利用表面修飾自組裝合金/奈米複合碳材料與其電化學特性研究

Self-Organization and Electrochemical Properties of Metal and Alloy-Coated Carbon Nanotubes

周允文(Yun-Wen Chou)

指導教授 ： 謝建德

元智大學/工程學院/化學工程與材料科學學系/碩士(2007年)

https://doi.org/10.6838/YZU.2007.00088

摘要

本文提供一種自組裝合成多成份奈米纖維之技術，以多層奈米碳管為母體(matrix)，經此技術形成複合奈米碳纖維流程包括(a)植佈酸性官能基(表面氧化處理)、(b)離子交互作用及(c)熱處理三步驟，藉由金屬水合離子與CNT表面具有偶極距官能基之間的引力作用，而使CNT表面鍵結金屬，組裝奈米金屬顆粒於CNT上。藉由此技術可合成金屬及合金奈米顆粒於奈米一維碳材表面，形成複合奈米纖維。本文將實驗分為兩部份，其一為Ni/CNT之製備與電化學特性探討。第二個則是PtRu/CNT之製備與電化學特性探討。
第一部份中我們討論到Ni/CNT之製備與電化學特性探討，利用此表面改質技術，可以得到不同比例的Ni/CNT複合材料，從TEM與N2物理吸附分析可得知Ni奈米顆粒均勻分散且顆粒介於30–50 nm。利用電化學法測試並試著推算金屬負載於CNT表面上之電化學活性，從CV圖中可以經由分析得到電容量與Ni的負載量成一線性關係。我們可以把整體電化學活性的提升歸因於Ni奈米顆粒附著於CNT上，進而提供氫吸附/脫附活位所致。根據CV與交流阻抗的雙重測試，我們得知Ni奈米顆粒於KOH鹼性電解質中可得到217 F/g的電容量。經由充電/放電測試，此複合電池經50次的循環後仍具有很好的穩定性。
第二部份為PtRu/CNT之製備與電化學特性探討，我們從TEM、XRD與N2物理吸附分析得知，隨著Ru比例的增加，PtRu觸媒的晶相大小會呈一減少的趨勢(從4.34 nm變為2.77 nm)。我們發現PtRu/CNT複合材料的比表面積與孔徑分布在Pt與Ru負載後有些微的改變。利用CV在1M 的H2SO4電解液中實驗，樣品(Pt75Ru25)在此酸性電解質系統與甲醇氧化電化學測試中表現出非常良好的電化學活性(活性表面覆蓋率約84.6 %、高的If/Ib值與低的onset電位)。結果中電化學活性的增加，我們可以歸因於兩個原因：(a)雙金屬觸媒中，Ru的加入使得H2O電解之需求電位降低並促使碳基材氧化；(b)PtRu觸媒中，Ru的存在使Pt-COads易於還原。

關鍵字

自組裝機制、奈米碳管、循環伏安法、電化學活性、Ni奈米顆粒、PtRu奈米顆粒

並列摘要

In the present work, we propose an efficient method to fabricate metal particulates deposited on CNTs, which consists of the following steps: (a) implantation of acidic groups, (b) ionic interaction, and (c) heat treatment. In the self-organization nanostructure, the major formation mechanism is to utilize the strong interaction between metal ions and oxygen functional groups and the sidewall of carbon nanomaterials.The paper was divided into two parts:
Part 1. The electrochemical activity of an electrode of carbon nanotubes (CNTs) attached with Ni nanoparticles was investigated. A surface modification technique enabled different Ni particle densities to coat onto the CNT surface, which was chemically oxidized by nitric acid. It was found that each nickel nanoparticle has an average size of 30–50 nm, and the Ni-attached CNTs still possessed a similar pore size distribution. Cyclic voltammetry measurements in 6 M KOH showed that the electrochemical adsorption and desorption amount of hydrogen is a linearly increasing function of the Ni loading. This enhancement of electrochemical activity was ascribed to a fact that Ni particle acts as a redox site for hydrogen storage, thus leading to a greater specific peak current. According to our calculation, the electrochemical capacitance of nickel nanocatalyst in KOH electrolyte was estimated to be the value of 217 F/g. Charge/discharge cycling demonstrated that the Ni-attached CNT electrode maintains fairly good cycleability during 50 cycles.
Part 2. CNT decorated with bimetallic platinum/ruthenium nanocatalysts were fabricated to investigate their electrochemical activity in acid solution. These PtRu/CNT composites were characterized by transmission electron microscopy (TEM), X-ray diffraction (XRD), and N2 physisorption. The crystalline size of PtRu nanocatalysts generally decreased with Ru atomic ratio, i.e., form 4.34 nm to 2.77 nm. The specific surface areas and pore size distributions of PtRu/CNT composites were slightly altered after the PtRu deposition. Cyclic voltammetry measurements in 1 M H2SO4 and in 0.5 M H2SO4 containing 0.5 M methanol showed that Pt75Ru25/CNT electrode has the greatest activity in electrochemical adsorption and desorption of hydrogen, i.e., the ratio of electrochemical surface coverage: 84.6 %; the higher If/Ib value and lower onset potential. This enhancement of electrochemical activity was attributed to two possible reasons: (a) addition of Ru in the bimetallic catalysts leads to reduce the required potential for water electrolysis and thus the associated carbon oxidation; (b) the presence of Ru in the bimetallic alloys acts an important role in regenerating inactive Pt–COads sties.

並列關鍵字

Self-organization ； Carbon nanotubes ； Electrochemical activity ； Cyclic voltammetry ； Ni nanoparticles ； PtRu nanoparticles

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