Synthesis of mesoporous hollow carbon microcages by combining hard and soft template method for high performance supercapacitors

Carbon materials have been widely used in electrochemistry filed such as supercapacitors because of the good conductivity, abundant sources and low prices. Further improving the electrochemical performance of carbon materials still attracts the interest of researchers. In this work, nitrogen-doped mesoporous hollow carbon microcages (N-MHCC) are successfully prepared by combining hard and soft template method. This hierarchically porous structure (meso- & micro-pore) of N-MHCC provides a large number of active centers, sufficient space and reaction interface, promoting the rapid diffusion of electron and electrolyte ions transport. By comparing the electrochemical performance of nitrogen-doped hollow carbon microcages (N-HCC) and N-MHCC, it can be calculated that N-MHCC shows high specific capacitance of 210.66 F g^?1 at 0.5 A g^?1 while N-HCC only shows 132.6 F g^?1. The cycle retention rate of N-MHCC is as high as 96.92 % at 5 A g^?1 after 4000 cycles. Furthermore, the simple preparation method and attractive performance make N-MHCC a promising candidate for high performance supercapacitors.     

Improved output performance of hybrid composite films with nitrogen-doped reduced graphene oxide

In this research, graphene-based ceramic/polymer hybrid composite films for energy harvesting devices were prepared and analyzed. Nitrogen-doped reduced graphene oxide (N-rGO) conductive elements were embedded in a ceramic/polymer matrix as floating electrodes to form a micro-capacitor composite structure. The effects of nitrogen atom substitution on the rGO materials were investigated and their conducting properties improved. The employment of rGO- and N-rGO-based floating electrodes resulted in the formation of micro-capacitors and an increase in the potential energy of the composite films. The increase in the potential energy consequently increased the output energy of the energy harvesters. The highest voltage and energy density of the composite films were 8.5 V and 1.46 mJ/cm³, respectively, for the N-rGO based ceramic/polymer composite film.     

Ni/NiO multivalent system encapsulated in nitrogen-doped graphene realizing efficient activation for non-enzymatic glucose sensing

Nowadays, given the booming demand of blood sugar control from the soaring number of diabetes patients and the insufficient stability of costly enzyme-based glucose sensors in clinic, the development of enzyme-free sensors has been drawing tremendous attraction. Herein, we fabricated a unique structure of Ni/NiO hybrid nanoparticles with mixed-valence states encapsulated in and cross-linked by nitrogen-doped graphene via a facile Ni-MOF-annealing approach and developed its notable feature in efficiently non-enzymatic glucose sensing. The microstructure and valence states, proved vital to the electrochemical activity and sensing performance, were simultaneously regulated by the annealing temperature. The optimized sample obtained at 400 °C displays the superior activation behavior and best glucose sensing performance, offering a high sensitivity of 3.2518 mA mM^?1 cm^?2, a wide linear range (0.001–3.568 mM), a low detection limit (0.032 μM, S/N = 3) as well as excellent selectivity, good reproducibility, long-term stability, and satisfactory applicability in real sample. By further investigation of the electrochemical kinetics mechanism, the synergistic effect of multivalent system and well-organized microstructure was proved beneficial for charge transfer, activation of reaction sites, and elimination of electrode polarization as well, thus providing a promising strategy in designing non-enzymatic biosensor platform for glucose detection in actual diagnosis.     

Synthesis of ruthenium-embedded nitrogen-doped graphene for carbon dioxide hydrogenation

