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.     

MnO2-directed synthesis of NiFe-LDH@FeOOH nanosheeet arrays for supercapacitor negative electrode

The complex-architectured NiFe-LDH@FeOOH negative material was first prepared by simple two-step hydrothermal method. In this study, the porous nanostructure of FeOOH nanosheets features a large number of accessible channels to electroactive sites and the two-dimensional layered structure of NiFe-LDH nanosheets have an open spatial structure with high specific surface area, which enhance the diffusion of ions in the active material. Benefited from above advantages, the excellent electrochemical properties were demonstrated. NiFe-LDH@FeOOH nanocomposites present high specific capacitance (1195 F/g at a current density of 1 A/g), lower resistance and well cycling performance (90.36% retention after 1000 cycles). Furthermore, the NiFe-LDH@MnO₂//NiFe-LDH@FeOOH supercapacitor exhibits 22.68 Wh/kg energy density at 750 W/kg power density, demonstrating potential application in energy storage devices.     

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.     

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.     

氮掺杂石墨烯量子点/MOF衍生多孔碳纳米片构筑高性能超级电容器

首先采用溶液法在碳布上生长Co-MOF二维纳米片,通过高温退火和刻蚀后得到MOF衍生多孔碳纳米片。以Co-MOF衍生的多孔碳纳米片/碳布(CNS/CC)作为碳基骨架,采用电化学沉积法负载高活性氮掺杂石墨烯量子点(N-GQDs),制备得到分级多孔结构的N-GQD/CNS/CC复合材料。组装成自支撑且无粘结剂的N-GQD/CNS/CC电极,当电流密度为1 A·g~(-1)时,其比电容高达423 F·g~(-1)。通过储能机制和电容贡献机制的研究表明,在碳纤维上原位生长的具有高双电层电容的CNS和表面负载具有高赝电容的N-GQDs之间相互协同作用,使得N-GQD/CNS/CC电极具有高电容性能,是一种理想的超级电容器电极材料。电极材料的高导电、分级多孔结构有利于电子的传输和电解质离子的扩散,具有良好的动力学性能,能快速充放电和具有优异的倍率特性。将电极组装成对称型超级电容器,功率密度为250 W·kg~(-1)时对应的能量密度达到7.9 Wh·kg~(-1),且经过10 000次循环后电容保持率为91.2%,说明氮掺杂石墨烯量子点/MOF衍生多孔碳纳米片复合材料是一种电化学性能稳定的具有高电容性能的全碳电极材料。     

基于聚多巴胺的氮掺杂碳材料的制备及其电化学性能

多孔碳材料由于高的比表面积、优异的电子传导率、良好的化学稳定性等优点在超级电容器电极材料领域被广泛研究。 碳材料的组成及表面孔结构直接影响其电化学性能,为进一步提高碳材料的电容性能,本文首次以聚多巴胺球为前体,KOH为活化剂,通过高温碳化成功制备了良好电化学性能的氮掺杂多孔碳材料。 通过扫描电子显微镜(SEM)、透射电子显微镜(TEM)、 X射线粉末衍射(XRD)、傅里叶变换红外光谱(FT-IR)、X射线光电子能谱(XPS)和Raman光谱等对所制备的氮掺杂多孔碳材料进行了形貌及结构组成的表征。 在6 mol/L KOH电解液中, 采用循环伏安、恒电流充放电对多孔碳材料的电化学性能进行了研究。 结果表明,由于双电层电容和赝电容的协同作用,在电流密度为1 A/g时,材料的比电容可达269 F/g,充放电循环1000圈后电容仍可保留初始值的93.5%。     

镍钴氢氧化物的制备及其电化学性能

采用化学共沉淀法成功制备了片状镍钴氢氧化物,并探究了不同镍钴物质的量比对样品形貌及电化学性能的影响。通过X射线衍射(XRD)、扫描电子显微镜(SEM)、X射线光电子能谱仪(XPS)及比表面积孔径分析仪(BET)对样品的结构、形貌进行了表征,并利用循环伏安法、恒电流充放电法等对其电化学性能进行了分析。结果表明,n(Ni)∶n(Co)=4∶1的样品直接用作电极材料时,具有最好的电化学性能:在0.5 A/g的电流密度下拥有1852 F/g的高比容量;电流密度增大20倍时,仍拥有1330 F/g的高比容量。以镍钴氢氧化物为正极,活性炭为负极组装的非对称式超级电容器在346 W/kg的功率密度下,能量密度达52 Wh/kg,在循环10000圈之后电容保持率为92%。优异的电化学性能表明,片状镍钴氢氧化物是很有应用潜力的电极材料之一。     

