| 摘要: | 鉑已是廣泛應用的催化劑和電催化劑，但是單金屬鉑在催化和電催化過程中容易失去活性或被反應的中間產物所佔據導致中毒。其中一氧化碳(CO)是一明顯的範例，CO會吸附在鉑的表面，可能佔據其活性位置，阻斷原本可發生反應的途徑，這種現象稱為”CO毒化”(Carbon monoxide poisoning)，開發一可抗CO毒化的陽極催化劑關係到燃料電池的效率，對未來的能源發展具一定的重要性。
本研究以雙金屬合金Pt3Co(111)電極為出發點，在以光電子光譜(XPS)與射線繞射(XRD)確認其化學成分及晶格排列，並藉由掃描式穿隧電子顯微鏡觀察其表面結構後，探討其對抗CO毒化及催化氫氣氧化之特性。
與Pt(111)電極相比，單層一氧化碳在Pt3Co(111)電極上，氧化剝除的主峰向負偏移約0.06 V，此氧化波的電量只有240 C/cm2，相對於Pt(111)電極的360 C/cm2 明顯低很多，意味者吸附之CO分子並未完全覆蓋Pt3Co(111)電極。此一結果也和在-0.25和0.05 V間仍然有氫原子(Hupd)吸附在Pt3Co(111)的現象一致。Hupd會影響氫氧化反應電流，與純Pt(111)相比，Pt3Co(111)電極氫之氧化電流，於移除Hupd後驟升。
STM結果顯示Pt3Co(111)電極表面有寬廣之平台與單原子台階，在平台上發現一氧化碳吸附形成之c(4 x 2)結構，其覆蓋度為0.5(CO/Pt)，低於Pt(111)的0.75，這和上述的電化學結果相呼應。此外表面反射紅外光譜結果表明，電極內層鈷元素影響鉑表面吸附一氧化碳之強度及吸附量。
Pt3Co(111)電極上氧氣還原反應，根據 Koutecký–Levich 方程式計算的結果，轉移電子數為3.975，推測氧氣主要經由4電子途徑還原為水。對甲醇氧化反應而言，Pt3Co(111)電極，產生兩倍於Pt(111)氧化電流，此一活性可歸功於CO高容忍度。
;In recent years, platinum (Pt) has been widely used as a catalyst and electrocatalyst. However, monometallic platinum is easily deactivated or poisoned during electrocatalytic processes. Among them, carbon monoxide (CO) is an obvious example. CO will adsorb on the surface of platinum, which probably occupy its active position and block the original path that could react. This phenomenon is called "CO poisoning". An anode catalyst that is resistant to CO poisoning is related to the efficiency of the fuel cell and has significant importance for future energy development.
This study is based on the bimetallic alloy Pt3Co(111) electrode, and its chemical composition and lattice arrangement are confirmed by photoelectron spectroscopy (XPS) and ray diffraction (XRD). After observing its surface structure with a scanning tunneling microscope (STM), we explore its ability of CO tolerance and electrochemical characteristics of catalytic hydrogen oxidation.
Compared with the Pt(111) electrode, the main peak of the single-layer carbon monoxide stripping on the Pt3Co(111) electrode shifted negatively by 0.06 V, and the charge of this oxidation wave is only 240 C/cm2, which is much lower than the 360 C/cm2 of the Pt(111) electrode. It means that adsorbed CO molecules do not completely cover the Pt3Co(111) electrode. This result is also consistent with the phenomenon that hydrogen atoms (Hupd) are still adsorbed on Pt3Co(111) between -0.25 and 0.05 V. Furthermore, Hupd will also affect the hydrogenation reaction current. Compared with Pt(111), the hydrogen oxidation current of the Pt3Co(111) electrode increases rapidly after removing Hupd.
STM results revealed that the surface of the Pt3Co(111) electrode is composed of broad terraces and monoatomic steps. c(4 x 2) structure formed by carbon monoxide adsorption was found on the platform, and its coverage was 0.5 (CO/Pt) lower than 0.75 of Pt(111), which is consistent with the above electrochemical results. In addition, Surface-Enhanced Infrared Absorption Spectroscopy (SEIRAS) results indicate that cobalt element in the inner layer of the electrode affects the strength and amount of carbon monoxide adsorbed on the platinum surface.
According to the calculation results of the Koutecký–Levich equation, the number of electrons transferred in the oxygen reduction reaction of the Pt3Co(111) electrode is 3.975, and it is speculated that oxygen is mainly reduced to water through the 4-electron pathway.
For the methanol oxidation reaction, the oxidation current generated by the Pt3Co(111) electrode is twice as large as that of Pt(111), and this activity can be attributed to the high tolerance of CO. |