Two-dimensional (2D) layered materials have attracted great interest in the energy storage and catalysis field due to their graphene-like structure and excellent performance. Ruthenium-embedded nitrogen-doped graphene (Ru-NG) have been obtained by a novel method, using montmorillonite as hard template and Ru-phenanthroline chelate as precursor. After calcination in N₂ atmosphere at 800℃, Ru-NG were obtained and further characterized by X-ray diffraction (XRD), transmission electron microscopy (TEM), Raman spectroscopy, X-ray photoelectron spectroscopy (XPS) and nitrogen sorption. Ru-NG have 2D layered structure just like the montmorillonite template, and C, N, O and Ru are homogeneously distributed on them. The average sizes of Ru nanoparticles do not change much with the increasing of Ru content, and they keep at about 1.2 to 1.4 nm. The XPS results indicate that phenanthroline has been successfully transformed to nitrogen-doped carbon during pyrolysis, and the peaks at 398.5, 400.1 and 401.5 eV suggest the presence of pyridine-like, pyrrole-like and quaternary nitrogen atoms, respectively. Compared with the Ru catalyst supported on activated carbon prepared by the traditional impregnation-reduction method, Ru-NG exhibits excellent catalytic activity in the reaction of hydrogenation of carbon dioxide to formic acid.     

负载钌的氮掺杂石墨烯催化剂的制备及应用

利用人工合成的蒙脱石做硬模板,以插层的邻菲罗啉-钌络合物为前体,在惰性气氛下热解后用氢氟酸和盐酸刻蚀除去蒙脱石模板制备出负载钌纳米粒子的氮掺杂石墨烯催化剂(Ru-NG)。Ru-NG具有与模板蒙脱石类似的层状石墨烯结构,C、N、O及Ru元素在其上分布均匀。Ru-NG中钌的含量随钌前体的加入量的增加而增加,但受蒙脱石片层的物理限域作用及与含氮物种的配位作用,钌纳米粒子的粒径却无显著变化,且粒径均一,平均粒径在1.2～1.4 nm范围内。与传统浸渍-还原法制备的活性炭负载的Ru催化剂相比,Ru-NG在二氧化碳加氢生成甲酸反应中表现出优异的催化活性。     

Preparation of scale-like nickel cobaltite nanosheets assembled on nitrogen-doped reduced graphene oxide for high-performance supercapacitors

Ultrathin scale-like nickel cobaltite (NiCo₂O₄) nanosheets supported on nitrogen-doped reduced graphene oxide (N-rGO) are successfully synthesized through a facile co-precipitation of Ni²⁺ and Co²⁺ in the presence of sodium citrate and hexamethylenetetramine and subsequent calcination treatment. The composition and morphology of NiCo₂O₄ nanosheets@nitrogen-doped reduced graphene oxide (denoted as NiCo₂O₄ NSs@N-rGO) were characterized by Scanning electron microscope, Transmission electron microscope, X-ray diffraction, Raman spectra, X-ray photoelectron spectroscopy, Brunauer–Emmett–Teller and thermogravimetric analysis. The thickness of NiCo₂O₄ nanosheets anchored on the reduced graphene oxide is around 4 nm. The capacitance of NiCo₂O₄ NSs@N-rGO is evaluated by cyclic voltammogram and galvanostatic charge/discharge with the result that the NiCo₂O₄ NSs@N-rGO could deliver a specific capacitance of 1540 F g⁻¹ after 1000 cycles at 10 A g⁻¹.     

Synthesis of reduced graphene oxide/tungsten trioxide nanocomposite electrode for high electrochemical performance

A facile and well-controllable reduced graphene oxide/tungsten trioxide (rGO/WO₃) nanocomposite electrode was successfully synthesized via an electrostatic assembly route at 350 rpm for 24 h. In this study, hexagonal-phase WO₃ (h-WO₃) nanofiber was well distributed on rGO sheets by applying optimal processing parameters. The as-synthesized rGO/WO₃ nanocomposite electrode was compared with pure h-WO₃ electrode. A maximum specific capacitance of 85.7 F g⁻¹ at a current density of 0.7 A g⁻¹ was obtained for the rGO/WO₃ nanocomposite electrode, which showed better electrochemical performance than the WO₃ electrode. The incorporation of WO₃ into rGO could prevent the restacking of rGO and provide favourable surface adsorption sites for intercalation/de-intercalation reactions. The impedance studies demonstrated that the rGO/WO₃ nanocomposite electrode exhibited lower resistance because of the superior conductivity of rGO that improved ion diffusion into the electrode. To evaluate the contribution of WO₃ to the rGO/WO₃ nanocomposite, the influence of mass loading of WO₃ on the capacitance was investigated.     

