1 实验方法
1.1 实验用试剂和仪器
四水氯化锰、聚苯胺和氢氧化钾(均为分析纯)；氧化石墨；冷冻干燥机(FD-1A-50)；电化学工作站(CHI660E)；分析天平(EX125DZH)；超声波清洗机(SB-3200)；MBE数显鼓风干燥箱(GZX-9076)。
1.2 rGO/PANI/MnO2 的制备
在氧化石墨中加入适量的蒸馏水,超声2 h配成浓度为2 mg/mL的氧化石墨烯(GO)水溶液,将50 mL的GO水溶液分别放到三个小烧杯中,在其中分别加入99 mg、198 mg和396 mg的MnCl2·4H2O和50 mg的PANI。将这三份混合溶液搅拌均匀后分别转移到100毫升的反应釜中,在170℃水热反应24 h。然后用去离子水清洗,将其冻干制得rGO/PANI/MnO2三元复合材料。根据MnCl2·4H2O加入量的不同,将三个产物分别标记为rGO/PANI/MnO2 -1,rGO/PANI/MnO2-2,rGO/PANI/MnO2-3。为了比较,在GO水溶液中不添加PANI与MnCl2·4H2O而其它条件相同,制备石墨烯样品(rGO)。
1.3 结构和性能表征
用X射线衍射仪(XRD,Bruker D8 Advance)测定样品的结构,X射线放射源为Cu Kα射线,波长0.15406 nm,扫描范围为10°~80°(2θ),用X射线光电子能谱仪(ThermoFischer,ESCALAB 250Xi)测试样品的X射线光电子能谱(XPS),激发源采用Al Kα射线(hv=1486.6 eV),工作电压12.5 kV。用场发射扫描电子显微镜(SEM、Hitachi S4800/FEI NANOSEM 450)分析样品的形貌。
使用CHI660E电化学工作站利用双电极体系进行电化学性能测试。制备rGO/PANI/MnO2与rGO电极材料时无需添加导电剂与粘合剂,制备PANI电极时需加入炭黑和60%的聚四氟乙烯,三者质量比为80∶15∶5,然后用6 mol/L氢氧化钾溶液作为电解质,用两个相同的集流体泡沫镍电极组装超级电容器。
在对称超级电容器中,根据CP曲线计算电极的比电容(Ce)
式中m为活性物质的质量,Δt为放电时间,I为放电电流,ΔV为放电时的电压差。
以rGO/PANI/MnO2为阳极电极、rGO为阴极电极、6 mol/L KOH溶液为电解质,组装不对称超级电容器。为了保证阳极和阴极的电荷相等,负载在阳极和阴极上的活性物质质量为
不对称超级电容器的器件比电容(Ccell)、能量密度(E)和功率密度(P)分别为
其中I为放电电流,Δt为放电时间,m(m=m++m-)为活性物质的质量,ΔV为放电时的电压降。
2 结果和讨论
2.1 物相和结构
图1给出了反应物含量不同的rGO/PANI/MnO2三元复合材料以及GO与rGO的XRD谱。可以看出,在GO的谱中2θ=10.4°处有一个强的衍射峰,对应(002)晶面。根据Bragg方程计算出其晶面间距为0.848 nm。在rGO的XRD谱中有一个位于24.1°的宽衍射峰,而10.4°处的峰完全消失。这些结果表明,GO中大部分含氧官能团被去除,GO还原为rGO。值得注意的是,在rGO/PANI/MnO2三元复合材料的XRD谱中,衍射峰的峰位和峰形与rGO基本相同,都在24°处附近出现衍射峰,表明PANI和MnO2在水热过程中主要以无定形态沉积在石墨烯的网络结构中。
图1
图2给出了rGO/PANI/MnO2-3三元复合材料的XPS谱,在全谱图上出现了明显的C、O、N及Mn信号峰(图2a)。图2b、2c和2d分别给出了rGO/PANI/MnO2-3的Mn2p、N1s和C1sXPS谱。在Mn2p的XPS谱中642.1 eV和653.8 eV附近出现两个主峰(两峰间能量差11.7 eV),对应Mn2p3/2和Mn2p1/2的结合能,与文献报道的MnO2的峰值吻合较好[32],表明所得三元复合材料中有Mn(Ⅳ),也证明水热反应过程中生成了MnO2。C1s谱可分成三个不同的峰,分别位于284.8 eV(C-C/C=C),286 eV(C-N)和286.8 eV(C=O)。N1s谱图亦可拟合成3个峰,分别位于399.5 eV、401.5 eV和402.5 eV,对应吡啶-N、吡咯-N和石墨-N。
图2
图2
rGO/PANI/MnO2-3三元复合材料的XPS谱
Fig.2
XPS spectra of rGO/PANI/MnO2-3 (a) survey, (b) Mn2p, (c) N1s and (d) C1s
2.2 材料的形貌
