Facile Synthesis of Nitrogen‐Doped Graphene Aerogels for Electrode Materials in Supercapacitors

Three‐dimensional porous nitrogen‐doped graphene aerogels (NGAs ) were synthesized by using graphene oxide (GO ) and chitosan (CS ) via a self‐assembly process by one‐pot hydrothermal method. The morphology and structure of the as‐prepared materials were characterized by means of scanning electron microscopy, transmission electron microscopy, X‐ray diffraction, XPS spectroscopy, Raman spectroscopy, nitrogen adsorption/desorption measurement and Fourier transform infrared spectroscopy. The electrochemical performance of NGAs was studied by cyclic voltammetry, galvanostatic charge/discharge and impedance spectroscopy measurements. The microstructure, surface area and capacitance of NGAs could be facilely controlled by adding different amounts of chitosan. The prepared NGA ‐4 showed a specific capacitance of 148.0 F/g at the discharge current density of 0.5 A/g and also retained 95.3% of the initial capacitance after 5000 cycles at the scan rate of 10 mV /s. It provided a possible way to obtain graphene based materials with high surface area and capacitance.     

Layer-by-layer engineered Co-Al hydroxide nanosheets/graphene multilayer films as flexible electrode for supercapacitor

Multilayer films of Co-Al layered double hydroxide nanosheets (Co-Al LDH-NS) and graphene oxide (GO) were fabricated through layer-by-layer (LBL) assembly. By using a three-electrode system, the electrochemical performances of the films were investigated to evaluate their potential as electrode materials to be used in flexible supercapacitor devices. The Co-Al LDH-NS/GO multilayer films exhibited a high specific capacitance of 880 F/g and area capacitance of 70 F/m(2) under the scan rate of 5 mV/s. And the film exhibited good cycle stability over 2000 cycles. After treating the films at 200 °C in H(2) atmosphere, the specific capacitance and area capacitance were largely increased up to 1204 F/g and 90 F/m(2) due to partial reduction of GO. A flexible electrode by depositing Co-Al LDH-NS/GO multilayer film onto PET substrate was prepared to show the potential of Co-Al LDH-NS/GO films for flexible energy storage.     

Ni3(HCOO)6/还原氧化石墨烯复合电极材料的制备及电容性能

以氧化石墨烯(GO)为前驱体, Ni(NO₃)₂·6H₂O为镍源, 甲酸为配体, N,N-二甲基甲酰胺为溶剂, 通过一步溶剂热法制备了Ni₃(HCOO)₆/rGO复合电极材料. 研究结果表明, 通过金属镍离子和配体在氧化石墨烯表面超分子自组装成核, 形成了“三明治”式的夹心复合结构; 不同的GO浓度对复合材料的物相结构、 晶体尺寸大小、 形貌及电化学性能有很大的影响; 当GO的浓度为8 mg/mL时, 在100 ℃下反应24 h得到的Ni₃(HCOO)₆/rGO复合材料在电解液为1 mol/L KOH, 5 mV/s下比电容高达940 F/g, 经过500次充放电循环后电容的保持率为96.28%.     

KOH activated carbon derived from biomass-banana fibers as an efficient negative electrode in high performance asymmetric supercapacitor

Here we demonstrate the fabrication, electrochemical performance and application of an asymmetric supercapacitor(AS) device constructed with β–Ni(OH)_2/MWCNTs as positive electrode and KOH activated honeycomb-like porous carbon(K-PC) derived from banana fibers as negative electrode. Initially,the electrochemical performance of hydrothermally synthesized β–Ni(OH)_2/MWCNTs nanocomposite and K-PC was studied in a three-electrode system using 1 M KOH. These materials exhibited a specific capacitance(Cs) of 1327 F/g and 324 F/g respectively at a scan rate of 10 m V/s. Further, the AS device i.e.,β–Ni(OH)_2/MWCNTs//K-PC in 1 M KOH solution, demonstrated a Cs of 156 F/g at scan rate of 10 m V/s in a broad cell voltage of 0–2.2 V. The device demonstrated a good rate capability by maintaining a Cs of 59 F/g even at high current density(25 A/g). The device also offered high energy density of 63 Wh/kg with maximum power density of 5.2 kW/kg. The AS device exhibited excellent cycle life with 100% capacitance retention at 5000 th cycle at a high current density of 25 A/g. Two AS devices connected in series were employed for powering a pair of LEDs of different colors and also a mini fan.     

