含氧化錳複合氣凝膠在超級電容器之應用

Applications of Manganese Oxide Containing Composite Aerogels in Supercapacitors

林佑勳(Yu-Hsun Lin)

指導教授 ： 呂世源

國立清華大學/工學院/化學工程學系/碩士(2010年)

摘要

本研究成功第一個採用非金屬烷氧化物為前驅物，經溶膠-凝膠法合成出氧化錳氣凝膠，經XRD鑑定圖譜可知其為hausmannite結構的Mn3O4晶相，其比表面積可達79m2/g。經300℃熱處理之氧化錳氣凝膠經循環伏安法測試，比電容值於掃描速率25mV/s、電解質為0.5 M Na2SO4溶液、操作電位0.1V~0.9V vs. Ag/AgCl下可達122F/g，其CV圖形接近矩形，呈現良好之電容可逆性。將不同熱處理溫度之氧化錳氣凝膠經過2000圈循環伏安法做長效性測試，比電容值最多衰退4%，顯示其擁有極佳之穩定長效性。
為了改善氧化錳氣凝膠較低的比表面積，本研究首先採用高比表面積之氧化錫氣凝膠(比表面積317m2/g)為骨架基底，於孔洞結構中，採電化學方式，成長氧化錳，作為超級電容之電極研究。當以氧化錫氣凝膠為骨架，定電位2V成長氧化錳之氧化錳/氧化錫氣凝膠複合電極，比電容值於上述相同之電容操作條件下可達253F/g，循環伏安圖形接近矩形，呈現極佳之電容可逆性。
為了改善骨架基底之導電性，進而採以高導電性(片電阻0.00148Ω/□)碳氣凝膠(比表面積577m2/g)為骨架，定電位1.5V成長氧化錳之氧化錳/碳氣凝膠複合電極，比電容值於上述之相同操作條件下可高達503F/g，經過六千圈長效穩定性測試，比電容值僅僅衰退0.99%，具備極佳之長效穩定性。利用超高掃描速率500mV/s做循環伏安測試，比電容值為243F/g，相較於25mV/s之比電容值，仍維持62.8%，且能保持極佳的可逆性，顯示以此電極作為超級電容時，於高速充放電的過程中，仍可維持極佳的比電容值與電容表現。除此之外，經EIS分析得知，此氧化錳/碳氣凝膠複合電極具有理想電容行為，並經循環伏安法計算，得知其提供了相當好的能量密度與功率密度，分別為21.6Wh/kg與48.5kW/kg，於下世代超級電容器之設計需求，提供了一個低成本，高效能之材料選擇。

關鍵字

超級電容器 ； 氧化錳 ； 氣凝膠

並列摘要

Manganese oxide aerogels were successfully synthesized with an epoxide addition procedure by using MnCl2‧4H2O as the precursor. The as-prepared aerogels possessed the crystalline phase of hausmannite of Mn3O4 and a BET specific surface area of 79m2/g. After heat treatment at 300 oC, the aerogels gave specific capacitances (SC) of up to 122F/g in 0.5M Na2SO4 solution, at a scan rate of 25mV/s, and within the window of 0.1~0.9V vs. Ag/AgCl. The resulting cyclic voltammetry (CV) loops appeared rectangular, implying high reversibility. After 2000 cycles of CV scans, the aerogels showed excellent cycle stability, retaining at least 96% of the maximum SC value.
In order to improve on the issue of low electrical conductivity of manganese oxides, tin oxide aerogels (317m2/g) and carbon aerogels (577m2/g) of high specific surface areas and better electrical conductivities were used as the porous template to accommodate the functioning manganese oxides. Manganese oxides were electrodeposited into the aerogel templates with a simple 2-electrode potentiostatic procedure operated at different potentials. These composite electrodes, possessing high electrical conductivity backbone and rich redox reactions of transition metal oxides were found promising for supercapacitors. The SC of the manganese oxide (deposited at 2V)/tin oxide aerogel composite electrode was 253F/g, a significant enhancement over that of the plain manganese oxide aerogel, mainly because of the enlarged specific surface area provided by the tin oxide aerogel template. To seek further improvement, carbon aerogels of high conductivity (0.00148Ω/□) and high surface area were used as the template for manganese oxides. The SC value of this MnOx/CA, with MnOx deposited at 1.5 V, was as high as 503F/g, and retained 99% of the maximum SC value after 6000 cycles of CV scans, indicating the further boost in SC and excellent cycle stability. The SC value of this composite electrode remained high at 243F/g even at a very high scan rate of 500mV/s, retaining 62.8% of the SC values obtained at a scan rate of 25mV/s, and achieving a high specific energy density of 21.6Wh/kg and a high specific power density of 48.5kW/kg. This work demonstrates the advantages of using composite electrodes for the next-generation supercapacitors.

並列關鍵字

supercapacitor ； manganese oxide ； aerogel

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