基于NiCo2O4纳米片电极的非对称混合电容器

The looming global energy crisis and ever-increasing energy demands have catalyzed the development of renewable energy storage systems. In this regard, supercapacitors (SCs) have attracted widespread attention because of their advantageous attributes such as high power density, excellent cycle stability, and environmental friendliness. However, SCs exhibit low energy density and it is important to optimize electrode materials to improve the overall performance of these devices. Among the various electrode materials available, spinel nickel cobaltate (NiCo₂O₄) is particularly interesting because of its excellent theoretical capacitance. Based on the understanding that the performances of the electrode materials strongly depend on their morphologies and structures, in this study, we successfully synthesized NiCo₂O₄ nanosheets on Ni foam via a simple hydrothermal route followed by calcination. The structures and morphologies of the as-synthesized products were characterized by X-ray diffraction, scanning electron microscopy, and Brunauer-Emmett-Teller (BET) surface area analysis, and the results showed that they were uniformly distributed on the Ni foam support. The surface chemical states of the elements in the samples were identified by X-ray photoelectron spectroscopy. The as-synthesized NiCo₂O₄ products were then tested as cathode materials for supercapacitors in a traditional three-electrode system. The electrochemical performances of the NiCo₂O₄ electrode materials were studied and the area capacitance was found to be 1.26 C·cm^-2 at a current density of 1 mA·cm^-2. Furthermore, outstanding cycling stability with 97.6% retention of the initial discharge capacitance after 10000 cycles and excellent rate performance (67.5% capacitance retention with the current density from 1 to 14 mA·cm^-2) were achieved. It was found that the Ni foam supporting the NiCo₂O₄ nanosheets increased the conductivity of the electrode materials. However, it is worth noting that the contribution of nickel foam to the areal capacitance of the electrode materials was almost zero during the charge and discharge processes. To further investigate the practical application of the as-synthesized NiCo₂O₄ nanosheets-based electrode, a device was assembled with the as-prepared samples as the positive electrode and active carbon (AC) as the negative electrode. The assembled supercapacitor showed energy densities of 0.14 and 0.09 Wh·cm^-3 at 1.56 and 4.5 W·cm^-3, respectively. Furthermore, it was able to maintain 95% of its initial specific capacitance after 10000 cycles. The excellent electrochemical performance of the NiCo₂O₄ nanosheets could be ascribed to their unique spatial structure composed of interconnected ultrathin nanosheets, which facilitated electron transportation and ion penetration, suggesting their potential applications as electrode materials for high performance supercapacitors. The present synthetic route can be extended to other ternary transition metal oxides/sulfides for future energy storage devices and systems.     

Facile SILAR Processed Bi2S3:PbS Solid Solution on MWCNTs for High‐performance Electrochemical Supercapacitor

Carbon based composite materials have gained much attention because of fulfilling desirable properties for supercapacitor application. In the featured work, the thin film of Bi₂S₃:PbS solid solution has been synthesized on multi‐walled carbon nanotubes (MWCNTs) by simple successive ionic layer adsorption and reaction (SILAR) method. The nanoparticle morphology provides sufficient electroactive channels for electrolyte ions to penetrate during electrochemical activities. The composite exhibits superior specific capacitance 676 F/g at constant specific current density of 5.56 A/g with fast charge‐discharge cycles. In association of energy storage characteristics, the fabricated symmetric cell exhibits excellent energy density of 13.36 Wh/kg by acquiring power density of 0.83 kW/kg. The superior results of the hybrid electrode promise a novel direction for high performance supercapacitor application.     

Green synthesis of graphene nanosheets/ZnO composites and electrochemical properties

A green and facile approach was demonstrated to prepare graphene nanosheets/ZnO (GNS/ZnO) composites for supercapacitor materials. Glucose, as a reducing agent, and exfoliated graphite oxide (GO), as precursor, were used to synthesize GNS, then ZnO directly grew onto conducting graphene nanosheets as electrode materials. The small ZnO particles successfully anchored onto graphene sheets as spacers to keep the neighboring sheets separate. The electrochemical performances of these electrodes were analyzed by cyclic voltammetry, electrochemical impedance spectrometry and chronopotentiometry. Results showed that the GNS/ZnO composites displayed superior capacitive performance with large capacitance (62.2 F/g), excellent cyclic performance, and maximum power density (8.1 kW/kg) as compared with pure graphene electrodes. Our investigation highlight the importance of anchoring of small ZnO particles on graphene sheets for maximum utilization of electrochemically active ZnO and graphene for energy storage application in supercapacitors.     

