Energy storage mechanism and electrochemical performance of graphene/manganese dioxide composites
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摘要: 超级电容器因具有高功率密度、长使用寿命等优点备受关注,而电极材料是决定其电化学性能的主要因素。以氧化石墨烯(GO)为碳源,H2O2和KMnO4为MnO2的前驱体,通过一步水热法制备了石墨烯/二氧化锰复合材料(RGO/MnO2)。采用XRD、Raman和SEM对复合材料进行微观结构表征。结果表明,复合材料中球状MnO2分布于RGO片层上。分析了RGO/MnO2的储能机制,证明其储能过程主要是受表面电容控制。在5 mV·s−1时,表面电容占总电容的86.2%,当扫速增加到200 mV·s−1时,表面电容可以占到总电容的97.3%。为提高器件的能量密度,以RGO/MnO2为正极、RGO为负极,组装了RGO/MnO2//RGO非对称超级电容器(ASC)。在功率密度为100 W·kg−1时,其能量密度高达72.8 W·h·kg−1。Abstract: Supercapacitors have been attracted tremendous attention due to their high power density and long cycle life, etc. The electrode material is the main factor affecting electrochemical properties. Graphene/manganese dioxide composites (RGO/MnO2) were prepared using one pot hydrothermal method with graphene oxide (GO) as carbon source, as well as H2O2 and KMnO4 as MnO2 precursors. It was found that sphere-like MnO2 distributes on the graphene sheets by the microstructure tests. The energy storage mechanism of the composite was discussed. It displays that the reaction is the surface dominant process. The surface capacitance accounts for 86.2% of the total capacitance at 5 mV·s−1, While it can account for 97.3% at 200 mV·s−1. In order to assemble a device with high energy density, this work fabricated an asymmetric supercapacitor (ASC, RGO/MnO2//RGO) using the RGO/MnO2 as the positive electrode and RGO as the negative electrode, respectively, which exhibits high energy density (72.8 W·h·kg−1 at 100 W·kg−1).
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Key words:
- graphene /
- manganese dioxide /
- composites /
- energy storage mechanism /
- asymmetric supercapacitor
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图 3 RGO/MnO2对称超级电容器的循环伏安(CV)曲线 (a)、恒电流充放电(GCD)曲线 (b) 和交流阻抗(EIS)图 (c);RGO/MnO2和RGO对称超级电容器在不同电流密度下的比电容 (d) 和Ragone图 (e);RGO/MnO2对称超级电容器的循环性能图 (f)
Figure 3. Cyclic voltammetry (CV) curves (a) and constant current charge-discharge (GCD) profiles (b), electrochemical impedance spectroscopy (EIS) plot (c) of RGO/MnO2 symmetric supercapacitor; Specific capacitance at different current densities (d) and Ragone plot (e) of RGO/MnO2 and RGO symmetric supercapacitor; Cycle performance of RGO/MnO2 symmetric supercapacitor (f)
Rs—Ohmic resistance; Rct—Charge transfer resistance; W—Warbury impedance; C—Constant phase angle impedance
图 5 RGO/MnO2//RGO非对称超级电容器(ASC)的电化学性能:(a) 不同电压窗口下的CV曲线;(b) 扫速为10 mV·s−1时比电容随电压窗口增加的曲线;(c) CV曲线;(d) 不同扫速时的比电容;(e) GCD曲线;(f) 不同电流密度时的比电容
Figure 5. Electrochemical performance of asymmetric supercapacitor (ASC, RGO/MnO2//RGO): (a) CV curves measured with different potential windows; (b) Specific capacitances with the increase of potential windows at 10 mV·s−1; (c) CV curves; (d) Specific capacitance at various scan rates; (e) GCD profiles; (f) Specific capacitance at different current densities
表 1 不同扫速v下RGO/MnO2电极的总电容(C)、双电层电容(EDLC)和赝电容(PC)
Table 1. Total specific capacitance (C), electrical double layer capacitance (EDLC) and pseudo-capacitance (PC) of RGO/MnO2 electrodes at different scan rates v
Scan rate/(mV·s−1) 5 10 20 50 80 100 200 C/(F·g−1) 265.0 256.0 246.7 233.2 224.6 220.1 216.1 EDLC/(F·g−1) 228.4 230.1 228.4 221.6 215.4 211.9 210.3 PC/(F·g−1) 36.6 25.9 18.3 11.6 9.2 8.2 5.8 -
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