以掃描式穿隧電子顯微鏡觀察氫氧化鎳於金(111)上結構及對甲醛氧化活性

Please use this identifier to cite or link to this item: http://ir.lib.ncu.edu.tw/handle/987654321/76729

Title:	以掃描式穿隧電子顯微鏡觀察氫氧化鎳於金(111)上結構及對甲醛氧化活性
Authors:	林廷駿;Lin, Ting-Chun
Contributors:	化學學系
Keywords:	電化學;甲醛氧化;金(111)
Date:	2018-08-15
Issue Date:	2018-08-31 11:34:37 (UTC+8)
Publisher:	國立中央大學
Abstract:	甲醛為常見的室內空氣汙染物，其濃度過高時會對人體造成傷害，包含森林大火、菸草煙霧、汽車尾氣等等都會產生甲醛，故而檢測甲醛有其必要性存在，而電化學的氧化還原反應十分迅速，可即時偵測溶液中的甲醛濃度，故研究可以提升甲醛氧化活性的觸媒，不但可用於檢測甲醛濃度，也可去除溶液中的甲醛或當作燃料電池的一個方向。　　此一研究以電化學方式將氫氧化鎳沉積於Au(111)電極表面，探討它對催化甲醛氧化的活性，並藉由掃描式穿隧電子顯微鏡輔助觀察其表面結構。實驗結果顯示Au(111)電極經1~2層氫氧化鎳修飾後，甲醛氧化電流從16.6提升至29.1 mA/cm2。在相同環境下，在Pt(111)上甲醛氧化電流為18.1 mA/cm2，顯示Ni/Au(111)電極大約有60%更高的活性。而從Koutecký–Levich方程式的計算結果得知，甲醛氧化反應轉移電子數在Au(111)和 Ni/Au(111)電極上，轉移電子數為0.94和2.6，經甲醛和[OH-]濃度變化的實驗結果推導出，甲醛氧化反應隨電極材料而不同，在金(111)為2HCHO+4OH-→2HCOO-+2H2O+H2+2e-，在Ni/Au(111)則是HCHO+3OH-→HCOO-+2H2O+2e-，原因可能是Ni的修飾導致其氫原子吸附自由能的改變。掃描式穿隧電子顯微鏡指出氫氧化鎳原子以六方最密堆積吸附於金電極上，於負電位區間其原子間距3 Å，而正電位時其間距縮減為2.8 Å，與文獻吻合，相對應電位主導之Ni(OH)2/NiOOH轉變。同時電極表面形貌在Ni(OH)2氧化為NiOOH後會由平坦轉變成三維球形顆粒。;Formaldehyde (HCHO) is a commonly used reducing agent for electroless copper deposition in the electronic industry. It can be an intermediate produced in the oxidation of small organic molecules such as methanol. In addition to the notorious poisoning effect of carbon monoxide on the performance of direct methanol fuel cells, incomplete oxidation of methanol can lead to formaldehyde and formic acid, resulting in a lower cell voltage and less efficiency than the predicted. Formaldehyde is also known as a common air pollutant, which comes from forest fires, tobacco smoke, automobile exhaust, etc. It is harmful to human body above a certain concentration. 　　In this study, nickel hydroxide was electrodeposited on the surface of Au(111) electrode to fabricate a composite electrode, which has been used to catalyze the oxidation of formaldehyde. Voltammetric results show that the oxidation current of HCHO at bare and nickel hydroxide modified Au(111) electrodes have peak current densities of 16.6 and 29.1 mA/cm2, as compared with 18.1 mA/cm2 observed at Pt(111). The nickel-modified Au(111) has about 60% higher activity than Pt(111). The Koutecký–Levich plots were constructed from the results of rotating disk electrodes of Au(111) and Ni/Au(111), yielding a total number of electron of 0.9 and 2.64. These results imply that the oxidation of HCHO at Au(111) electrode is 2HCHO+4OH-→2HCOO-+2H2O+H2+2e-,at Ni/Au(111) electrode is HCHO+3OH-→HCOO-+2H2O+2e-. STM shows that the surface morphology of the Ni film changed from smooth to rough structures with more positive potentials. It is possible to obtain atomic resolution images showing that the nickel hydroxide supported by Au(111) has a hexagonal close packed atomic structure with an interatomic distance of 3 Å in the negative potential region and transforms to a more closely packed lattice with a 2.8 Å in-plane distance in the positive potential domain.
Appears in Collections:	[Graduate Institute of Chemistry] Electronic Thesis & Dissertation

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