Nitrogen-doped porous carbon coated on MnCo2O4 nanospheres as electrode materials for high-performance asymmetric supercapacitors

Spinel-based nanostructured materials are commonly used as promising electrode materials for supercapacitor applications. The combination of heteroatom-doped carbon material with spinel oxides substantially improves the specific capacitance and cyclic stability. In this work, dopamine-derived nitrogen-doped carbon was coated on spinel phase MnCo₂O₄ nanospheres using simple solvothermal and calcination methods. Surface morphology and the crystalline structure of the prepared MnCo₂O₄@Nitrogen-doped carbon were confirmed by FESEM and X-ray diffraction. The electrochemical performance of MnCo₂O₄@Nitrogen-doped carbon electrode material was analyzed by cyclic voltammetry, galvanostatic charge–discharge, and electrochemical impedance spectroscopy techniques. MnCo₂O₄@nitrogen-doped carbon exhibits the highest specific capacitance of 1200 F/g compared to MnCo₂O₄ spheres are 726 F/g at 1 A/g and exhibits excellent cyclic stability (capacitance retention of 87% at 7 A/g after 3000 cycles). The enhanced performance of the composite might be benefitted from the synergistic effect between nitrogen-doped carbon on porous MnCo₂O₄ spheres. Furthermore, an asymmetric supercapacitor device was fabricated by using the optimized composition of MnCo₂O₄@NC-2 as a positive electrode and nitrogen, sulfur-doped reduced graphene oxide (NS-rGO) as a negative electrode, respectively. This asymmetric supercapacitor device achieves a maximum energy density of 61.0 Wh/kg at a power density of 2889 W/kg and possesses excellent capacitance retention of 95% after 5000 cycles at 7 A/g.     

Synthesis of vanadium oxides nanosheets as anode material for asymmetric supercapacitor

Vanadium oxides (V₂O₅) have been intensely investigated for advanced supercapacitors due to its extensive multifunctional properties of typical layered structure and multiple stable oxide states of vanadium in its oxides. In this study, V₂O₅ nanosheets are synthesized via V₂O₅ xerogel solvothermal reaction in ethanol solvent at 200 °C for 12 h. The V₂O₅ nanosheets facilitate the easy accessibility of ions and can provide more area available for electrochemical reactions. We have achieved the highest specific capacitance of 298 F/g and good rate discharge for V₂O₅ electrodes. Notably, the capacitance still retains a high retention rate of 85% after 10,000 cycles at 200 mV/s. Furthermore, asymmetric supercapacitors is assembled based on V₂O₅ nanosheets and active carbon electrode, and a specific capacitance of 13.2 F/g is obtained at 1 A/g, with a energy density of 4.7 Wh/kg at a power density of 0.798 kW/kg and remains 2.28 Wh/kg at 7.992 kW/kg. Based on these results, the asymmetric supercapacitor exhibits a good cycle life with 77.3% capacitance retention after 3000 cycles. It suggests that the V₂O₅ nanosheets are promising electrode material for electrochemical supercapacitors.     

萘基相互连接的多孔碳纳米囊的制备及超电容性能

以萘为碳源, 采用MgO模板诱导耦合KOH裁剪技术制备了相互连接的多孔碳纳米囊(ICNC). 结果表明所制备的ICNC₂具有大的比表面积(1811 m²/g)、 高的压实密度(1.38 g/cm³)和微孔孔容含量(58.93%). 在对称的超级电容器(SC)中, ICNC₂电极的体积比容在不同电流密度下分别高达420.8 F/cm³(0.069 A/cm³)和315 F/cm³(27.6 A/cm³), 容量保持率为74.82%. 在38 W/L功率密度下, ICNC₂基SC的体积能量密度为14.6 W?h/L. 经过20000次循环后, 其体积比容仅衰减1.4%, 库伦效率为99.1%, 为从萘基小分子制备储能用功能碳材料提供了一种可行的方法.     

Flexible asymmetric supercapacitor based on MnO2 honeycomb structure

By controlling the electroplating time of solution containing Mn(Ac)₂, the MnO₂ nanosheets were self-assembled to the honeycomb structure and showed an excellent electrochemical performance in 1 mol/L Na₂SO₄ electrolyte. Via pairing with activated carbon as negative electrode, the capacitor could deliver a maximum energy density of 43.84 Wh/kg and a maximum power density of 6.62 kW/kg.     

Design and Preparation of Graphene/Fe2O3 Nanocomposite as Negative Material for Supercapacitor

The development of high specific capacitance electrode materials with high efficiency, scalability and economic feasibility is significant for the application of supercapacitors, however, the synthesis of electrode material still faces huge challenges. Herein, graphene(G)/Fe₂O₃ nanocomposite was prepared via a simple hydrothermal method connected with subsequent thermal reduction process. Scanning electron microscopy(SEM) and transmission electron microscopy(TEM) results showed rod-like Fe₂O₃ nanoparticles were prepared and well-dispersed on graphene layers, providing a rich active site and effectively buffering the aggregation of Fe₂O₃ nanoparticles in the process of electrochemical reaction. The specific capacitance of the obtained G/Fe₂O₃ nanocomposite as negative electrode for supercapacitor was 378.7 F/g at the current density of 1.5 A/g, and the specific capacitance retention was 88.76% after 3000 cycles. Furthermore, the asymmetric supercapacitor(ASC) was fabricated with G/Fe₂O₃ nanocomposite as negative electrode, graphene as positive electrode, which achieved a high energy density of 64.09 W∙h/kg at a power density of 800.01 W/kg, maintained 30.07 W∙h/kg at a power density of 8004.89 W/kg, and retained its initial capacitance by 78.04% after 3000 cycles. The excellent result offered a promising way for the G/Fe₂O₃ nanocomposite to be applied in high energy density storage systems.     

