首页 | 本学科首页   官方微博 | 高级检索  
相似文献
 共查询到20条相似文献,搜索用时 31 毫秒
1.
Jun Yan  Bo Shao  Weizhong Qian  Fei Wei 《Carbon》2010,48(2):487-784
A graphene nanosheet (GNS)/polyaniline (PANI) composite was synthesized using in situ polymerization. The morphology and microstructure of samples were examined by scanning electron microscopy (SEM), transition electron microscopy (TEM), X-ray diffraction (XRD) and Raman spectroscopy. Electrochemical properties were characterized by cyclic voltammetry (CV) and galvanostatic charge/discharge. GNS as a support material could provide more active sites for nucleation of PANI as well as excellent electron transfer path. The GNS was homogeneously coated on both surfaces with PANI nanoparticles (∼2 nm), and a high specific capacitance of 1046 F g−1 (based on GNS/PANI composite) was obtained at a scan rate of 1 mV s−1 compared to 115 F g−1 for pure PANI. In addition, the energy density of GNS/PANI composite could reach 39 W h kg−1 at a power density of 70 kW kg−1.  相似文献   

2.
Shifeng Yan  Yan Yang  Jia Ma 《Polymer》2007,48(6):1688-1694
A new surface modification method by grafting l-lactic acid oligomer onto the surface silanol groups of silica nanoparticles has been developed. The surface-grafting reaction is confirmed by IR and 29Si MAS NMR analyses. TEM and SEM results show that grafted SiO2 (g-SiO2) nanoparticles can be comparatively uniformly dispersed in chloroform or PLLA matrix, while the unmodified SiO2 nanoparticles tend to aggregate. The loading of g-SiO2 nanoparticles in poly(l-lactide) (PLLA) matrix greatly improves the toughness and tensile strength of this material. In contrast, the incorporation of un-grafted SiO2 nanoparticles into PLLA leads to the deterioration of its mechanical properties. DSC analysis shows that g-SiO2 nanoparticles can serve as a nucleating agent for the crystallization of PLLA in the composites. SEM characterization shows the tough characteristics and great interfacial combination strength for g-SiO2 (5 wt%)/PLLA nanocomposites.  相似文献   

3.
Nanowire-structured MnO2 active materials were prepared by a chemical precipitation method and their supercapacitive properties for use in the electrodes of supercapacitors were investigated by means of cyclic voltammetry in an aqueous gel electrolytes consisting of 1 M Na2SO4 and fumed silica (SiO2). The MnO2 electrode showed a maximum specific capacitance of 151 F g−1 after 1000 cycles at 100 mV s−1 when using the gel electrolyte containing 3 wt.% of SiO2, which is higher than 121 F g−1 obtained when using the 1 M Na2SO4 liquid electrolyte alone.  相似文献   

4.
The electrosynthesis of polyaniline on the bare aluminum and pre-treated aluminum surface achieved in aqueous H2PtCl6 solution saturated with NaF for few seconds is described. The effect of some factors such as pre-treatment time, aniline and sulfuric acid concentrations on the electropolymerization process was investigated and optimum conditions were obtained. The stability of polyaniline film on the pre-treated aluminum electrode (Al-Pt) was studied as function of the potential imposed on the electrode. For applied electrode potentials of 0.1-0.7 V, the first-order degradation rate constant, k, of polyaniline film varies between 1 × 10−6 and 2 × 10−5 s−1, and a relatively low slope (i.e. 2.1) was obtained for the plot of log k versus E. The coatings were characterized by scanning electron microscopy (SEM), and cyclic voltammetric behavior of the polyaniline-deposited Al electrode (Al/PANI) and polyaniline-deposited Al-Pt electrode (Al-Pt/PANI) in 0.1 H2SO4 solutions is described. The electrocatalytic activity of the Al-Pt/PANI electrode against para-benzoquinone/hydroquinone (Q/H2Q) and Fe(CN)63−/Fe(CN)64− redox systems was investigated and the obtained results are compared with those obtained on Al/PANI and bulk Pt electrodes.  相似文献   

5.
A polyaniline (PANI)/silica (SiO2) composite film was prepared by a simple in situ electrodeposition method, and its electrochromic (EC) properties were studied. When PANI was electrodeposited in the presence of SiO2 particles, the resulting PANI/SiO2 composite films possessed higher surface areas, larger redox charge capacities, and higher doping levels, thus enhanced optical contrasts. By incorporating SiO2 particles into the PANI film, the transmittance change at 700 nm from 10.7% to 16.4%, or an enhancement of ca. 50%, was achieved when operating between −0.5 V and 0 V. In addition, x-ray photoelectron spectroscopy (XPS) indicated that the formation of the highly oxidized PANI might have been retarded through the addition of SiO2 particles. Furthermore, the growth mechanism of the PANI/SiO2 composite film was proposed.  相似文献   

