利用掃描式電子穿隧顯微鏡觀察一氧化碳分子在釕、錫修飾過的鉑(111)電極上的電氧化現象;Electro-oxidation of carbon monoxide on Ru or Sn-modified Pt(111) electrode by in situ Scanning Tunneling Microscopy

Please use this identifier to cite or link to this item: http://ir.lib.ncu.edu.tw/handle/987654321/54123

Title:	利用掃描式電子穿隧顯微鏡觀察一氧化碳分子在釕、錫修飾過的鉑(111)電極上的電氧化現象;Electro-oxidation of carbon monoxide on Ru or Sn-modified Pt(111) electrode by in situ Scanning Tunneling Microscopy
Authors:	程琬君;Chen,Wan-Chung
Contributors:	化學研究所
Keywords:	鉑(111);釕修飾;錫修飾;掃描式電子穿隧顯微鏡;一氧化碳氧化過程;直接甲醇燃料電池;DMFCs;Pt(111);Ru-midified;Sn-modified;EC-STM;CO oxidation
Date:	2012-07-20
Issue Date:	2012-09-11 18:36:52 (UTC+8)
Publisher:	國立中央大學
Abstract:	本論文利用掃描式電子穿隧顯微鏡(in situ scanning tunneling microscopy, STM)及循環伏安法(cyclic voltammetry, CV)觀察一氧化碳分子在無修飾及釕、錫修飾後鉑(111)電極上的吸附結構及電氧化過程。首先在無修飾鉑(111)電極上，單層一氧化碳分子氧化所需的時間與施加電位有密切的關係，從電流對時間實驗的結果發現，電位愈正，一氧化碳分子氧化愈快，雖然一氧化碳的主要的氧化峰出現於0.8 V(對可逆氫電極)，但氧化電流在0.4V就已經出現，雖然此一電流只有10微安/cm2，但STM結果顯示此時一氧化碳分子緩慢的氧化成甲酸分子於吸附於電極上，據此我認為吸附於鉑電極上之一氧化碳分子早於0.4V既已開始氧化，只是受制於水的分解反應，因此一氧化碳分子以極慢的速率進行氧化。氧化反應主要發生在台階邊緣與缺陷處，但在平台上也會隨機發生反應。電解質的種類與電解液濃度也會影響一氧化碳分子氧化的速率;提高電解液的濃度延緩一氧化碳分子的氧化。經釕金屬修飾過後，鉑(111)電極上一氧化碳分子的吸附強度及其氧化過程有明顯的變化。當電解液為過氯酸時，一氧化碳分子會優先從台階邊緣發生氧化，但釕金屬的邊緣並無優先氧化的現象。增加釕金屬的覆蓋度導致一氧化碳分子全面及快速的氧化。但在硫酸中，吸附於釕金屬的周邊以及台階邊緣的一氧化碳分子會優先被氧化。為更進一步了解修飾物種類對鉑(111)電極催化一氧化碳氧化，我也研究錫金屬的修飾，藉由STM觀察到一氧化碳會優先從錫金屬的周邊與台階和缺陷的邊緣發生氧化，而氧化反應的速度在活性高的區域氧化完成後趨於平緩，和釕修飾的結果相比，發現一氧化碳分子的氧化速率較慢，此一差異可能和釕及錫修飾物對水在鉑電極上的氧化有明顯的不同的影響。Reported here is in situ STM imaging results recorded in the course of carbon monoxide electro-oxidation on bare and modified Pt(111) electrodes. The modifiers studied here are Ru or Sn, which are known to effect the activity of Pt(111) toward electro-oxidation of CO admolecules. First, the dynamics of oxidation of CO admolecules was examined as a function of potential. Chronoamperometric results show that the time span needed to stripe off a monolayer of CO admolecules varied from several hundreds seconds to a fraction of second, depending on the potential applied at the Pt(111) electrode. Accompanied by a small fraction of CO molecules adsorbed on terrace, those adsorbed at step edges and pits were oxidized first. In addition, the effects of [HClO4] and [H2SO4] on the dynamics of CO oxidation were also examined. It is found that the CO oxidation peak shifted positively by roughly 60 mV for every ten fold increases of the concentration of supporting electrolyte . The electro-oxidation of CO at Pt(111) electrodes coated with different amounts of Ru was studied in HClO4 and H2SO4. In HClO4, this reaction occurred at step edges first, rather than at the perimeters of Ru deposit assuming 3D clusters measuring in average 3 nm across. The more Ru deposit, the faster CO admolecules were oxidized. It is however peculiar to find that this oxidation reaction did not occur at surface sites near the Ru deposit. In comparison, the oxidation of CO admolecules commenced at surface sites near Ru clusters in H2SO4. On tin-modified Pt (111) electrode, CO molecules adsorbed to sites near Sn deposit and surface defects were oxidized first. CO admolecules were oxidized much slower on Sn-coated Pt(111) that those of Ru-modified Pt(111). It is speculated that these modifiers of Ru and Sn could facilitate the adsorption of water molecules needed to catalyze the oxidation reaction of CO admolecules. The former hastened the rate of water decomposition to OH species; whereas the latter facilitated the adsorption of water molecules at less positive potentials.
Appears in Collections:	[Graduate Institute of Chemistry] Electronic Thesis & Dissertation

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