Flexible CuCo2O4@Ni-Co-S hybrids as electrode materials for high-performance energy storage devices

Rational design of electrode meterials with unique core-shell nanostructures is of great significance for improving the electrochemical performance of supercapacitors. In this work, we prepare several CuCo₂O₄ @Ni-Co-S composite electrodes by a controllable hydrothermal and electrodeposition route. One-dimensional nanowires can shorten the ions transport path, while two-dimensional nanosheets expose many active sites. This enables three-dimensional structured composite with high electrochemical activity. The as-prepared heterostructured materials show a specific of 1048 C/g at 1 A/g. It still maintains 75.6% of initial capacity after 20000 cycles at 10 A/g. The device delivers an energy density of 79.2 Wh/kg when the power density reaches to 2280 W/kg. Moreover, it possesses an excellent mechanical stability after repeated folding at different angles     

Exfoliated graphite nanosheets/carbon nanotubes hybrid materials for superior performance supercapacitors

Nanostructured hybrid material of exfoliated graphite nanosheets and carbon nanotubes (GNSNT) served as supercapacitor electrode materials was presented. The nanostructured hybrid was prepared by a facile chemical reduction method. The hybrid material was characterized by X-ray diffraction technique, transmission electron microscopy, scanning electron microscopy, cyclic voltammetry, galvanostatic charge/discharge cycling, and four-point probe conductivity measurement to represent a well-defined nanostructure possessing a vast number of active sites and delivering the ingredients for a fast effective charge separation network. Our results clearly demonstrated that the hybrid possess a superior performance. A specific capacitance value 266 F/g was obtained for GNSNT hybrid electrode at a current density of 0.1 A/g, while it was only 185 F/g for exfoliated graphite nanosheets (GNS). At a higher current density of 2 A/g, the GNSNT electrode still keeps a specific capacitance of 220 F/g, which is more than double that of GNS. This synergistic effect of the nanostructured hybrid material offers an effective network for charge separation and therefore renders a significantly enhanced specific capacitance and rate capability.     

Electrodeposited NiSe_2 on carbon fiber cloth as a flexible electrode for high-performance supercapacitors

A flexible electrode of nickel diselenide/carbon fiber cloth(NiSe_2/CFC) is fabricated at room temperature by a simple and efficient electrodeposition method. Owing to NiSe_2 character of nanostructure and high conductivity, the as-synthesized electrodes possess perfect pseudocapacitive property with high specific capacitance and excellent rate capability. In three-electrode system, the electrode specific capacitance of the NiSe_2/CFC electrode varies from 1058 F g~(-1) to 996.3 F g~(-1) at 2 A g~(-1) to 10 A g~(-1) respectively, which shows great rate capability. Moreover, the NiSe_2 electrode is assembled with an active carbon(AC) electrode to form an asymmetric supercapacitor with an extended potential window of 1.6 V. The asymmetric supercapacitor possesses an excellent energy density 32.7 Wh kg~(-1) with a power density 800 W kg~(-1) at the current density of 1 A g~(-1). The nanosheet array on carbon fiber cloth with high flexibility, specific capacitance and rate capacitance render the NiSe_2 to be regarded as the promising material for the high performance superconductor.     

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.     

Facile Self-templating Melting Route Preparation of Biomass-derived Hierarchical Porous Carbon for Advanced Supercapacitors

Biomass-derived porous carbons show great potential as electrode materials for supercapacitors due to the environmental friendliness. However, most of the carbonaceous electrode materials suffer from low specific capaci-tance and rate capacity because of the poor porosity. Here, we reported a simple and effective approach to prepare micro/nano-hierarchical structured carbon materials derived from rice husk by NaOH-KOH molten salt co-activation. The as-prepared activated carbons exhibit high porosity and suitable pore size distributions for more electrolyte ion adsorption, which are all beneficial for achieving remarkable electrochemical performances, such as high specific capacitance(194.6 F/g), excellent rate capability(retention of 85.9%) and outstanding cycling stability. Thus, the above biomass-derived carbon materials with high porosity and micro/nano structures obtained by co-activation method offered a new insight into novel electrode material for the use in energy storage systems with high energy density and excellent rate performance.