Electrochemical performance of in situ LiFePO4 modified by N-doped graphene for Li-ion batteries

LiFePO₄ modified by N-doped graphene (NG) with a three-dimensional conductive network structure was synthesized via a one-step in situ hydrothermal method. The effects of N amount of NG on the phase structure, morphology, and electrochemical properties of LiFePO₄ are investigated in this study. X-ray diffraction (XRD) results show that doping suitable N amounts in NG do not alter the crystal structure of LiFePO_4, and scanning electron microscopy (SEM) images show that NG can slightly reduce the particle size of LiFePO₄. The high-resolution transmission electron microscopy (HRTEM) results show that the LiFePO₄ particles are well covered and connected by NG. The electrochemical performance confirms that LiFePO₄ modified by 20% N-doped graphene (named LFP/NG-4) displays a perfect specific capacity of 166.6 mAh·g^?1 at a rate of 0.2C and can reach 125 mAh·g^?1 at a rate of 5 C. Electrochemical impedance spectroscopy (EIS) results illustrate that the charge transfer resistance value of the LFP/NG-4 composite is only 58.6 Ω, which is very low compared with LiFePO₄. Cyclic voltammetry (CV) tests indicate that the addition of 20% N-doped graphene can effectively reduce electrode polarization and improve reversibility. The LFP/NG-4 composite with a three-dimensional conductive network structure can be regarded as a promising cathode material for Li-ion batteries.     

石墨烯气凝胶的制备及其对水中油分的吸附特性

以改性Hummers法制备出的氧化石墨（GO）为原料,乙二胺（EDA）为交联剂,通过液相化学交联法制备出以石墨烯为主体的多孔网状气凝胶（EGA）。利用电子扫描电镜（SEM）、电子透射电镜（TEM）及选区电子衍射（SAED）对其进行表征。以水中柴油为研究对象,考察所制EGA样品对水中柴油的吸附脱除效果。结果表明,石墨烯气凝胶对柴油的吸附量在前5 min上升迅速,在30 min左右达到吸附平衡。吸附过程遵循准二级动力学模型,且吸附速率随温度的升高而增加,体系的表观活化能E_a=23.94 kJ·mol^-1。颗粒内扩散模型拟合结果表明,EGA对水中柴油的吸附分为表面孔道吸附、气凝胶内部孔道扩散以及石墨烯片层间小孔道扩散。石墨烯气凝胶对柴油的吸附等温线与Freundlich模型较为吻合。     

Nano graphene porous/conductive polymer as a composite material for energy storage in supercapacitors

This research studies the improving effects of graphene porous (GP) on the supercapacitive performance of a polyaniline/graphene porous (PANI/GP) nanocomposite. GP nanosheets were synthesized via chemical vapor deposition, and PANI/GP was electrochemically composited through successive cyclic voltammetry. The samples were characterized by fast Fourier transform infrared (FTIR), x-ray diffraction (XRD), and scanning electron microscopy (SEM), and energy-dispersive x-ray spectrometry (EDS) techniques. Porous GP nanosheets were uniformly dispersed in the composite structure. Furthermore, the electrochemical performances of the synthesized samples were compared using galvanostatic charge/discharge, electrochemical impedance spectroscopy (EIS), and cyclic voltammetry (CV). Incorporating GP into the PANI significantly increased specific capacitance from 276 (in PANI) to 577 F/g (in PANI/GP). The electrochemical stability of electrodes was compared during 1000 successive charge/discharge cycles. After 1000 cycles, PANI/GP kept 90% of its initial capacitance, and only 25% of the charge storage capacitance of bare PANI remained.     

