene molecules and a disordered adlayer. In contrast, iodoheptane molecules were disordered at potential negative of 0.7 V, but reorganization occurred to produce local (√7 ×√7)R19.1° at more positive potentials. These phase transitions were reversible to the modulation of potential between 0 and 0.9 V. Electrochemical potential dominated not only the chemical nature but also the spatial arrangements of the alkyl or aryl iodide molecules. The tip-and-sample interaction was noticeably stronger for iodoheptane, resulting in disordering of the adlayer. And all the other aryl iodide molecules are produce local (√7 ×√7)R19.1° at 0.2 V. With the tip of an STM, we can control the deposition/dissolution of Cu at an iodine-modified Pt(111) electrode. The deposition/dissolution events take place only underneath the tip allowing for a nanometer scale patterning of the Cu surface. The dissolution rate is shown to depend sensitively on the tip potential as well as on the electrode potential. The tip to sample distance also plays an important role in guiding these events. Lower feedback current and thus longer tip-to-sample distance appears to decrease the effect of the tip on the these processes. The adsorption of benzenethiol on Pt(111) from aqueous solution has been investigated by using scanning tunneling microscopy (STM) and cyclic voltammetry (CV). This molecule formed a well-ordered monolayer with a commensurate (√3 ×√3)R30° structure. The appearance of the STM molecular resolution of benzenethiol differs markedly from that of iodobenzene, suggesting the organic portion of adsorbates can have a different effect on the tunneling events. On Pt(111), the effect of sub-monolayers ruthenium deposit on CO oxidation has been investigated by using cyclic voltammetry (CV).The presence of Ru adatoms on Pt(111) resulted in a 200 mV negative shifts in potential of CO oxidation.
顯示於類別:	[化學研究所] 博碩士論文

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