Interactive effects of pore size control and carbonization temperatures on supercapacitive behaviors of porous carbon/carbon nanotube composites

Porous carbon-based electrodes were prepared by carbonization with poly(vinylidene fluoride) (PVDF)/carbon nanotube (CNT) composites to further increase the specific capacitance for supercapacitors. The specific capacitance, pore size distribution, and surface area of the PVDF/CNT composites were measured, and the effect of the carbonization temperatures was examined. The electrochemical properties were examined by cyclic voltammetry, impedance spectroscopy, and galvanostatic charge-discharge performance using a two-electrode system in TEABF(4) (tetraethylammonium tetrafluoroborate)/acetonitrile as a non-aqueous electrolyte. The highest specific capacitance of ～101 Fg(-1) was obtained for the samples carbonized at 600 °C. The pore size of the samples could be controlled to below 7 nm through the carbonization process. This suggests that micropores make a significant contribution to the specific capacitance due to improved charge transfer between the pores of the electrode materials and the electrolyte.     

Superior supercapacitive performance in porous nanocarbons

Porous nanocarbons with average particle size 20–40 nm were developed using biowaste oil palm leaves as a precursor.Simple pyrolysis was carried out at 700 °C under nitrogen atmosphere.Obtained porous nanocarbons showed excellent porous nature along with spherical shape.Symmetric supercapacitor fabricated from porous nanocarbons showed superior supercapacitance performance where high specific capacitance of 368 F/g at 0.06 A/g in 5 M KOH were reported.It also exhibited high stability(96% over 1700cycles) and energy density of 13 Wh/kg.Low resistance values were obtained by fitting the impedance spectra,thus indicating the availability of these materials as supercapacitors electrode.The presented method is cost effective and also in line with waste to wealth approach.     

Mechanistic and kinetic studies of crystallization of birnessite

Kinetic and mechanistic features have been studied for the crystallization of birnessite in aqueous systems via different synthesis methods: the oxidation of Mn2+, reduction of MnO4-, and redox reaction between Mn2+ and MnO4-. For oxidation methods, a topotactical conversion from Mn(OH)2 to birnessite via feitknechtite (beta-MnOOH) is observed. In reduction methods, birnessite evolves from the initially produced amorphous manganese oxide (AMO gel). For redox methods, both mechanisms exist, with the latter prevailing. A liquid mechanism is proposed to describe the reduction and redox synthesis, which comprises three stages: an induction period, a fast crystallization period, and a steady-state period. The redox method is accompanied by the formation and phase transformation of feitknechtite to birnessite. A method combining IR and XRD quantitation is proposed to detect nuclei in the induction period. Crystallization rates and apparent energies of activation of crystallization for reduction and redox methods are determined.     

硼、氮共掺杂多孔碳的制备及其超电容性能

分别以含氮菲咯啉、四硼酸钾和醋酸锌为碳源、活化剂和模板,制备了B、N共掺杂多孔碳(BN-PC),并探究模板质量对BN-PC结构和储电性能的影响。当醋酸锌质量为5g时,所得BN-PC₅中B、N杂原子含量分别为 20.21%、18.29%。电化学测试结果表明,以6 mol·L^-1 KOH为电解液,BN-PC₅电极展现出高的比电容(在0.05 A·g^-1电流密度下为255 F·g^-1)、优异的倍率性能(在20A·g^-1电流密度下为188F·g^-1)和卓越的循环稳定性(在5 A·g^-1的电流密度下循环10 000次比电容保持率为97%)。以3 mol·L^-1 ZnSO₄为电解液,在平均功率密度为56W·kg^-1时,BN-PC₅电容器的能量密度可达27Wh·kg^-1。     

硼、氮共掺杂多孔碳的制备及其超电容性能

分别以含氮菲咯啉、四硼酸钾和醋酸锌为碳源、活化剂和模板,制备了B、N共掺杂多孔碳(BN-PC),并探究模板质量对BN-PC结构和储电性能的影响。当醋酸锌质量为5 g时,所得BN-PC₅中B、N杂原子含量分别为20.21%、18.29%。电化学测试结果表明,以6 mol·L^-1KOH为电解液,BN-PC₅电极展现出高的比电容(在0.05 A·g^-1电流密度下为255 F·g^-1)、优异的倍率性能(在20 A·g^-1电流密度下为188 F·g^-1)和卓越的循环稳定性(在5 A·g^-1的电流密度下循环10 000次比电容保持率为97%)。以3mol·L^-1ZnSO₄为电解液,在平均功率密度为56 W·kg^-1时,BN-PC₅电容器的能量密度可达27 Wh·kg^-1。     

Electrochemical supercapacitive performance of potentiostatically cathodic electrodeposited nanostructured MnO2 films

Journal of Solid State Electrochemistry - Nanostructured MnO2 films were prepared via cathodic electrodeposition under potentiostatic condition. X-ray diffraction (XRD) analyses reveal that the...     