Hierarchical framework of CoZnS as a high-performance electrode material for supercapacitors

Efficient renewable energies are needed to meet the energy demands of modernized civilization. Therefore, this study evaluated composite Co_1-xZn_xS (0.04 ≤ x ≤ 0.34) (CZS-1 to CZS-6) thin film electrodes produced using a chemical growth approach as effective energy storage devices. Systematic integration of Zn²⁺ in the CoS host formed the polycrystalline Co_0.24SZn_0.76 (cubic) phase. The electrochemical measurements revealed a high diffusion rate and low series resistance, resulting in an excellent specific capacitance (C_s) of 1288 F g^?1 at a current density of 2 mA cm^?2 with better rate performance. In addition, the optimal electrode (CZT-5) showed a better power density of 8.86 kW kg^?1 and an energy density of 44.4 Wh kg^?1 with excellent capacitive retention (85% after 5000 cycles). The enhanced performance could stem from the spongy rose flower-like nanostructure with a covered network of polygonic petals. Consequently, the replacement of Co²⁺ with Zn²⁺ also contributed by exchanging the oxidation states of targeted atoms, including Co²⁺, Co³⁺, Zn²⁺, and S^2?. Moreover, surface topographical insight states that crystalline growth of the CZS samples with hillocks and valleys and CZS-5 sample exhibited maximum total roughness.     

Synthesis of carbon-coated graphene electrodes and their electrochemical performance

In this work, C-graphene composed of core graphene and carbon shells was prepared to obtain a new type of carbon electrode materials. Carbon shells containing nitrogen groups were prepared by coating polyaniline (PANI) onto graphene by in situ polymerization and subsequent carbonization at 850 °C. After carbonization, the C-graphene contained 6.5% nitrogen and showed a 2D plate structure and crystallinity like that of pristine graphene. In addition, the C-graphene exhibited electrochemical performance superior to that of pristine graphene, and the highest specific capacitance (170 F/g) of the C-graphene was obtained at a scan rate of 0.1 A/g, as compared to 138 F/g for pristine graphene. This superior performance was attributed to the synergistic effect of porous carbon layer and the graphene and the pseudocapacitive effect by the nitrogen groups formed on the carbon electrode after carbonization.     

Synthesis of Mn3O4/N-doped graphene hybrid and its improved electrochemical performance for lithium-ion batteries

Mn₃O₄/N-doped graphene (Mn₃O₄/NG) hybrids were synthesized by a simple one-pot hydrothermal process. The scanning electron microscopy (SEM), transition electron microscopy (TEM), X-ray powder diffraction (XRD), Thermogravimetric analysis (TG), Raman Spectroscopy and X-ray photoelectron spectroscopy (XPS) were used to characterize the microstructure, crystallinity and compositions. It is demonstrated that Mn₃O₄ nanoparticles are high-dispersely anchored onto the individual graphene nanosheets, and also found that, in contrast with pure Mn₃O₄ obtained without graphene added, the introduction of graphene effectively restricts the growth of Mn₃O₄ nanoparticles. Simultaneously, the anchored well-dispersed Mn₃O₄ nanoparticles also play a role as spacers in preventing the restacking of graphene sheets and producing abundant nanoscale porous channels. Hence, it is well anticipated that the accessibility and reactivity of electrolyte molecules with Mn₃O₄/NG electrode are highly improved during the electrochemical process. As the anode material for lithium ion batteries, the Mn₃O₄/NG hybrid electrode displays an outstanding reversible capacity of 1208.4 mAh g⁻¹ after 150 cycles at a current density of 88 mA g⁻¹, even still retained 284 mAh g⁻¹ at a high current density of 4400 mA g⁻¹ after 10 cycles, indicating the superior capacity retention, which is better than those of bare Mn₃O₄, and most other Mn₃O₄/C hybrids in reported literatures. Finally, the superior performance can be ascribed to the uniformly distribution of ultrafine Mn₃O₄ nanoparticles, successful nitrogen doping of graphene and favorable structures of the composites.     