Preparation and Pseudo-capacitance Performance of NiCo2O4 Nanosheets

Ternary nickel cobaltite(NiCo₂O₄), as a promising electrode material for supercapacitors, has attracted increasing attention for its excellent electrochemical properties. In this study, novel NiCo₂O₄ nanosheets were rationally designed and prepared using dealloying process, followed by an oxidation treatment. The as-prepared sample was characterized by microstructural and electrochemical techniques in view of its possible application in supercapacitors. The as-prepared sample exhibited high specific capacitance and excellent durability. The specific capacitance reached 663 F/g at 1 A/g and the rate capacitance high up to 73.6% when the current density increased from 1 A/g to 20 A/g. After 5000 cycles of galvanostatic charge-discharge durability test at 4 A/g, the capacity retention rate was 82.1%. The results indicate that versatile dealloying can be used to prepare robust electrode for supercapacitor application.     

Non-aqueous approach to the preparation of reduced graphene oxide/α-Ni(OH)2 hybrid composites and their high capacitance behavior

Reduced graphene oxide/α-Ni(OH)(2) composites present high electrochemical properties, with specific capacitance of 1215 F g(-1) at 5 mV s(-1) scan rate, since graphene as conductive matrix provides electronic conduction pathway.     

皱褶表面介孔镍钴硫化物微球的制备及其超电性能

通过一步水热法分别合成了α-NiS、Co₃S₄和CoNi₂S₄纳米介孔电极材料,并研究了其电化学性能。 X射线衍射(XRD)、扫描电子显微镜(SEM)和透射电子显微镜(TEM)研究表明,介孔硫化物是由单相纳米颗粒堆叠组装而成,其中二元系的CoNi₂S₄由纳米片自组装形成了具有皱褶表面的微球形貌。 电化学性能研究表明,二元系的CoNi₂S₄比α-NiS、Co₃S₄具有更高的比电容、更佳的倍率特性和优异的循环稳定性。 在扫描速率为5 mV/s时,CoNi₂S₄材料在6 mol/L KOH电解液中比电容高达1678.3 F/g,优于α-NiS (787.4 F/g)和Co₃S₄(1532.7 F/g),在扫描速率从5 mV/s增加到100 mV/s时,其电容保持率为45.8%,比α-NiS(30.2%)和Co₃S₄(29.3%)高出约15%。 在15A/g的电流密度下,经过900次循环充-放电后,二元系的CoNi₂S₄的电容仍保持在96.3%,库伦效率保持在94.3%左右,说明镍钴双金属硫化物具有优异的循环稳定性能和充放电可逆性。     

二氧化锰微米球制备及其于超级电容器的应用

利用KMnO4氧化MnCO3微米球前躯体制备MnO2微米球.X射线衍射(XRD)、扫描电子显微镜(SEM)、循环伏安(CV)法等测试表明:该MnO2微米球由弱结晶α-MnO2构成,粒径为0.5~2μm.测试样品的MnO2微米球载量为5 mg.cm-2时,在2 mol.L-1(NH4)2SO4溶液中表现出良好的电容性能:其于2 mV.s-1的扫速下比电容达到了135.6 F.g-1;即使是100 mV.s-1的高扫速,比电容仍保持为118.8 F.g-1.500次循环过程中充放电效率保持在87.8%以上.第500次循环的比电容为110.5 F.g-1.     

One-pot synthesis of CoO–ZnO/rGO supported on Ni foam for high-performance hybrid supercapacitor with greatly enhanced cycling stability

The high specific capacitance along with good cycling stability are crucial for practical applications of supercapacitors,which always demands high-performance and stable electrode materials.In this work,we report a series of ternary composites of CoO-ZnO with different fractions of reduced graphene oxide(rGO) synthesized by in-situ growth on nickel foam,named as CZG-1,2 and 3,respectively.This sort of binder-free electrodes presents excellent electrochemical properties as well as large capacitance due to their low electrical resistance and high oxygen vacancies.Particularly,the sample of CZG-2(CoO-ZnO/rGO 20 mg) in a nanoreticular structure shows the best electrochemical performance with a maximum specific capacitance of 1951.8 F/g(216.9 mAh/g) at a current intensity of 1 A/g.The CZG-2-based hybrid supercapacitor delivers a high energy density up to 45.9 Wh/kg at a high power density of 800 W/kg,and kept the capacitance retention of 90.1% over 5000 charge-discharge cycles.     