6.
A ternary composite of CNT/polypyrrole/hydrous MnO2 is prepared by in situ chemical method and its electrochemical performance is evaluated by using cyclic voltammetry (CV), impedance measurement and constant-current charge/discharge cycling techniques. For comparative purpose, binary composites such as CNT/hydrous MnO2 and polypyrrole/hydrous MnO2 are prepared and also investigated for their physical and electrochemical performances. The specific capacitance (SC) values of the ternary composite, CNT/hydrous MnO2 and polypyrrole/hydrous MnO2 binary composites estimated by CV technique in 1.0 M Na2SO4 electrolyte are 281, 150 and 35 F g−1 at 20 mV s−1 and 209, 75 and 7 F g−1 at 200 mV s−1, respectively. The electrochemical stability of ternary composite electrode is investigated by switching the electrode back and forth for 10,000 times between 0.1 and 0.9 V versus Ag/AgCl at 100 mV s−1. The electrode exhibits good cycling stability, retaining up to 88% of its initial charge at 10,000th cycle. A full cell assembled with the ternary composite electrodes shows a SC value of 149 F g−1 at a current loading of 1.0 mA cm−2 during initial cycling, which decreased drastically to a value of 35 F g−1 at 2000th cycle. Analytical techniques such as scanning electron microscopy (SEM), X-ray diffraction spectroscopy (XRD), Brunauer-Emmet-Teller (BET) surface area measurement and inductively coupled plasma-atomic emission spectrometry (ICP-AES) are also used to characterize the composite materials.  相似文献   

7.
To more accurately investigate the nucleation, crystallization and dispersion behaviors of silica particles in polymers, the composites of PET with monodisperse SiO2-PS core-shell structured particles were prepared with SiO2 size from 380 nm to 35 nm.For these SNPET samples, DSC results showed that the nucleation rate of silica particles increased as their size decreased, in which 35 nm SiO2 particles produced the most obvious nucleation effect. At 2.0 wt.% load of 35 nm silica, Avrami equation proved that the isothermal crystallization rate G of SNPET was ca. 30% higher than that of pure PET and the crystallization activation energy for SNPET was −218.7 kJ mol−1 lower than −196.1 kJ mol−1 for PET. While, the non-isothermal crystallization ΔE for SNPET was −199.8 kJ mol−1 lower than −185.5 for PET.On non-isothermal crystallization, Jeziorny equation presented the primary and secondary crystallization stages in PET and SNPET, in which nano SiO2 accelerated the crystallization rate. Their Ozawa number m was from 2.1 to 2.7, which was smaller than that of Avrami number n.The nucleation and dispersion behaviors of SiO2 particles were directly observed. POM results demonstrated that SNPET samples crystallized more quickly from melt and their crystallization rate increased as silica load increases but accelerated at 2-3 wt.%. The spherulites grew well in PET but their size was smaller in SNPET due to the silica barrier on their growth. SEM and TEM observed the homogeneous silica dispersion morphology and the vivid ordered patterns formed in SNPET. The monodisperse particles are highly expected to give more accurate and valuable references than multi-scale ones in obtaining novel advanced PET composites.  相似文献   

8.
Jun Yan  Tong Wei  Milin Zhang 《Carbon》2010,48(13):3825-3833
We present a quick and easy method to synthesize graphene-MnO2 composites through the self-limiting deposition of nanoscale MnO2 on the surface of graphene under microwave irradiation. These nanostructured graphene-MnO2 hybrid materials are used for investigation of electrochemical behaviors. Graphene-MnO2 composite (78 wt.% MnO2) displays the specific capacitance as high as 310 F g−1 at 2 mV s−1 (even 228 F g−1 at 500 mV s−1), which is almost three times higher than that of pure graphene (104 F g−1) and birnessite-type MnO2 (103 F g−1). Interestingly, the capacitance retention ratio is highly kept over a wide range of scan rates (88% at 100 mV s−1 and 74% at 500 mV s−1). The improved high-rate electrochemical performance may be attributed to the increased electrode conductivity in the presence of graphene network, the increased effective interfacial area between MnO2 and the electrolyte, as well as the contact area between MnO2 and graphene.  相似文献   