Controlled synthesis of mesoporous carbon nanosheets and their enhanced supercapacitive performance

Mesoporous carbon nanosheets (MCNs) were synthesized using porous magnesium oxide (MgO) layer as the template precursor and resol as the carbon source. The morphology of the mesoporous carbon particles can be easily controlled by altering the mass ratio of MgO to resol. The structural characterization demonstrates that the interlaced MCNs can be formed when MgO/resol is 1:1 and they possess the carbon nanolayer with a thickness of about 5 nm and a width of about 200 nm. The quantities of mesopores and micropores endow the MCNs with a large surface area of 1,180 m²?g^?1 and a high pore volume of 1.56 cm³?g^?1. The supercapacitive performance of carbon products synthesized with various MgO/resol ratios was evaluated using cyclic voltammetry and galvanostatic charge–discharge techniques. The results show that the interlaced MCNs exhibit the highest specific capacitance of 241 F?g^?1, the best rate capability and cycling stability, which are attributed to the fast electrolyte ion transport or diffusion throughout the electrode matrix and effective utilization of the electrical double-layer capacitance of carbon layer.     

The introduction of cobalt element into nickel-organic framework for enhanced supercapacitive performance

Metal-organic frameworks (MOFs) as promising electrodes for supercapacitors are attracting increasing research interest. Herein, we report an effective strategy to improve the electrochemical performance of Ni-MOF for supercapacitor by introducing a secondary Co ion. The Co substitution of Ni in Ni-MOF can improve the intrinsic reactivity and stability. As a result, the bimetallic Co/Ni-MOF-1:15 with an optimal Co/Ni ratio delivers high specific capacitance (359 F/g at 0.5 A/g), good rate performance (81.5% retention at 5 A/g) and cycling stability (81% retention after 5000 cycles). These results demonstrate that the bimetallic synergistic strategy is an effective way to improve the pseudocapacitive performance of MOFs.     

Electrochemical supercapacitive properties of polypyrrole thin films: influence of the electropolymerization methods

A detailed study of the effects of different electropolymerization methods on the supercapacitive properties of polypyrrole (PPy) thin films deposited on carbon cloth is reported. Deposition mechanisms of PPy thin films through cyclic voltammetry (CV), potentiostatic (PS), and galvanostatic (GS) modes have been analyzed. The resulting PPy thin films have been characterized by X-ray photoelectron spectroscopy (XPS), SEM, and TEM. The electrochemical properties of PPy thin films were investigated by cyclic voltammetry and galvanostatic charge/discharge. The results showed that the different electrodeposition modes of synthesis significantly affect the supercapacitive properties of PPy thin films. Among different modes of electrodeposition, PPy synthesized by a potentiostatic mode exhibits maximum specific capacitance of 166 F/g with specific energy of 13 Wh/kg; this is attributed to equivalent proportions of the oxidized and neutral states of PPy. Thus, these results provide a useful orientation for the use of optimized electrodeposition modes for the growth of PPy thin films to be applied as electrode material in supercapacitors.     

Enhanced effects of nano-scale topography on the bioactivity and osteoblast behaviors of micron rough ZrO2 coatings

Implant surface topography is one of the most important factors affecting the rate and extent of osseointegration. Randomly micron-roughened surfaces have been documented to support osteoblast adhesion, differentiation, and mineralized phenotype, and thus favoring bone fixation of implants to host tissues. However, few studies have been done yet to investigate whether their effects on osteoblast behaviors can be enhanced by incorporation of nano-scale topographic cues. To validate this hypothesis, zirconia coatings with micron roughness (about 6.6 μm) superimposed by nano-sized grains (<50 nm) were fabricated by plasma spraying. To validate the impact of nano-sized grains, post-treatments of surface polishing (SP) and heat treatment (HT) were performed on the as-sprayed (AS) coatings to change the surface topographies but keep the chemical and phase composition similar. Results of in vitro bioactivity test showed that apatite was formed only on coating surfaces with nano-sized grains (AS coatings), indicating the significance of nano-topographic cues on the in vitro bioactivity. Enhanced osteoblast adhesion and higher cell proliferation rate were observed on coatings with both micron-roughness and nano-sized grains (AS-coatings), compared to coatings with smooth surfaces (SP-coatings) and coatings with only micron-scale roughness (heat-treated coatings), indicating the significant effects of nano-size grains on osteoblast responses. As the micron rough surfaces have been well-documented to enhance bone fixation, results of this work suggest that a combination of surface modifications at both micron and nano-scale is required for enhanced osseointegration of orthopedic implants.     

