金奈米顆粒製備及金、鉑觸媒之電化學活性比較

Gold Sols Preparation Using Methanol and Citrate and Test Its Electrochemical Activity

林俞吟(Yu-Yin Lin)

指導教授 ： 林昇佃

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.2007.00253

摘要

本研究目的是以探討檸檬酸鈉(citrate)-甲醇(methanol)還原製備金奈米顆粒並探討對電催化氧氣還原反應特性的影響，實驗以UV-vis分析金前驅物(AuCl3)還原程度，而以TEM分析金奈米顆粒粒徑及大小分布情形，並直接將金奈米顆粒用在電催化活性效能，分析其在液-固界面下氧化還原之能力及其動力學之行為，並嘗試比較金與鉑奈米顆粒的反應特性之差異，實驗以旋轉圓盤電極(RDE)來分析金與鉑電極在酸性系統下電化學氧氣還原反應及CO氧化的特性。
實驗結果顯示，甲醇在反應85℃下不足以還原氯化金(AuCl3)成為金奈米顆粒；而單用檸檬酸鈉在反應溫度60℃下即可還原前驅物，溶液顏色為酒紅色，顆粒近乎圓形，平均粒徑約為21 nm，且不會沉澱。在甲醇-檸檬酸鈉雙還原劑系統下，增加甲醇濃度會使溶膠顏色由酒紅色變為紫色，顆粒形狀為扁長形且顆粒平均大小為35 nm。當增加檸檬酸鈉濃度時，會使溶膠顏色由酒紅色變成黑紫色，顆粒形狀大小不一且容易聚集。
氧氣還原反應(ORR)測試發現，以Citrate/Au=1.5時，甲醇濃度增加，所得金顆粒的電催化活性變差，可見Au sol的顆粒大小會影響反應活性，顆粒愈小活性愈好，但仍低於鉑觸媒，活性大小依序為Pt black＞Pt disk＞Au sol＞Au disk。而在CO氧化反應測試部分，也可見金跟鉑電極的氧化反應特性有所不同；金電極在純CO氛圍下於1.05V處有一CO氧化峰，而在1% CO (in N2)下氧化電流約在1.2V處發生，白金電極在純CO氛圍在0.92V有強吸附CO的氧化訊號，而在1% CO in N2時強吸附CO發生在0.83V，且當CO濃度增加會使強吸附CO之Onset potential及peak potential變大，而溶液相CO隨著濃度增加而氧化電流增加。

關鍵字

奈米金顆粒 ； 旋轉圓盤電極 ； 酸性系統 ； 氧氣還原反應

並列摘要

This study uses citrate - methanol to prepare gold sols from AuCl3 and their electrocatalytic activities toward oxygen reduction reaction (ORR) and CO oxidation are analyzed. Rotating Disk Electrode (RDE) is used to illustrate the effect of mass transfer on the measured electrocatalytic activity. The activity of gold is compared to that of platinum electrode.
Experimental results show that AuCl3 precursor cannot be reduced to gold nanoparticles with methanol alone, but sodium citrate by itself can reduce AuCl3 at 60℃ to obtain a ruby(wine-red) color sols with an average size of 21 nm. Using both methanol and sodium citrate, stable purple-color sols can be obtained with a higher aspect ratio and the average size is around 35 nm. When the citrate concentration is increased, the sol color turns to dark-purple, the average particle increases, and the stability decreases.
In ORR tests, Au sols show a lower onset potential than Au disk electrode; the same phenomena is found when Pt black is compared to Pt disk. The per-gram electrocatalysis ORR activity of Au sols increases with decrease of particle size, but the aspect ratio did not show a significant influence on the ORR activity.
In CO oxidation tests, Pt catalysts show oxidation activity to both strongly adsorbed CO and CO dissolved in solution at 0.85-1.0 and 1.0-1.4 V respectively. The former current seems dependent on the CO concentration while the latter seems dependent on the surface hydroxyl concentration. Gold electrodes have a relatively weak CO oxidation at 1.05 V attributable to adsorbed CO, and oxidation currents attributable to solution phase CO at 1.23-1.36 V. The results indicate that Au nanoparticles are active for ORR and CO oxidation in acidic electrolyte but its activity is lower than Pt.

並列關鍵字

Au nanoparticle ； AuCl3 ； Rotating disk electrode ； H2SO4 ； Oxygen reduction reaction

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