9.
Effects of MgO content (13.4–31.4 mol%) on the structure and properties of MgO-Al2O3-SiO2-F glass-ceramics were investigated by differential scanning calorimetry (DSC), X-ray diffractometry (XRD), infrared spectrophotometry (IR) and scanning electron microscopy (SEM). Results show that the main units of glass network structure are [SiO4] and [AlO4]. MgO contributes to the weakening of silica network and reduce the stability of glass structure. The main crystals of the MgO-Al2O3-SiO2-F glass-ceramics are phlogopite, spinel, flur-pargrasite and forsterite. The increase of reheating temperature and MgO content are beneficial to the separation of phlogopite crystal, and cause an higher aspect ratio of the phlogopite phase, which improves the machinability of the glass-ceramics. Excellent machinability is obtained when MgO content is 31.4 mol% at the processing temperature of 1100 °C for 2 h.  相似文献   

10.
Two kinds of functionalized graphene sheets were produced by thermal exfoliation of graphite oxide. The first kind of functionalized graphene sheets was obtained by thermal exfoliation of graphite oxide at low temperature in air. The second kind was prepared by carbonization of the first kind of functionalized graphene sheets at higher temperature in N2. Scanning electron microscopy images show that both two kinds of samples possess nanoporous structures. The results of N2 adsorption-desorption analysis indicate that both of two kinds of samples have high BET surface areas. Moreover, the second kind of functionalized graphene sheets has a relatively higher BET surface area. The results of electrochemical tests is as follows: the specific capacitance values of the first kind of functionalized graphene sheets in aqueous KOH electrolyte are about 230 F g−1; the specific capacitance values of the second kind of functionalized graphene sheets with higher BET surface areas are only about 100 F g−1; however, compared with the first kind of functionalized graphene sheets, the second kind has a higher capacitance retention at large current density because of its good conductive behaviors; furthermore, in non-aqueous EC/DEC electrolyte, the specific capacitance values of the first kind sample and the second kind sample are about 73 F g−1 and 36 F g−1, respectively.  相似文献   

11.
A novel nanostructured mesoporous CoxNi1−x layered double hydroxides (CoxNi1−x LDHs), which both Co(OH)2 and Ni(OH)2 exhibit, has been successfully synthesized by a chemical co-precipitation route using polyethylene glycol as the structure-directing reagent. Structural and morphological characterizations were performed using powder X-ray diffraction (XRD) and field emission scanning electron microscopy (FESEM). The component and thermal stability of the sample were measured by energy dispersed X-ray spectrometry (EDS), FT-IR and thermal analyses, including thermogravimetry (TG) and differential thermal analysis (DTA). Cyclic voltammogram and galvanostatic charge-discharge testified that the CoxNi1−x LDH has a specific capacitance of 1809 F g−1 at a current density of 1 A g−1 and remains at about 90.2% of the initial value after 1000 cycles at a current density of 10 A g−1. The relationship between the chemical composition and the capacitance is discussed.  相似文献   

12.
Multi-wall carbon nanotubes coated with polyaniline   总被引:3,自引:0,他引:3  
Multi-wall carbon nanotubes (CNT) were coated with protonated polyaniline (PANI) in situ during the polymerization of aniline. The content of CNT in the samples was 0-80 wt%. Uniform coating of CNT with PANI was observed with both scanning and transmission electron microscopy. An improvement in the thermal stability of the PANI in the composites was found by thermogravimetric analysis. FTIR and Raman spectra illustrate the presence of PANI in the composites; no interaction between PANI and CNT could be proved. The conductivity of PANI-coated CNT has been compared with the conductivity of the corresponding mixtures of PANI and CNT. At high CNT contents, it is not important if the PANI coating is protonated or not; the conductivity is similar in both cases, and it is determined by the CNT. Polyaniline reduces the contact resistance between the individual nanotubes. A maximum conductivity of 25.4 S cm−1 has been found with PANI-coated CNT containing 70 wt% CNT. The wettability measurements show that CNT coated with protonated PANI are hydrophilic, the water contact angle being ∼40°, even at 60 wt% CNT in the composite. The specific surface area, determined by nitrogen adsorption, ranges from 20 m2 g−1 for protonated PANI to 56 m2 g−1 for neat CNT. The pore sizes and volumes have been determined by mercury porosimetry. The density measurements indicate that the compressed PANI-coated CNT are more compact compared with compressed mixtures of PANI and CNT. The relaxation and the growth of dimensions of the samples after the release of compression have been noted.  相似文献   