图3给出了rGO/PANI/MnO2-3不同放大倍数的SEM照片,清晰可见石墨烯的三维网状结构。在合成复合材料的水热反应过程中,MnCl2·4H2O氧化为MnO2,与聚苯胺发生共沉积生成了无定形不规则的块状结构,原位生长在石墨烯的三维网状结构上。三维网状结构的石墨烯充当载体使制得的复合材料具有自支撑性能,而且本身作为网络导电体还提高了电极材料的导电性能。
图3
2.3 电化学性能
图4a给出了rGO、PANI与rGO/PANI/MnO2-3在2 mV/s时的CV曲线。可以看出,PANI的CV曲线有明显的氧化还原峰,说明其主要依靠赝电容储能,rGO的CV曲线呈矩形,说明其主要靠物理吸附储能,是双电层电容。另外,三元复合材料的CV曲线所包围的面积比另外两种单体rGO与PANI大,说明复合材料比rGO和PANI具有较高的比电容。其原因可能是复合材料的协同效应。这种复合材料不仅可阻止石墨烯团聚,还能提高材料整体的电容性能。
图4
图4
rGO、PANI与rGO/PANI/MnO2-3在扫速为2 mV/s下的CV曲线,rGO、PANI和rGO/PANI/MnO2-3在电流密度为0.2 A·g-1时的CP曲线以及rGO、PANI与rGO/PANI/MnO2-3的EIS图(插图表示高频区域的曲线)
Fig.4
CV curves of rGO、PANI and rGO/PANI/MnO2-3 at 2 mV/s (a), CP curves of rGO、PANI and rGO/PANI/MnO2-3 at 0.2 A·g-1 (b), EIS curve of rGO、PANI and rGO/PANI/MnO2-3 (c), and inset shows the high-frequency region of the plot
图4b给出了rGO、PANI与rGO/PANI/MnO2-3在电流密度为0.2 A·g-1时的CP曲线。可以看出,复合材料电极和rGO的CP曲线都具有良好的三角形对称性。这表明：它们具有良好的充放电可逆过程,体现出双电层电容器的储能行为。PANI的CP曲线不是等腰三角形,充放电过程出现平台,表明电极发生了氧化还原反应。还可看出,复合材料电极具有较长的放电时间。根据比电容
图5a给出了反应物含量不同的复合材料的CV曲线(扫描速度为2 mV/s)。可以看出,三条CV曲线都近似矩形,表明材料具有很好的电容特性。rGO/PANI/MnO2-3复合材料的CV曲线包围的面积最大,表明其具有较高的比电容。图5b给出了rGO/PANI/MnO2-3复合材料不同扫描速率的CV曲线。可以看出,CV曲线都呈矩形,表明其能快速充放电,具有优异的电化学性能。为了更好地理解三元复合材料的储能机理,详细研究了电荷存储过程。这种电极的电荷存储：包括电容控制部分(包括双电层电容和表面作用引起的赝电容)和扩散控制部分(基于扩散/插层的赝电容)[33]。根据不同扫描速率的CV曲线,电容贡献为[34]
图5
图5
三种复合材料在扫速为2 mV/s下的CV曲线,rGO/PANI/MnO2-3复合材料在不同扫描速率下的CV曲线和扫速为5 mV/s下的电容控制贡献以及 rGO/PANI/MnO2-3复合材料在不同扫速下的电容控制与扩散控制贡献率
Fig.5
CV curves of the three composites at 2 mV/s (a), CV curves of rGO/PANI/MnO2-3 at different scan rates (b), the capacitive contribution at a scan rate of 5 mV/s (c), the ratio of capacitive effects and diffusion controlled contributions at different scan rates (d)
其中I(mA)为固定电位下的电流,v(mV/s)为扫描速率,k1v和k2v1∕2 分别为电容贡献和扩散贡献。
图6a给出了反应物含量不同的复合材料在电流密度为0.2 A·g-1时的CP曲线。3种复合电极材料的CP曲线均呈现良好的三角形对称性,表明其均具有良好的可逆充放电和优异的电化学性能。根据比电容
图6
图6
三种复合材料在电流密度为0.2 A·g-1时的CP曲线,rGO/PANI/MnO2-3复合材料在不同电流密度下的CP曲线,rGO/PANI/MnO2-3复合材料Ce与电流密度的关系以及三种复合材料的EIS图
Fig.6