High voltage supercapacitors using hydrated graphene film in a neutral aqueous electrolyte

The potential stability windows of chemical converted graphene in different aqueous electrolyte solutions were investigated for the first time. Based on this result, a supercapacitor with a high voltage and long cycle-life was prepared with the hydrated graphene films in the neutral aqueous solution at the maximum voltage of 1.6 and even 1.8 V. The electrochemical performance of the obtained sample was systematically investigated by cyclic voltammetry, galvanostatic charge/discharge and electrochemical impedance spectroscopy. According to the cyclic voltammetry, hydrated graphene film can still retain rectangular shape at the high scan rate of 0.5 V/s in the neutral aqueous electrolyte. At a galvanostatic charge/discharge rate of 1 or 200 A/g, the specific capacitance of 202.3 or 138.1 F/g was delivered, respectively. Furthermore, the EIS results also confirm its fast neutral ion diffusion and high operating frequency of 9.34 Hz.     

N-doped honeycomb-like porous carbon towards high-performance supercapacitor

Biomass-derived porous carbon with developed pore structure is critical to achieving high performance electrode materials. In this work, we report a grape-based honeycomb-like porous carbon (GHPC) prepared by KOH activation and carbonization, followed by N-doping (NGHPC). The obtained NGHPC exhibits a unique honeycomb-like structure with hierarchically interconnected micro/mesopores, and high specific surface area of 1268 m²/g. As a supercapacitor electrode, the NGPHC electrode exhibits a remarkable specific capacitance of 275 F/g at 0.5 A/g in a three-electrode cell. Moreover, the NGHPC//NGHPC symmetric supercapacitor displays a high energy density of 12.6 Wh/kg, and excellent cycling stability of approximately 95.2% capacitance retention after 5000 cycles at 5 A/g. The excellent electrochemical performance of NGHPC is ascribed to its high specific surface area, honeycomb-like structure and high-content of pyrodinic-N (36.29%). It is believed that grape-based carbon materials show great potential as advanced electrode materials for supercapacitors.     

Synthesis,Characterization and Optoelectronic Property of Axial-Substituted Subphthalocyanines

Two novel substituted subphthalocyanines have been prepared introducing m-hydroxybenzoic acid and m-hydroxyphenylacetic acid into the axial position of bromo-subphthalocyanine. The compounds have been characterized by Fourier transform infrared (FT-IR), Nuclear Magnetic Resonance (NMR) and single-crystal X-rays diffraction (XRD) methods. Their photophysical properties show that the axial substitution results into a relatively higher fluorescence quantum efficiency (Φ_F=5.74 for m-hydroxybenzoic acid and 9.09 % for m-hydroxyphenylacetic acid) in comparison with that of the prototype compound, despite the almost negligible influence on the maximum absorption or the emission position. Moreover, the electrochemical behaviors show that the axial-substituted subphthalocyanines also exhibit enhanced specific capacitances of 395 F/g (m-hydroxybenzoic acid) and 362 F/g (m-hydroxyphenylacetic acid) compared with 342 F/g (the prototype) to the largest capacitance at the scan rate of 5 mV/s, and the significantly larger capacitance retentions of 83.6 % and 82.1 % versus 37.3 % upon density up to 3 A/g. These results show the potential of these axial-substituted subphthalocyanines in the use as organic photovoltaics and supercapacitors.     