有机添加剂对超级电容器中水系电解液理化性能的影响

以6 mol/L KOH水溶液为电解液,高比表面积的活性炭为活性物质,研究了有机添加剂对体系润湿性、电导率、工作电压窗口及阻抗的影响,测试了超级电容器的电化学性能。结果表明,适量添加有机添加剂可明显抑制体系的极化现象,提高超级电容器的工作电压窗口。添加10vol%异丙醇时,电极材料和电解液间的润湿性大幅提高,比电容从79.3 F/g提高至113.2 F/g。添加20vol%异丙醇时,超级电容器的能量密度达19.4 Wh/kg,体系的电荷转移电阻明显降低,在10 A/g电流密度下的比电容比0.5 A/g时下降13.9%,而不加添加剂时下降30.3%。添加30vol%异丙醇时,电解液电导率迅速下降,比电容降低,电导率是影响比电容的关键因素。     

Facile synthesis and electrochemical performances of hollow graphene spheres as anode material for lithium-ion batteries

The hollow graphene oxide spheres have been successfully fabricated from graphene oxide nanosheets utilizing a water-in-oil emulsion technique, which were prepared from natural flake graphite by oxidation and ultrasonic treatment. The hollow graphene oxide spheres were reduced to hollow graphene spheres at 500°C for 3 h under an atmosphere of Ar(95%)/H₂(5%). The first reversible specific capacity of the hollow graphene spheres was as high as 903 mAh g^-1 at a current density of 50 mAh g^-1. Even at a high current density of 500 mAh g^-1, the reversible specific capacity remained at 502 mAh g^-1. After 60 cycles, the reversible capacity was still kept at 652 mAh g^-1 at the current density of 50 mAh g^-1. These results indicate that the prepared hollow graphene spheres possess excellent electrochemical performances for lithium storage. The high rate performance of hollow graphene spheres thanks to the hollow structure, thin and porous shells consisting of graphene sheets.

PACS

81.05.ue; 61.48.Gh; 72.80.Vp     

Preparation and characterization of cotton fibers coated with AA-IA hydrogel containing silver/graphene or graphene oxide nanoparticles

This study presents the fabrication and characterization of cotton textile fibers coated with hydrogels containing silver and Graphene or Graphene Oxide nanoparticles using 1-hexyl-3-methyl-imidazolium (HMIMPF6) ionic liquid (IL) as carbon filler dispersant. Acrylic acid/Itaconic acid (AA-IA) hydrogels are synthesized by polymerizing an acrylic acid-itaconic acid aqueous (80/20 v/v) solution and mixed with 2-2-Azobis (2-methylpropionamide) diclorohydrate, and N,N´-methylenbis (acrylamide). Then silver nanoparticles are generated throughout the hydrogel networks using in situ method by incorporating the silver ions and subsequent reduction with sodium borohydride. Then a cotton textile fiber substrate was coated with this hydrogel. Finally, graphene or graphene oxide was added to the textile substrate already impregnated with hydrogel and silver nanoparticles. In order to favor the dispersion of the carbon nano-structures in the system, an IL was used. The influence of these nanocomposite hydrogels on the properties of textile fiber were investigated by infrared spectroscopy (ATR), scanning electron microscopy (SEM), inductively coupled plasma mass spectroscopy (ICP) and antibacterial tests against Staphylococcus aureus (Gram positive) and Escherichia coli (Gram negative). The effect of each and combined fillers dispersion on antimicrobial properties were determined. Cotton fibers coated with hydrogel containing silver nanoparticles and graphene showed better results when the ionic liquid was used. Graphene showed greater antimicrobial efficiency than graphene oxide. It was proved that the textiles coated with hydrogels containing these fillers had an excellent antibacterial ability and are a good option to be used for medical applications such as wounds and burns dressing.     

Solvothermal synthesis of porous MnCo2O4.5 spindle-like microstructures as high-performance electrode materials for supercapacitors

This study presents the facile preparation of novel MnCo₂O_4.5 microspindles (MSs) for the first time through a rapid solvothermal method combined with subsequent calcination of the precursor at 450 °C for 4 h in air. The MnCo₂O_4.5 MSs have an average length of 4–5 µm and diameter of 2–4 µm, respectively, achieving a specific surface area as high as 83.3 m² g⁻¹. In addition, the size and morphology of the MnCo₂O_4.5 microstructures could be easily tuned by some parameters including reaction time, volume ratio of ethanol to water, and dosage of urea. The electrochemical performance was further evaluated in three-electrode system, detailed electrochemical characterizations revealed that such MnCo₂O_4.5 MSs exhibited both high specific capacitance of 343 F g⁻¹ at a current density of 0.5 A g⁻¹ and excellent cycling performance of 81.3% capacitance retention after 5000 cycles at a current density of 4 A g⁻¹ in 2 M of KOH electrolyte, which made it a potential electrode material for an advanced supercapacitor. Furthermore, the present synthetic method is simple and can be extended to the synthesis of other electrode materials based on transition metal oxides.     