Design of high-performance core-shell hollow carbon nanofiber@nickel-cobalt double hydroxide composites for supercapacitive energy storage

The supercapacitive performances of supercapacitor mainly depend on the physical nanostructure and micro-morphology of electrode materials. Here, we demonstrated the design, synthesis and electrochemical performances of core-shell hollow carbon nanofiber@nickel-cobalt-layered double hydroxide (HCNF@ Ni_0.67Co_0.33-LDH) nanocomposites with an optimized Ni/Co molar ratio of 2:1. The HCNF was used as superiorly conductive core to sustain the nanoporous silky Ni_0.67Co_0.33-LDH shell, which can efficiently provide fast transport pathways for electrons and electrolyte ions. The outstanding specific capacitance of 2486 F g^?1 at 1 A g^?1 based on galvanostatic charge-discharge curves were acquired for the highly electroactive HCNF@Ni_0.67Co_0.33-LDH. Furthermore, the HCNF@Ni_0.67Co_0.33-LDH electrode delivered a distinguished rate capability with a specific capacitance of 1890 F g^?1 even at 15 A g^?1. Notably, an asymmetric supercapacitor with HCNF@Ni_0.67Co_0.33-LDH as cathode and HCNF as anode was devised, which presented a prominent specific capacitance of 228 F g^?1, good energy density of 62.1 Wh kg^?1, and impressive cycling stability (90.6% capacitance retention after 10,000 cycles).     

Sorption of cobalt(II) on soil: effects of birnessite and humic acid

To study the sorption behavior of Co(II) on soil and soil components such as birnessite, humic acid (HA) and their mixture, a series of experiment were conducted using the batch equilibrium technique on parameters such as equilibrium time, ionic strength, solution pH, and temperature. The soil samples collected from location near radioactive waste repository in Korea were used and birnessite was synthesized using a method by McKenzie for experiment. The experimental results indicate that Co sorption on soil, birnessite and soil with birnessite are strongly affected by the pH of solution. Typical for metal sorption to soils, the fraction of Co adsorbed increased as a function of pH at the experimental conditions. For sorption isotherm, the Freundlich equation provides a good fit for sorption on soil and soil with birnessite. Adsorption of HA on birnessite decreased with increase of pH, with a sharp decrease at pH 5?C6. From Co sorption experiment in a ternary system of Co, birnessite, and HA, the presence of HA enhanced Co adsorption at pH below 6.5 and reduced the Co sorption at the intermediate and high pH.     

Simple synthesis of novel phosphate electrode materials with unique microstructure and enhanced supercapacitive properties

Flower-like Ni₃P₂O₈ and flower-like Fe₃P₂O₈·8H₂O have been successfully synthesized by a simple chemical precipitation method.X-ray diffraction（XRD） patterns reveal an amorphous phase formation of nickel phosphate（Ni₃P₂O₈） and pure monoclinic phase of Fe₃P₂O₈·8H₂O.The novel flower-like Ni₃P₂O₈ and flower-like Fe₃P₂O₈·8H₂O when used for supercapacitor electrode materials exhibit a high specific capacitance（C m） of 1464 F/g and 200 F/g at a current density of 0.5 A/g,respectively.Eventually,an asymmetric supercapacitor is fabricated using Ni₃P₂O₈ as positive electrode and Fe₃P₂O₈·8H₂O as negative electrode.A high specific capacitance of 94 F/g is achieved in the high-voltage region of 0 ～1.6 V,and a large energy density of 32.6 Wh/kg is delivered at power density of 420 W/kg.The findings demonstrate the important and great potential of developing metal phosphate based materials for supercapacitors.     