Low cost,high performance supercapacitor electrode using coconut wastes: eco-friendly approach

Low cost, high performance supercapacitor electrodes were fabricated using coconut waste as precursor. Simple one step pyrolysis is adopted to get the spherical shaped particle where lignocellulosic nature of carbon converts into porous carbon nanospheres. Three types of coconut wastes, namely, coconut fiber(CF), coconut leaves(CL) and coconut stick(CS) have been studied and compared for their application in supercapacitors. Uniform spherical shape with particle size ranging from 30 to 60 nm for leaves and sticks and ~20 nm for fibers was obtained. The electrochemical properties of the porous carbon nanospheres were studied using cyclic voltammetry(CV), chronopotentiometry(CP) and electrochemical impedance spectroscopy(EIS). The porous carbon nanospheres derived from all the three biowaste samples show good electrochemical performance for supercapacitor application. Porous carbon nanospheres derived from coconut fiber exhibited maximum specific capacitance of 236 F/g followed by coconut stick and coconut leaves with 208 and 116 F/g respectively at a scan rate of 2 m V/s. Further impedance studies showed a charge transfer resistance of 4.9 for the porous carbon nanospheres derived from coconut fiber, while those from coconut leaves and coconut stick exhibited a slightly higher resistance of 6 and14.2, respectively. The simple eco-friendly approach we have demonstrated for synthesizing coconut waste based carbon nanospheres makes them excellent candidates for future, low-cost, energy storage devices.     

Fabrication of nanostructured iron-cobalt layered double hydroxide: An innovative approach for the facile synthesis

Studying semiconductive materials-based supercapacitors is significant for developing next-generation energy storage devices. However, the fabrication of a novel semiconductive material-based electrode with self-supporting design, flexible support, and nanoarchitecture is a challenge for the material researcher of 21st century. We present a facile method to fabricate three-dimensional (3D), porous, conductive electrodes based on semiconductive materials with high electrochemical performance. We fabricate the FeCo-LDH sample via hydrothermal route and decorate it on the flexible carbon cloth (CC) to get a flexible and self-supporting electrode. Textural, morphological, elemental, thermal, and functional group studies of the hydrothermally generated powder were performed using XRD, SEM, EDX, TGA, and FTIR methods. Well-known EIS, GCD, and CV tests were used to evaluate the electrochemical possessions of the FeCo-LDH/CC electrode. The performed electrochemical experiments indicated that our manufactured FeCo-LDH/CC electrode has an excellent specific capacity of 1041F/g at 0.5 A/g. Our self-supporting and flexible electrode has excellent cycle stability (it loses only 7.3 percent of its capacity after 5000 GCD cycles). It retains 79.2 percent of its capacitance when the current density increases from 0.5 A/g to 9 A/g. The superior electrochemical activity observed is attributed to the electrode's novel structure and logical design. According to the electrochemical experiment findings, our manufactured FeCo-LDH/CC electrode has great promise for practical applications in next-generation electrochemical capacitors.     

Hierarchical porous nanofibers of carbon@nickel oxide nanoparticles derived from polymer/block copolymer system

The triblock copolymer (PAA-b-PAN-b-PAA) is prepared by reversible addition-fragmentation chain-transfer polymerization, and then blended with polymer (PAN) and metal hydroxide (Ni(OH)₂) as a precursor for heat-treatment. A composite material of hierarchical porous nanofibers and nickel oxide nanoparticles (HPCF@NiO) is prepared by electrospinning combined with high-temperature carbonization. The effects of the ratio of PAA and PAA-b-PAN-b-PAA on the internal structure of nanofibers and their electrochemical properties as positive electrode materials are investigated. The experimental results show that when the ratio of PAA to PAA-b-PAN-b-PAA is 1.3 to 0.4, it has good pore structure and excellent electrochemical performance. At the current density of 1 A/g, the specific capacitance is 188.7 F/g and the potential window is −1 V to 0.37 V. The asymmetric supercapacitor assembled with activated carbon as the negative electrode materials has a specific capacitance of 21.2 F/g in 2 mol/L KOH and a capacitance retention of 85.7% after 12,500 cycles at different current density.     

Highly Stretchable and Conductive Hybrid Fibers for High-performance Fibrous Electrodes and All-solid-state Supercapacitors

The development of lightweight, flexible, and stretchable energy storage systems is essential for state-of-the-art electronic devices.We propose a new and broad strategy to fabricate a stretchable and conductive GO/CNTs-TPU fiber electrode by direct wet spinning, from which a flexible fibrous supercapacitor is fabricated. The fibrous electrode exhibits a high strength of 11.68 MPa, high conductivity of 342 S/cm, and high specific capacitances(21.8 mF/cm, 36.45 F/cm~3, and 95 F/g). The specific capacitance of the assembled all-solid-state hybrid fiber-shaped supercapacitor reaches 14.3 F/cm~3. After 5000 charge-discharge cycles, 97% of the capacitance of the hybrid supercapacitor is maintained. These high-strength electrochemical electrode materials could be potential candidates for applications in practical and large-scale energy storage systems and textile clothes.     