CP curves of the three composites at 0.2 A·g-1 (a), CP curves of rGO/PANI/MnO2-3 under different current densities (b), the relationships between Ce and current densities of rGO/PANI/MnO2-3 (c) and EIS curve of the three composites (d)
为了进一步提高三元复合材料的电化学性能,本文以rGO/PANI/MnO2-3为正极、rGO为负极、以6 mol/L KOH为电解液组装一种不对称电容器。图7a给出了不对称超级电容器在扫速为10 mV/s时不同电位窗口的CV曲线。可以看出,电位窗口为0~1.6 V时电极有轻微的极化。电位窗口继续增大到1.8 V时电流密度迅速增大,电极极化程度增大。这表明,这种不对称电容器的最大工作电位窗口为1.6 V。图7b材料不对称电容器的电位窗口为0~1.6 V时不同扫速的CV曲线。可以看出,扫描速度不同的CV曲线呈现矩形形状,表明这种不对称电容器具有良好的电容特性。图7c给出了不对称超级电容器在1 A·g-1时不同电位窗口下的CP曲线。可以看出,尽管电位窗口不同但是这些直流曲线均具有良好的三角形对称性,表明复合材料和rGO电极均具有良好的可逆充放电性能。图7d给出了不对称超级电容器在不同电流密度下的CP曲线。可以看出,随着电流密度的增大充放电时间逐渐变短,但是曲线仍为近似对称的三角形,表明其优异的电化学性能。图7e给出了能量密度(E)与功率密度(P)的关系。可以看出,功率密度为17.48 W·kg-1时能量密度可达13.5 Wh·kg-1。图7f给出了不对称电容器在0.5 A·g-1下器件容量保留值与循环次数的关系。可以看出,循环1000次后这种不对称电容器的容量为初始容量值的92.6,表明其具有良好的耐久性。
图7
图7
不对称超级电容器在扫速为10 mV/s时不同电位窗口的CV曲线,不同扫速的CV曲线,1 A·g-1时不同电位窗口下的CP曲线,在不同电流密度下的CP曲线,能量密度与功率密度的关系以及容量保留值与循环次数的关系
Fig.7
CV curves of asymmetric supercapacitor at different potential windows at 100 mV/s (a), CV curves of asymmetric supercapacitor at different scan rates (b), CP curves of asymmetric supercapacitor at different potential windows at 1 A·g-1 (c), CP curves of asymmetric supercapacitor under different current densities (d), Ragone plots of the energy density versus power density for asymmetric supercapacitors (e) and Cycling life of asymmetric supercapacitors at 0.5 A·g-1 (f)
3 结论
用水热合成法并结合冻干操作,可制备rGO/PANI/MnO2三元复合材料。这种复合材料具有自支撑特性,其中的离子快速转移和扩散的三维网络状结构使其电容性能大大提高,可用于制造超级电容器的电极。作为电极材料,比电容可达388 F·g-1(0.5 A·g-1),优于单纯的rGO(234 F·g-1)和PANI电极(176 F·g-1)。使用这种复合材料作为正极、rGO作为负极组装的不对称超级电容器,可在0~1.6 V可逆地循环,功率密度为17.48 W·kg-1时的最大能量密度可达13.5 Wh·kg-1。
参考文献
A high-performance sodium-ion hybrid capacitor constructed by metalorganic framework-derived anode and cathode materials
[J].
Three-dimensional porous carbon framework coated with one-dimensional nanostructured polyaniline nanowires composite for high performance supercapacitors
[J].