Fabrication and supercapacitive performance of long anodic TiO2 nanotube arrays using constant current anodization

A galvanostatic anodization is used to prepare long TiO₂ nanotube arrays (TNTAs). TNTAs of over 100 μm in length, with similar nanotube size and structural regularity to the classic TNTAs made from potentiostatic mode, are achieved at 10 mA cm^− 2. After a post-anodization in a H₃PO₄-based electrolyte, the TNTAs with long nanotubes exhibit good adhesion to Ti substrate. The as-prepared long TNTAs yield a larger areal capacitance of 128.4 mF cm^− 2. Further, the long TNTAs possess a higher surface area, making them suitable as support templates for other active materials.     

Improved supercapacitive performance of low pore size and highly stable nanostructured NiCo2O4 electrodes

Journal of Solid State Electrochemistry - The nanostructured nickel cobaltite has been synthesized by a cost-effective facile hydrothermal method and demonstrated excellent electrochemical...     

Enhanced crystallization behaviors of poly(ethylene terephthalate) via adding expanded graphite and poly(ethylene glycol)

A compound additive system consisting of expanded graphite (EG) and poly(ethylene glycol) (PEG) was designed to enhance the crystallization of poly(ethylene terephthalate) (PET). In this additive system, EG acted as a heterogeneous nucleating agent to reduce energy barrier for nucleation, while PEG played as plasticizer to improve mobility of PET chains. Simultaneously adding EG and PEG resulted in faster crystallization kinetics than the cases of solely adding EG or PEG in both of non-isothermal and isothermal crystallization processes, indicating a synergistic effect of EG and PEG on enhancing PET crystallization. However, for non-isothermal crystallization process, in which crystallization occurred from a cooling melt, EG played a dominant role. As to isothermal crystallization process where crystallization took place in a super-cooling state, PEG seemed to be more important. Moreover, the chain conformation change among the semi-crystalline PET specimens was ascertained by Fourier transform infrared spectroscopy.     

Fabrication of sulfonated mesoporous carbon by evaporation induced self-assembly/carbonization approach and its supercapacitive properties

Synthesis of functionalized mesoporous carbon by an easy-accessed method is of great importance towards its practical applications.Herein,an evaporation induced self-assembly/carbonization(EISAC) method was developed and applied to the synthesis of sulfonic acid group functionalized mesoporous carbon(SMC).The final mesoporous carbon obtained by EISAC method possesses wormlike mesoporous structure,uniform pore size(3.6 nm),large surface area of 735 m²/g,graphitic pore walls and rich sulfonic acid group.Moreover,the resultant mesoporous carbon achieves a superior electrochemical capacitive performances(216 F/g)to phenolic resin derived mesoporous carbon(OMC,152 F/g)and commercial activated carbon(AC,119 F/g).     

低温热处理制备石墨烯-氧化钴及其超级电容性能

采用简单的水热法制备出功能化石墨烯与CoOOH的复合物,再通过低温热处理得到功能化石墨烯-Co3O4复合材料;采用扫描电子显微镜分析了样品的形貌;测定了其电化学性能和氮气吸脱附行为.结果表明,Co3O4粒子很好地负载在石墨烯片层之间和表面;形成的复合物具有纳米孔道结构,这些纳米孔道结构有利于电解液离子的传输;而石墨烯良好的导电性有利于电子传递和提高Co3O4粒子的电容贡献值.与此同时,复合物在充放电电流密度为1A/g时的电容达320F/g,表现出优异的超电容性能.     

Effect of carboxylic acid groups on the supercapacitive performance of functional carbon frameworks derived from bacterial cellulose

Three-dimensional(3D) carbonaceous materials derived from bacterial cellulose(BC) has been introduced as electrode for supercapacitors in recent. Here, we report a simple strategy for the synthesis of functional carbon frameworks through 2,2,6,6-tetramethylpilperidine 1-oxyl radical(TEMPO)-mediated oxidation of bacterial cellulose(BC) followed by carbonization. TEMPO-mediated oxidation can efficiently convert the hydroxyls on the surface of BC to carboxylate groups to improve electrochemical activity. Because of its high porosity, good hydrophilicity, rich oxygen groups, and continuous ion transport in-between sheet-like porous network, the TEMPO-oxidized BC delivers a much higher gravimetric capacitance(137.3 F/g) at low annealing temperature of 500℃ than that of pyrolysis BC(31 F/g) at the same annealing temperature. The pyrolysis modified BC obtained at 900℃ shows specific capacitance(160.2 F/g), large current stability and long-term stability(84.2% of its initial capacitance retention after 10,000 cycles).