Facile synthesis of high electrical conductive CoP via solid-state synthetic routes for supercapacitors

Co-P precursor was prepared by a mechanical alloying method and then is controlled to synthesis of Co P phase through an annealing method. The optimal conditions of ball milling and annealing temperature are investigated. The Co P exhibits higher electrical conductivity than graphite and cobalt oxide, showing excellent pseudocapacitive properties due its high electrical conductivity which can result in a fast electron transfer in high rate charge–discharge possess. The as-obtained Co P electrode achieves a high specific capacitance of 447.5 F/g at 1 A/g, and displays an excellent rate capability as well as good cycling stability. Besides, the asymmetric supercapacitor(ASC) based on the Co P as the positive electrode and activated carbon(AC) as the negative electrode was assembled and displayed a high rate capability(60%of the capacitance is retained when the current density increased from 1 A/g to 12 A/g), excellent cycling stability(96.7% of the initial capacitance is retained after 5000 cycles), and a superior specific energy of19 Wh/kg at a power density of 350.8 W/kg. The results suggest that the Co P electrode materials have a great potential for developing high-performance electrochemical energy storage devices.     

Ni–Al composite hydroxides fabricated by cation–anion double hydrolysis method for high-performance supercapacitor

Chemical doping of nickel hydroxide with other cations(e.g. Al~(3+)) is an efficient way to enhance its electrochemical capacitive performances. Herein, a simple cation–anion(Ni~(2+)and AlO_2) double hydrolysis method was developed toward the synthesis of nickel–aluminum(Ni–Al) composite hydroxides. The obtained composite hydroxides possesses a porous structure, large surface area(121 m~2/g) and homogeneous element distribution. The electrochemical test shows that the obtained composite hydroxides exhibits a superior supercapacitive performances(specific capacitance of 1670F/g and rate capability of 87% from 0.5 A/g to 20 A/g) to doping-free nickel hydroxide(specific capacitance of 1227 F/g and rate capability of 47% from 0.5 A/g to 20 A/g). Moreover, the galvanostatic charge/discharge test displays that after 2000 cycles at large current density of 10 A/g, the composite hydroxides achieves a high capacitance retention of 98%, indicative of an excellent electrochemical cycleability.     

Ti/Ru0.1Ti0.1Sn0.8O2电极电容性能研究

低温热分解法制备Ti/Ru0.1Ti0.1Sn0.8O2.XRD表征该样品结构特性,循环伏安和恒流充放电测定电极性能.结果表明,Ti/Ru0.1Ti0.1Sn0.8O2物相属细小的金红石相,在20 mV/s扫速下该电极比电容达933F/g.1000次充放电循环后,比电容衰减23.6﹪,显示良好的循环稳定性和可逆性.     

氨气还原氮化法制备有序介孔TiN粉体及其电化学性能

以四氯化钛为原料,嵌段共聚物P123(PEO_(20)-PPO_(70)-PEO_(20))为模板剂,氰胺为稳定剂,采用非水解溶胶-凝胶法制备有序介孔TiO_2粉体,再经氨气还原氮化处理得到有序介孔TiN粉体.利用广角/小角X射线衍射、电子显微镜和N_2气吸-脱附等对TiN粉体的结构进行了表征,并通过循环伏安和充放电测试表征了电化学性能.结果显示,该粉体为高纯立方TiN相,呈球形颗粒状,具有有序介孔结构,比表面积高达97 m~2/g.在不同扫描速率下循环伏安曲线均呈类矩形,根据电流密度为50 m A/g时的恒流充放电(GCD)曲线计算比电容为233 F/g,且经2000次充放电循环后比容量仍保持90%以上,在功率密度为0.1 k W/kg时能量密度高达65 W·h·kg~(-1).