热处理对二氧化锰电化学行为的影响

热处理对二氧化锰电化学行为的影响

米娟;王玉婷;高鹏程;李文翠

【摘 要】以高锰酸钾和醋酸锰为前驱体,通过液相沉淀法合成得到二氧化锰.在不同温度热处理条件下研究二氧化锰的结构转变及其作为超级电容器电极材料的电化学行为.采用X射线衍射(XRD),扫描电镜(SEM),氮气物理吸附和热重(TG)等手段表征产物的结构特点;采用循环伏安和恒流充放电等方法表征其电化学行为.结果表明:合成的二氧化锰是具有中孔特征的α-MnO2,比表面积为253 m2·g-1,颗粒尺寸在50-100 nm之间.350℃以下的低温热处理使氧化锰仍能保持α-MnO2的晶体结构,比表面积为170 m2·g-1左右,单电极比电容值由原来未热解时的267 F·g-1增加到250℃热处理后的286 F·g-1.高温热处理(＞450℃)导致氧化锰逐渐过渡为α-Mn2O3,且表面积下降约为30 m2g-1,比电容急剧下降.低温热处理后氧化锰的电化学稳定性明显提高,在50 mV·s-1的快速扫描速率下,电极具有良好的倍率特性.%Manganese dioxide (MnO2) was synthesized using a fluid phase

method with potassium permanganate and manganous acetate as

precursors. The obtained MnO2 was treated thermally at different

temperatures. The structural transformation of MnO2, its electrochemical

behavior as an electrode material for use in a supercapacitor were

investigated by X-ray diffraction (XRD), scanning electron microscopy

(SEM), N2 physical adsorption, thermogravimetry (TG), cyclic voltammetry,

and galvanostastic charge-discharge. The results indicate that the

synthesized MnO2 can be assigned to its α phase and that it possesses a

mesoporous feature with a high surface area of up to 253 m2· g-1. After a

low temperature thermal treatment (＜350 ℃), the manganese oxide retained its α-MnO2 crystal structure and its specific surface area was

found to be approximately 170 m2· g-1. The specific capacitance of the

single electrode increased from 267 F· g-1 for untreated MnO2 to 286 F· g-1 for the sample treated at 250 ℃. However, high temperature thermal

treatment (＞450 ℃) results in a transformation of the manganese oxide

structure to α-Mn2O3 and then to α-Mn3O4. Additionally, the surface area

reduced to ca 30 m2· g-1 and this lead to a dramatic decrease in the

specific capacitance of manganese oxide. The electrochemical cycling

stability of manganese oxide improved noticeably after low temperature

thermal treatment and the electrode retained a good rate performance at

a scan rate of 50 mV·s-1.

【期刊名称】《物理化学学报》

【年(卷),期】2011(027)004

【总页数】7页(P893-899)

【关键词】二氧化锰;超级电容器;电极材料;热处理

【作 者】米娟;王玉婷;高鹏程;李文翠

【作者单位】大连理工大学化工学院,辽宁大连116024;大连理工大学化工学院,辽宁大连116024;大连理工大学化工学院,辽宁大连116024;大连理工大学化工学院,辽宁大连116024

【正文语种】中 文

【中图分类】O646 Abstract: Manganese dioxide(MnO2)was synthesized using a fluid phase

method with potassium permanganate and manganous acetate as

precursors.The obtained MnO2was treated thermally at different

temperatures.The structural transformation of MnO2,its electrochemical

behavior as an electrode material for use in a supercapacitor were

investigated by X-ray diffraction(XRD),scanning electron

microscopy(SEM),N2physical adsorption,thermogravimetry(TG),cyclic

voltammetry,and galvanostastic charge-discharge.The results indicate that

the synthesized MnO2can be assigned to its α phase and that it possesses

a mesoporous feature with a high surface area of up to 253 m2·g-1.After a

low temperature thermal treatment(<350 °C),the manganese oxide

retained its α-MnO2crystal structure and its specific surface area was

found to be approximately 170 m2·g-1.The specific capacitance of the

single electrode increased from 267 F·g-1for untreated MnO2to 286 F·g-1for the sample treated at 250 °C.However,high temperature thermal

treatment(>450°C)results in a transformation of the manganese oxide

structure to α-Mn2O3and then to α-Mn3O4.Additionally,the surface area

reduced to ca 30 m2·g-1and this lead to a dramatic decrease in the specific

capacitance of manganese oxide.The electrochemical cycling stability of

manganese oxide improved noticeably after low temperature thermal

treatment and the electrode retained a good rate performance at a scan

rate of 50 mV·s-1.

Key Words:Manganese dioxide;Supercapacitor;Electrode material;Thermal

treatment 超级电容器是一种高效能量转换和储存设备,可满足高功率脉冲或瞬时功率保持等应用需求.1当前,为提高超级电容器的工作电压和比能量,扩展其应用范围,人们对混合型超级电容器的研究表现出极大兴趣.从环保和经济的角度出发,制备高能量密度水相混合型超级电容器是电化学学科前沿之一.

通常混合型电容器的正负极分别由能产生法拉第赝电容的氧化物和多孔炭组成,利用过电势互补,可提高工作电压范围,从而提高能量密度.正极材料以导电聚合物和金属氧化物等赝电容材料为主.2其中过渡金属氧化物电极材料主要有氧化钌、氧化钴、氧化镍和氧化锰等,有研究表明,RuO2·xH2O的比电容高达760 F·g-1.3但由于RuO2价格昂贵,限制了它的实际应用,氧化镍和氧化钴的工作电位窗口过窄,也不利于材料在电容器方面的应用.氧化锰价廉易得,性能优良,环境友好,从而引起广大科研工作者的关注.Brousse等4在以MnO2为正极,活性炭(AC)为负极组成的不对称水相电解液体系中可获得2.0 V较稳定工作电压.将MnO2应用于超级电容器的阳极材料,一方面可以拓宽电势窗口,另一方面可以提供赝电容,从而提高电容器的能量密度和功率密度.

MnO2的赝电容储能机理主要依赖Mn(IV)到Mn(III)的还原反应来储存电荷,其理论电容值可达1233 F·g-1.5,6但在文献7-10中报道的MnO2颗粒的比电容值仅为100 F·g-1,而MnO2膜的电容值可达到700 F·g-1.可见,调变MnO2的结构可以显著提高其比电容值.MnO2的比电容值主要由其织构参数、晶形结构、电子离子传导率和电极材料/集流体的界面性质等参数决定.不同的制备方法又决定了其不同的晶形结构和形貌参数,即使对同一合成方法,通过控制不同的反应条件和参数可获得不同晶型的MnO2.液相沉淀法是应用最广泛的制备MnO2的方法,但合成的样品直接作为电极材料其电化学稳定性不好,库仑效率不高,不能满足对电容器快速充放电的应用要求.为克服这一问题,本文采用室温液相沉淀法制备MnO2,重点研究热处理对MnO2的晶形结构和电化学行为的影响,发现低温热处理在不改变MnO2