In this paper, three-dimensional (3D) porous carbon framework (CF) is prepared using commercial sponge as template and furfuryl alcohol (C5H6O2) as carbon source, through polymerizing and solidifying by oxalic acid (H2C2O4) followed by a carbonizing process at high temperature. Then, one-demensional (1D) polyaniline (PANI) nanowires are deposited on the CF substrate by a simple one-step electrodeposition method to obtain CF-PANI energy storage electrode. The CF-PANI maintains initial 3D porous structure as CF substrate with PANI layer, benefiting for the diffusion of electrolyte and the contact between active material and electrolyte. Besides, the carbon skeleton is surrounded by the PANI nanowires, which provide more transfer channels for electrons during the charge/discharge process. The loading mass of PANI on CF is as high as 21.3 mg cm(-3), and the gravimetric and volumetric capacitances reach 866 F g(-1) and 18.5 F cm(-3), respectively, at the scan rate of 2 mV s(-1). Moreover, the asymmetric supercapacitor based on CF-PANI as anode electrode and CF as cathode electrode exhibits a high energy density of 44Wh kg(-1) at the power density of 800 W kg(-1), indicating its promising applications as the electrode material for supercapacitors. (C) 2018 Elsevier B.V.
Blessing and curse: how a supercapacitor's large capacitance causes its slow charging
[J].
Pseudocapacitive Na-ion storage boosts high-rate and areal capacity of self-branched 2D layered metal chalcogenide nanoarrays
[J].
KOH activation of diatomite-templated carbon and its electrochemical property in supercapacitor
[J].
KOH活化硅藻土模板炭及其电化学性能研究
[J].以硅藻土为模板,糠醇为碳源,合成了模板炭材料,并用KOH活化制备多孔炭材料。利用XRD、拉曼光谱、SEM及N<sub>2</sub>吸附对其结构进行表征,并对比研究了活化前后炭材料的电化学性能。结果表明：活化后模板炭的无序度增加,电化学性能有显著的提高。在1 Ag<sup>-1</sup>的电流密度下,活化后的多孔炭比容量为45.0~69.2 Fg<sup>-1</sup>;在20 Ag<sup>-1</sup>充放电时,比电容保持率仍可达45%以上。说明活化后的多孔炭材料具有良好的电化学性能,是较好的双层电容器电极材料。
Graphene: Status and prospects
[J].Graphene is a wonder material with many superlatives to its name. It is the thinnest known material in the universe and the strongest ever measured. Its charge carriers exhibit giant intrinsic mobility, have zero effective mass, and can travel for micrometers without scattering at room temperature. Graphene can sustain current densities six orders of magnitude higher than that of copper, shows record thermal conductivity and stiffness, is impermeable to gases, and reconciles such conflicting qualities as brittleness and ductility. Electron transport in graphene is described by a Dirac-like equation, which allows the investigation of relativistic quantum phenomena in a benchtop experiment. This review analyzes recent trends in graphene research and applications, and attempts to identify future directions in which the field is likely to develop.
Laser Scribing of high-performance and flexible graphene-based electrochemical capacitors
[J].Although electrochemical capacitors (ECs), also known as supercapacitors or ultracapacitors, charge and discharge faster than batteries, they are still limited by low energy densities and slow rate capabilities. We used a standard LightScribe DVD optical drive to do the direct laser reduction of graphite oxide films to graphene. The produced films are mechanically robust, show high electrical conductivity (1738 siemens per meter) and specific surface area (1520 square meters per gram), and can thus be used directly as EC electrodes without the need for binders or current collectors, as is the case for conventional ECs. Devices made with these electrodes exhibit ultrahigh energy density values in different electrolytes while maintaining the high power density and excellent cycle stability of ECs. Moreover, these ECs maintain excellent electrochemical attributes under high mechanical stress and thus hold promise for high-power, flexible electronics.
Carbon-based supercapacitors produced by activation of graphene
[J].
Electrodeposited more-hydrophilic nano-nest polyaniline electrodes for supercapacitor application
[J].
Vacuum annealed MnO2 ultra-thin nanosheets with oxygen defects for high performance supercapacitors
[J].
Core-shell polyaniline functionalized carbon quantum dots for supercapacitor
[J].
Preparation and capacitance properties of polyaniline/carbon microcoil composites
[J].