13.
Polyaniline (PANI) (emeraldine) base has been exposed to iodine in an ethanol-water suspension. The conductivity of PANI increased from 10−9 S cm−1 to 10−4 S cm−1 already at the molar ratio [I2]/[PANI] = 1, and a higher content of iodine had only a marginal effect. This is the result of the protonation of PANI base with hydriodic acid, which is a by-product of the oxidation of the emeraldine form of PANI to pernigraniline constitutional units. The reaction is discussed on the basis of FTIR spectra. An alternative reaction, a ring-iodination of PANI, is marginal. Only one iodine atom substitutes a hydrogen atom in about 12 aniline units, even at high iodine concentration, [I2]/[PANI] = 8. The film of polyaniline base can be used in sensing iodine; after exposure to the iodine vapor, the conductivity of the polyaniline film increased.  相似文献   

14.
Electrochemical deposition of polyaniline (PANI) is carried out on a porous carbon substrate for supercapacitor studies. The effect of substrate is studied by comparing the results obtained using platinum, stainless steel and porous carbon substrates. PANI deposited at 100 mV s−1 sweep rate by potentiodynamic technique on porous carbon substrate is found to possess superior capacitance properties. Experimental variables, namely, concentrations of aniline monomer and H2SO4 supporting electrolyte are varied and arrived at the optimum concentrations to obtain a maximum capacitance of PANI. Low concentrations of both aniline and H2SO4, which produce PANI at low rates, are desirable. The PANI deposits prepared under these conditions possess network morphology of nanofibrils. Capacitance values as high as 1600 F g−1 are obtained and PANI coated carbon electrodes facilitate charge-discharge current densities as high as 45 mA cm−2 (19.8 A g−1). Electrodes are found to be fairly stable over a long cycle-life, although there is some capacitance loss during the initial stages of cycling.  相似文献   

15.
Poor crystallined α-MnO2 grown on multi-walled carbon nanotubes (MWCNTs) by reducing KMnO4 in ethanol are characterized by X-ray diffraction (XRD), scanning electron microscope (SEM) and Brunauer-Emmett-Telle (BET) surface area measurement, which indicate that MWCNTs are wrapped up by poor crystalline MnO2 and BET areas of the composites maintain the same level of 200 m2 g−1 as the content of MWCNTs in the range of 0-30%. The electrochemical performances of the MnO2/MWCNTs composites as electrode materials for supercapacitor are evaluated by cyclic voltammetry (CV) and galvanostatic charge-discharge measurement in 1 M Na2SO4 solution. At a scan rate of 5 mV s−1, rectangular shapes could only be observed for the composites with higher MWCNTs contents. The effect of additional conductive agent KS6 on the electrochemical behavior of the composites is also studied. With a fixed carbon content of 25% (MWCNTs included), MnO2 with 20% MWCNTs and 5% KS6 has the highest specific capacitance, excellent cyclability and best rate capability, which gives the specific capacitance of 179 F g−1 at a scan rate of 5 mV s−1, and remains 114.6 F g−1 at 100 mV s−1.  相似文献   

16.
The synthesis of polyaniline/platinum composites (PANI/Pt) has been achieved using both chemical and electrochemical methods. The direct chemical synthesis of PANI/Pt proceeds through the oxidation of aniline by PtCl62− in the absence of a secondary oxidant. SEM images of these samples indicate that the Pt particles are on the order of ∼1 μm for the chemically prepared composite. Electrochemical PANI/Pt synthesis is initiated by the uptake and reduction of PtCl62− into an a priori electrochemically deposited PANI film. This method produces a uniform dispersion of Pt particles with smaller particles with diameters ranging between 200 nm and 1 μm. The results indicate that electrochemical methods may be more suitable for controlling particle dimension. Both materials show reduced proton doping relative to PANI without Pt, indicating the metal particles directly influence proton doping and the oxidation state of the polymer. The electrochemical data indicate that the conductivity in solution is sufficient such that the normal acid doping is attainable for PANI/Pt produced using either synthetic method.  相似文献   

17.
Polyaniline (PANI) has been prepared by the oxidation of aniline with ammonium peroxydisulfate in the 0-4 M phosphoric acid. The maximum conductivity of PANI, 15.5 S cm−1, was found with PANI prepared in the presence of 1 M phosphoric acid. The mass loss after deprotonation with ammonium hydroxide revealed that relatively large amounts of phosphoric acid were associated with PANI if the polymerization had been carried out at higher acid concentration. This suggests the protonation of both the imine and amine nitrogens in PANI, the increased adsorption of phosphoric acid by PANI, or the presence of polyphosphate counter-ions. The increasing content of phosphoric acid is also reflected in the increase of sample density. FTIR spectra of ammonium salts collected after deprotonation proved that the counter-ions of the sulfate type, resulting from the decomposition of peroxydisulfate, always participated in the protonation of PANI. The proportion of sulfate to phosphate counter-ions was reduced as the concentration of phosphoric acid in the medium increased.Thin PANI films were produced in situ on glass surfaces immersed in the reaction mixture during the polymerization of aniline. Optical absorption has been used to assess their thickness, 70-140 nm, which was found to be virtually independent of the acid concentration. The film conductivity was comparable with the conductivity of the PANI powders produced at the same time. Colloidal dispersions were obtained when the reaction mixture contained poly(N-vinylpyrrolidone). The particle size, 200-260 nm, and polydispersity, determined by dynamic light scattering, were virtually independent of the concentration of phosphoric acid. The films produced on glass during the dispersion polymerization of aniline were thinner, 20-90 nm, compared with those grown in the precipitation polymerization.  相似文献   

