奈米結構之Au/MnO2複合陰極觸媒材料; Nanostructured Au/MnO2 composites as cathode Materials for high efficiency metal-air battery

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Title:	奈米結構之Au/MnO2複合陰極觸媒材料;Nanostructured Au/MnO2 composites as cathode Materials for high efficiency metal-air battery
Authors:	李柏潔;Li,Po-Chieh
Contributors:	化學工程與材料工程學系
Keywords:	空氣電池;氧氣還原;二氧化錳;奈米金粒子;奈米結構;P123
Date:	2013-07-29
Issue Date:	2013-08-22 11:39:17 (UTC+8)
Publisher:	國立中央大學
Abstract:	本研究著重於金屬-空氣電池(Metal-Air battery)之陰極材料開發，藉由碳粉與α、β、γ相之二氧化錳的混合形成複合觸媒。以及利用P123界面活性劑增加觸媒表面積，使觸媒提升反應面積，進一步提升觸媒電化學效果。最後加入不同重量比例之具有良好氧氣還原反應(ORR)效果的奈米金粒子(Au NPs)，用以提升ORR觸媒反應效果。藉由二氧化錳本身之OER觸媒能力，以及透過奈米金粒子提升ORR之觸媒能力，使得本研究之複合觸媒具有OER與ORR的雙效性。本實驗以XC72碳粉、硫酸錳、過錳酸鉀為前驅物，在不同前驅物比例下透過迴流法(Reflux)來合成不同相(α、β、γ)之二氧化錳觸媒。二氧化錳具有便宜、低污染、兼具ORR與OER的觸媒效果等優點，是二次空氣電池觸媒很好的選擇。添加P123作為界面活性劑，使觸媒在合成時能均勻分散，並將前驅物中之硫酸錳的Mn2+離子包覆。經由過錳酸鉀氧化成二氧化錳均勻生長在碳粉之上，使觸媒分散均勻不團聚，並提升觸媒表面積。最後再加入不同重量比例(2：1、4：1、8：1、16：1)的奈米金粒子，提升觸媒之導電性與ORR觸媒能力。利用SEM、EDX與XRD鑑定二氧化錳的表面形貌、組成成份及相鑑定，發現α，β，γ相之二氧化錳均為棒狀(rod-like)結構；其重量組成約為碳粉65%、二氧化錳35%；XRD圖譜與標準卡號相符，證實合成之二氧化錳確實為α、β、γ相。並利用BET量測其表面積，三相中以α相二氧化錳與碳粉之複合觸媒的表面積最大(95.38 m2/g)，添加P123之後更提升至123.80 m2/g，證明P123確實提高了觸媒之表面積。將製備好的觸媒粉末利用刮刀塗佈技術均勻塗佈於碳紙上，將塗佈後的碳紙烘乾後即為空氣電極試片。將此電極試片藉由LSV與鋅空氣全電池測試，可發現不同相二氧化錳之觸媒效果依序為：α > γ > β。在LSV測試中，α相二氧化錳與碳粉之複合觸媒在-0.7 V下具有-17.4 mA/cm2之電流值，γ與β相分別為-14.6與-5.68 mA/cm2；加入奈米金粒子後各相觸媒電流值明顯提升且過電位下降，在奈米金粒子含量(4：1)下，α 、γ 、β電流值分別為-38.86、-31.64、-17.7 mA/cm2，比起未加奈米金粒子之觸媒的電流值高出兩倍之多。在鋅空氣全電池放電測試中，α 、γ 、β相二氧化錳與碳粉之複合觸媒在50 mA/cm2的電流下之放電電位分別為1.088 V、1.072 V、1.050 V；加入P123之後，α相二氧化錳與碳粉之複合觸媒在50 mA/cm2的電流下之放電電位提升至1.150 V；在添加P123且?雜奈米金粒子含量(2：1)下，20 mA/cm2的電流下之放電電位更高達1.304 V，證明在二氧化錳與碳粉之複合觸媒中?雜奈米金粒子對於空氣電池具有良好的催化效果，未來可適用於不同型式的金屬空氣電池中。 This research focuses on the development of air cathodes for metal-air batteries. We synthesized composite catalytic materials to enhance the battery performance, especially for secondary metal-air battery applications due to bifunctional air cathode. The composite catalytic materials are composed of XC72 carbon black, α-、β- or γ-MnO2 and different weight ratio of gold nanoparticles (Au NPs), as the catalytic layer in the air cathode. By using P123 as a structure-directing reagent, the morphologies and the specific surface area of this composite material can be further tuned. Their morphologies、crystalline phase、surface area and electrochemical performance were characterized by SEM、XRD、BET and Potentiostat. The morphologies of α-、β- and γ-MnO2 are rod-like and the XRD patterns are consistent with JCPD cards. The BET surface area of α-、β- and γ-MnO2/XC72 are 95.38、73.03 and 85.76 m2/g, respectively The surface area of α-MnO2/XC72 increased from 95.38 m2/g to 123.8 m2/g by adding P123. It was found that the electrochemical performance of α-MnO2 was the best as air electrode. LSV measurements indicated that the current density of α-MnO2/XC72 was -17.4 mA/cm2 at -0.7 V, whereas β- and γ-MnO2/XC72 were -14.6 and -5.68 mA/cm2 at the same bias. Meanwhile, gold nanoparticles as additives increased the cathodic current density and lowered the overpotential. The current density of α-、β- and γ-MnO2/XC72 were -38.86、-17.7 and -31.64 mA/cm2 at -0.7 V by adding gold nanoparticles (weight ratio 4 : 1), respectively. Zn-air battery discharge test showed that the discharge voltages of α-MnO2, β-MnO2 and γ-MnO2/XC72 were 1.088 V, are 1.050 and 1.072 V at 50 mA/cm2, respectively. The discharge voltage of α-MnO2/XC72 increased to 1.15 V at 50 mA/cm2 by adding P123, perhaps due to the increase in specific surface area. The highest discharge voltage of α-MnO2/XC72 is 1.243 V at 50 mA/cm2 by adding P123 and Au nanoparticles (weight ratio 2：1). It is evident that this composite air cathode, MnO2/Au NPs, provides good catalytic activities, which could be a good candidate for various types of metal air battery in the future.
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