利用掃描式電子穿隧顯微鏡研究一氧化碳分子在鉑(111)和釕修飾過的鉑(111)上的吸附結構及氧化過程; In situ STM study of the structure and oxidation process of carbon monoxide on Pt(111) and Ru-modified Pt(111) electrode

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题名:	利用掃描式電子穿隧顯微鏡研究一氧化碳分子在鉑(111)和釕修飾過的鉑(111)上的吸附結構及氧化過程;In situ STM study of the structure and oxidation process of carbon monoxide on Pt(111) and Ru-modified Pt(111) electrode
作者:	張聿介;Yu-chie Chang
贡献者:	化學研究所
关键词:	鉑(111);釕的覆蓋度;釕修飾過的鉑(111);掃描式電子穿隧顯微儀;一氧化碳氧化過程;Pt(111);Ru-modified Pt(111);Ru coverage;STM;CO oxidation process
日期:	2008-07-03
上传时间:	2009-09-22 10:18:45 (UTC+8)
出版者:	國立中央大學圖書館
摘要:	在此探討釕修飾層對鉑(111)單晶電極對一氧化碳的電催化氧化反應。主要的實驗變數為電解液的種類、釕的吸附量和RuCl3 溶液的pH值並且針對鉑(111)單晶電極浸泡RuCl3 溶液的時間長短來作統計，藉由釕的覆蓋度計算，我們可以得到覆蓋度對催化一氧化碳氧化的關係。由循環伏安法(Cyclic Voltammetry）觀察釕修飾過的鉑(111)電極在0.1 M 過氯酸溶液或硫酸溶液中的氧化還原圖。在過氯酸溶液中，結果顯示位於0.8 V附近的氫氧根的吸附-脫附的特徵峰明顯變小，而在硫酸溶液中，位於0.45 V的硫酸根的吸附-脫附特徵峰變小，這些結果和釕在鉑(111)電極上占據離子的吸附位置相關。另外由吸附在釕修飾過的鉑(111)電極上的一氧化碳氧化的CV圖可以發現，在一氧化碳氧化的電位區間有兩個明顯的氧化峰，其中較負電位的氧化峰為位於釕的島狀物周圍之一氧化碳的氧化，而較正電位的氧化峰為鉑電極上一氧化碳的氧化。藉由銅和鎘的低電位沉積(Underpotential deposition, UPD）可用以計算釕在鉑電極上的覆蓋度。鉑(111)電極在經過二次浸泡RuCl3溶液後，釕覆蓋度有明顯的提高，而較酸的 RuCl3溶液有利於釕的沉積。電化學-掃描式電子穿隧顯微儀（Electrochemistry - Scanning Tunneling Microscopy, EC-STM）結果顯示在釕修飾過的鉑(111)電極上，一氧化碳於0.1 V形成(2 × 2)的結構，當電位達到0.4 V時此一結構轉化為(√19 × √19)R23.1?的結構，並且觀察一氧化碳在到達氧化電位時的氧化過程，由STM圖可以發現一氧化碳在鉑(111)電極上與釕修飾過的鉑(111)電極上的氧化方式有明顯不同。在鉑(111)電極上，台階和缺陷上的一氧化碳較容易先發生氧化，而平台上發生一氧化碳氧化的地方較沒有一種明顯的規則，但是從之後的氧化過程中可以很明顯發現到，一氧化碳的氧化過程是從已發生氧化的區域逐漸擴散出去，於是一氧化碳分子吸附的區域逐漸減少，直到面上所吸附的一氧化碳完全氧化成二氧化碳。而在釕修飾過的鉑(111)電極上，釕的島狀物周圍區域很快發生一氧化碳氧化的現象，然後剩下未氧化的區域才逐漸氧化掉。 This study shows that the CO electrocatalytic oxidation on the surface of Pt(111) single crystal electrode and Ru-modified Pt(111) electrode. Compare to the CO oxidative efficiency in different electrolytes, the quantity of ruthenium and different pH of RuCl3 solution. We conduct the different immersion time by soaking the Pt(111) electrode in RuCl3 solution. And we make the statistics of Ru coverage to obtain the relation between the Ru coverage and CO oxidation. By using Cyclic Voltammetry to observe the CV profile of Ru-modified Pt(111) electrode in 0.1 M HClO4 and H2SO4 solution. In perchloric acid solution, we found the decreasing adsorption/desorption peak of hydroxide. And we also found the decreasing adsorption/desorption peak of (bi)sulfate in sulfuric acid solution. Therefore we know the Ru islands adsorbed on the Pt(111) electrode reduce the adsorption/desorption area of hydroxide or (bi)sulfate anion. Stripping of CO on Ru-modified Pt(111) produces two well-resolved current peaks. According to the ultra-high vacuum system literature, we speculate that the peak at more negative potential could originate from CO molecules chemisorbed at the perimeters of Ru islands deposited on Pt(111). The peak at more positive potential could arise from CO chemisorbed on the Pt domains away from the Ru islands of the Ru/Pt(111) electrode. The CO oxidation process has been assigned to the Langmuir-Hinshelwood mechanism. By using the underpotential deposition (UPD) of copper and cadmium, we can calculate the Ru coverage on Pt(111) electrode. In our experimental results, the Pt(111) electrode soaked in the RuCl3 solution by two times will increase the Ru coverage obviously. And we also found the RuCl3 solution (pH =2) will have the high Ru coverage. In situ scanning tunneling microscopy study of the CO adsorbed on Pt(111) electrode with and without Ru modifier. Starting at 0.1 V CO molecules were adsorbed in (2 × 2), which transformed to (√19 × √19)R23.1? at 0.4 V, before it was oxidized to CO2 at 0.7 V. On Pt(111) electrode, CO molecules were oxidized first at steps and defects. The oxidation fronts then moved into the terraces. But on Ru-modified Pt(111) electrode, CO molecules were oxidized uniformly on the surface, without noticeable preference at the perimeters of Ru islands.
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