18.
In this work, SiO2/Sb2O3 prepared by the sol-gel processing method, having a specific surface area, SBET, of 790 m2 g−1, an average pore diameter of 1.9 nm and 4.7 wt.% of Sb, was used as substrate base for immobilization of the 5,10,15,20-tetrakis(1-methyl-4-pyridyl)-21H,23H-porphine ion. Cobalt(II) ion was inserted into the porphyrin ring with a yield of complex bonded to the substrate surface of 59.4 μ mol g−1. A carbon paste electrode of this material was used to study, by linear sweeping voltammetric and chronoamperometric techniques, the electrocatalytic reduction of dissolved oxygen. The reduction, at the electrode solid-solution interface, occurred at −0.25 V versus SCE in 1.0 mol l−1 KCl solution, pH 5.5, by a four electron mechanism. The electrode response was invariant under various oxidation-reduction cycles showing that the system is chemically very stable. Such characteristics allowed the study of the electrode response towards various dissolved oxygen concentrations using the chronoamperometry technique. The cathodic peak current intensities plotted against O2 concentrations, between 1.0 and 12.8 mg l−1, showed a linear correlation. The electrode response time was very fast, i.e. about 1 s. This study was extended using the electrode to determine the concentration of dissolved oxygen in sea water samples.  相似文献   

19.
In studies of processes at oxidized compared with unoxidized electrode surfaces by transient methods corrections for double-layer charging are usually required and have often been made by extrapolation of double-layer capacitance (Cdl) data for the metallic surface, e.g. at Au or Pt, into the potential region of oxide-film formation. Voltammetry and impedance spectroscopy provide direct information on Cdl values determined at unoxidized, i.e. metallic, Au surfaces compared with those of anodic oxide films generated potentiostatically to various extents that are stable in time, and characterized by reductive linear-sweep voltammetry. Cdl is derived from constant-phase element (CPE) values and the CPE parameter, ?, which is near unity for most conditions. At oxidized Au surfaces Cdl depends on potential for various extents of oxide formation; it increases from 15 (±1) μF cm−2 at 1.75 V (RHE) to 25 (±1) μF cm−2 at 1.45 V (RHE) and is independent of added Cl or Br for concentrations 0-10−3 M of both anions, while, at unoxidized Au electrodes in the absence of halide anions, Cdl has a maximum value of 60 (±2) μF cm−2 at 0.80 V (RHE) and is now dependent on concentration of added Cl or Br ion. These major differences of Cdl for the oxidized and unoxidized Au surfaces indicate that double-layer charging corrections cannot be made simply by extrapolation of Cdl data for unoxidized Au metal surfaces into the potential region for oxide formation.  相似文献   

20.
Anatase titania nanotube arrays were fabricated by means of anodization of Ti foil and annealed at 400 °C in respective CO and N2 gases for 3 h. Electrochemical impendence spectroscopy study showed that CO annealed arrays possessed a noticeably lower charge-transfer resistance as compared with arrays annealed in N2 gas under otherwise the same conditions. TiO2 nanotube arrays annealed in CO possessed much improved lithium ion intercalation capacity and rate capability than N2 annealed samples. At a high charge/discharge current density of 320 mA g−1, the initial discharge capacity in CO annealed arrays was found to be as high as 223 mAh g−1, 30% higher than N2 annealed arrays, ∼164 mAh g−1. After 50 charge/discharge cycles, the discharge capacity in CO annealed arrays remained at ∼179 mAh g−1. The improved intercalation capacity and rate capability could be attributed to the presence of surface defects like Ti-C species and Ti3+ groups with oxygen vacancies, which not only improved the charge-transfer conductivity of the arrays but also possibly promoted phase transition.  相似文献   

设为首页 | 免责声明 | 关于勤云 | 加入收藏

Copyright©北京勤云科技发展有限公司  京ICP备09084417号