聚苯胺/碳螺旋纤维复合材料的合成及其电容特性研究
[J],通过微乳聚合法合成了聚苯胺/螺旋碳纤维(PANI/ CMCs)复合材料.通过扫描电子显微镜和红外光谱对复合材料进行表征, 发现PANI与CMCs之间有化学键合作用, 且PANI的包覆使得CMCs表面变粗糙; 当氯仿与反应体系体积比为1∶24时, PANI的包覆量大, 嫁接状况好.通过恒流充放电法和循环伏安法对材料的电容性能进行表征, 发现复合材料的比电容量达134.8 Fg<sup>-1</sup>, 750次恒流充放电循环后比电容保持率达63.3%, 比电容量及循环稳定性均明显优于CMCs或PANI本身.
High-performance solid-state supercapacitors based on intrinsically conducting polyaniline/MWCNTs composite electrodes
[J].
Hierarchical nanocomposite that coupled nitrogen-doped graphene with aligned PANI cores arrays for high-performance supercapacitor
[J].
Transition of charge transport phenomena from 3D to 1D hopping at low temperatures in polyaniline/graphene composites
[J].
Effect of dopants on the energy storage performance of reduced graphene oxide/polyaniline nanocomposite
[J].
Bridging of adjacent graphene/polyaniline layers with polyaniline nanofibers for supercapacitor electrode materials
[J].
Solar reduced porous graphene incorporated within polyaniline network for high-performance supercapacitor electrode
[J].
Facile fabrication and energy storage analysis of graphene/PANI paper electrodes for supercapacitor application
[J].
Electrochemical properties of graphene nanosheets/polyaniline nanofibers composites as electrode for supercapacitors
[J].
Screen printable thin film supercapacitor device utilizing graphene/polyaniline inks
[J].
Fabrication of highly ordered polyaniline nanocore on pristine graphene for high-performance supercapacitor electrodes
[J].
Facile synthesis of Fe2O3 nano-dots@nitrogen-doped graphene for supercapacitor electrode with ultralong cycle life in KOH electrolyte
[J].
High-performance supercapacitors based on polyaniline-graphene nanocomposites: some approaches, challenges and opportunities
[J].
High rate capability electrode from a ternary composite of nanodiamonds/reduced graphene oxide@PANI for electrochemical capacitors
[J].
A simple one-step approach for preparing flexible rGO-MnO 2 electrode material
[J].
A simple route to prepare a Cu2O-CuO-GN nanohybrid for high-performance electrode materials
[J].
Synthesis of hierarchical sulfonated graphene/MnO2/polyaniline ternary composite and its improved electrochemical performance
[J].
Preparation and characterization of graphene/SnO2/polyaniline nano-composites
[J].
石墨烯/SnO2/聚苯胺纳米复合材料的制备与表征
[J].
Preparation of 3D MnO2/polyaniline/graphene hybrid material via interfacial polymerization as high-performance supercapacitor electrode
[J].
3D reduced graphene oxide/MnO2/polyaniline composite for high-performance supercapacitor
[J].
Manganese oxide thin film preparation by potentiostatic electrolyses and electrochromism
[J].
Covalent graphene-MOF hybrids for high-performance asymmetric supercapacitors
[J].
Ordered mesoporous α-MoO3 with iso-oriented nanocrystalline walls for thin-film pseudocapacitors
[J].Capacitive energy storage is distinguished from other types of electrochemical energy storage by short charging times and the ability to deliver significantly more power than batteries. A key limitation to this technology is its low energy density and for this reason there is considerable interest in exploring pseudocapacitive materials where faradaic mechanisms offer increased levels of energy storage. Here we show that the capacitive charge-storage properties of mesoporous films of iso-oriented alpha-MoO(3) are superior to those of either mesoporous amorphous material or non-porous crystalline MoO(3). Whereas both crystalline and amorphous mesoporous materials show redox pseudocapacitance, the iso-oriented layered crystalline domains enable lithium ions to be inserted into the van der Waals gaps of the alpha-MoO(3). We propose that this extra contribution arises from an intercalation pseudocapacitance, which occurs on the same timescale as redox pseudocapacitance. The result is increased charge-storage capacity without compromising charge/discharge kinetics in mesoporous crystalline MoO(3).
