| 摘要: | 摘要 Ⅰ. 硫氧化物在金與鉑電極上之吸附反應 ??? 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硫氧化物的吸附結構及其氧化還原反應，我們特別選定兩種硫氧化物，例如：亞硫酸鈉(Na2SO3)、二硫亞磺酸鈉(Na2S2O4)。因為由許多CV文獻可知它們在不同電位下會形成不同價數的硫氧化物，在此我們將著重於界面環境以及相異的載體對分子吸附與反應之影響，強調在電化學界面狀態下，電位的改變對分子吸附的重要性，並探討硫氧化物在氧化反應發生時之電子轉移數。 [A]. 亞硫酸鈉： 由於亞硫酸鈉在酸性環境下能反應形成二氧化硫，故我們認為實驗中皆以二氧化硫吸附於不同電極上。由CV圖可知，二氧化硫吸附在金和鉑電極上時，其較易催化鉑電極，電壓介於0.05至0.9 V之間二氧化硫可完整吸附於鉑(111)電極上，電壓較0.9 V正時，分子開始氧化，生成高氧化態之硫氧化物(如：硫酸根)，再經由還原脫附產生硫原子而吸附於鉑電極上。STM結果顯示，二氧化硫吸附在金(111)上隨電位的改變形成三種結構，分別是當E＝0.2 V時為(5 × 2?39) R16.1°，E＝0.4 V轉為(?13 × ?21)R46.1°，E＝0.7 V轉為(5 × 3?7)R19.1°，其覆蓋度分別為0.14、0.21以及0.1。另一方面，二氧化硫吸附在金(100)上時，由於濃度的不同亦產生相異結構，在高濃度下，0.2 V時有良好(?2 × ?2)R45°結構，覆蓋度為0.5；在低濃度時，當E＝0.45 V會有兩種結構形成，分別為(?13 × 5?2)R45°，覆蓋度為0.16及(2?5 × 2?5)R26.6°，覆蓋度為0.22，施以更正的電壓導致分子覆蓋度增加和轉變成(2 × 2)覆蓋度為0.25的結構。此外，在鉑(111)電極之研究中，當電位控制於0.2 V，只觀察到(?3 × ?3)R30°結構，故推測此為硫原子的吸附。 [B]. 二硫亞磺酸鈉： 我們利用高解像STM檢測其在金(111)與鉑(111)電極上的吸附結構皆為(?3 × ?3)R30°，每個分子位於3-fold sites，覆蓋度為0.33。 Ⅱ. 聚?吩衍生物在鉑(111)電極的吸附結構 當電極電位設定於0.1 V時，由STM結果顯示，聚?吩衍生物(3TOESNa、P3TOESH)吸附於鉑(111)電極為(2 × 2)結構，覆蓋度為0.25，故猜測此一分子皆是以雜環上的π電子與金屬表面鍵結。 Ⅲ. 聚苯胺在鉑(111)電極之聚合情形 在CV結果中，於0.5和0.7 V分別有一對可逆氧化還原峰，且會隨掃描圈數而增加。此外，由STM亦觀察到在0.5 ? 0.7 V的電位範圍下，有明顯聚合情形發生。 Abstract In situ scanning tunneling microscopy (STM) has been used to examine the adsorption of sulfur-oxygen compounds (ex. sodium sulfite (Na2SO3) and sodium dithionite (Na2S2O4)) on well-ordered Au(111), Au(100) and Pt(111) electrodes in 0.1 M HClO4 under potential control. High-quality STM atomic resolution results in three adlattices on Au(111) immersed in acidic Na2SO3. These structures are presumably due to SO2, which represents the most prominent chemical species in the mixed solutions of HClO4 and Na2SO3. A well-packed (5 ? 2?39)R16.1? predominates at 0.2 V, which rearranges into a (?13 ? ?21)R46.1? adlattice as a result of a slight increase of coverage at 0.4 V. Finally, at 0.7 V clusters of sulfur atoms coadsorbed with water molecules to form a highly ordered adlattice of (5 ? 3?7)R19.1?. In situ STM was also used to probe the structures of SO2 on Au(100) in 0.1 M HClO4. With a concentration of 1 mM or higher, SO2 are adsorbed in (?2 ? ?2)R45?, ? ? 0.25, whereas at potential negative of 0.6 V lower concentration results in (?13 ? 5?2)R45?, ? ? 0.16 and (2?5 ? 2?5)R26.6?, ? ? 0.22, depending on the potential of Au(100). At more positive potential the coverage of SO2 ad-molecules increases to produce a more compact (2 ? 2), ? ? 0.25 structure. In the case of Pt(111), SO2 are spontaneously reduced to sulfur adatoms arranging in (?3 ? ?3)R30? at 0.2 V. The adsorption of Na2S2O4 on Au(111) and Pt(111) were also investigated by in situ STM and cyclic voltammetry (CV). In strong contrast to the formation of multiple adlattices for SO2, only one structure, (?3 ? ?3)R30?, is identified at Au(111) and Pt(111) by STM. Tentatively, according to the results from cyclic voltammetry, this structure, at least in the case of Pt(111), is due to the adsorption of sulfur adatoms, produced from the irreversible reduction of SO2 upon its contact with Pt electrodes. However, in the case of Au(111), no reduction feature is noted at potential negative of 0.3 V, indicating that S2O42- anions are adsorbed intact. Due to the close spacing (5.1 Å) of two neighboring S2O42- anions in the structure, they are likely to adsorbed through a sulfur atom. We employed in situ STM and CV to study the adsorption of poly-3-alkyithiophene derivatives (3TOESNa and P3TOESH) onto a well-ordered Pt(111) electrode in 0.1 M HClO4. The STM shows the atomic image of Pt(111) - (2 ? 2)-poly-3-alkyithiophene derivatives structure. Two nearest protrusions are separated by 0.55 nm. The atomic rows are parallel to the close-packed directions of Pt(111). In situ STM was also applied to study the electropolymerization of aniline on well-defined Pt(111) electrodes in 0.1 M HClO4. The two reversible peaks emerging at 0.5 and 0.7 V indicate the success of electropolymerization of aniline in the acidic media. High-resolution STM imaging of polyaniline on Pt(111) reveals the formation of electronically conducting organic phases with an average corrugation height of 6 nm. Stable STM imaging was possible for the first hour at 0.7 V in 1 mM aniline, whereas tip-and-substrate contact becomes so severe that it was impossible to have a clear view of the samples as the films get thicker. |