Facile synthesis of polypyrrole nanospheres and their carbonized products for potential application in high-performance supercapacitors

A facile method to prepare uniform polypyrrole (PPy) nanospheres is developed by using 3-chloroperbenzoic acid as oxidant, structure-induced reagent and dopant for polymerization of pyrrole without introducing extra acid, template and surfactant. The as-synthesized PPy nanospheres with an average diameter of 100–200 nm and conductivity about 10⁻² S cm⁻¹ are characterized by SEM, FTIR, UV–vis spectroscopy, XRD and elemental analysis in an effort to determine the identity of the nanospheres and the mechanism relevant to their formation and stabilization. Influences of experimental conditions on the morphology of the PPy nanospheres have been investigated. Via the high temperature pyrolyzation at 900 °C, the nitrogen-doped carbon nanospheres have been obtained from the PPy nanospheres precursors, which have a high conductivity of 10–100 S cm⁻¹, showing a good potential as the electrode materials for high-performance supercapacitors due to their excellent electrochemical performance.     

石墨烯纳米片/CoS2复合材料的制备及其在超级电容器中的应用

采用一步水热法制备石墨烯纳米片（GNS）/CoS₂复合材料,利用XRD和SEM对所制备复合材料的微观结构进行表征,采用循环伏安法和交流阻抗法对复合材料的电化学性能进行研究。研究结果表明,在水热过程中,氧化石墨（GO）逐渐被还原成石墨烯纳米片（GNS）,能够为CoS₂晶核的形成提供更多的接触点,有利于CoS₂颗粒均匀地生长在GNS表面。这种结构的复合材料既能够显著增加CoS₂和电解液之间的有效接触面积,提高CoS₂的电化学利用率,同时又能够改善材料的导电性,有利于提高材料的比电容。     

Copper substituted nickel ferrite nanoparticles anchored onto the graphene sheets as electrode materials for supercapacitors fabrication

Nickel ferrites with high theoretical capacitance value as compared to the other metal oxides have been applied as electrode material for energy storage devices i.e. batteries and supercapacitors. High tendency towards aggregation and less specific surface area make the metal oxides poor candidate for electrochemical applications. Therefore, the improvements in the electrochemical properties of nickel ferrites (NiFe₂O₄) are required. Here, we report the synthesis of graphene nano-sheets decorated with spherical copper substituted nickel ferrite nanoparticles for supercapacitors electrode fabrication. The copper substituted and unsubstituted NiFe₂O₄ nanoparticles were prepared via wet chemical co-precipitation route. Reduced graphene oxide (rGO) was prepared via well-known Hummer's method. After structural characterization of both ferrite (Ni_1-xCu_xFe₂O₄) nanoparticles and rGO, the ferrite particles were decorated onto the graphene sheets to obtain Ni_1-xCu_xFe₂O₄@rGO nanocomposites. The confirmation of preparation of these nanocomposites was confirmed by scanning electron microscopy (SEM). The electrochemical measurements of nanoparticles and their nanocomposites (Ni_0.9Cu_0.1Fe₂O₄@rGO) confirmed that the nanocomposites due to highly conductive nature and relatively high surface area showed better capacitive behavior as compared to bare nanoparticles. This enhanced electrochemical energy storage properties of nanocomposites were attributed to the graphene and also supported by electrical (I-V) measurements. The cyclic stability experiments results showed ~65% capacitance retention after 1000 cycles. However this retention was enhanced from 65% to 75% for the copper substituted nanoparticles (Ni_0.9Cu_0.1Fe₂O₄) and 65–85% for graphene based composites. All this data suggest that these nanoparticles and their composites can be utilized for supercapacitors electrodes fabrication.