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A facile synthesis of polypyrrole/carbon nanotube composites with ultrathin, uniform and thickness-tunable polypyrrole shells.

Zhang B, Xu Y, Zheng Y, Dai L, Zhang M, Yang J, Chen Y, Chen X, Zhou J - Nanoscale Res Lett (2011)

Bottom Line: An improved approach to assemble ultrathin and thickness-tunable polypyrrole (PPy) films onto multiwall carbon nanotubes (MWCNTs) has been investigated.The coated PPy films can be easily tuned by adding ethanol and adjusting a mass ratio of pyrrole to MWCNTs.Moreover, the thickness of PPy significantly influences the electronic conductivity and capacitive behavior of the PPy/MWCNT composites.

View Article: PubMed Central - HTML - PubMed

Affiliation: Key Lab Polymer Composite & Funct Mat, Key Lab Designed Synth & Applicat Polymer Mat, School of Chemistry and Chemical Engineering, Sun Yat-Sen University, Guangzhou, 510275, China. lzdai@xmu.edu.cn.

ABSTRACT
An improved approach to assemble ultrathin and thickness-tunable polypyrrole (PPy) films onto multiwall carbon nanotubes (MWCNTs) has been investigated. A facile procedure is demonstrated for controlling the morphology and thickness of PPy film by adding ethanol in the reaction system and a possible mechanism of the coating formation process is proposed. The coated PPy films can be easily tuned by adding ethanol and adjusting a mass ratio of pyrrole to MWCNTs. Moreover, the thickness of PPy significantly influences the electronic conductivity and capacitive behavior of the PPy/MWCNT composites. The method may provide a facile strategy for tailoring the polymer coating on carbon nanotubes (CNTs) for carbon-based device applications.

No MeSH data available.


Related in: MedlinePlus

Capacitance values of CNT/PPy composites. (A) Specific capacitance of PPy/MWCNT composites with different PPy thickness. The insets are CV curves of PPy/MWCNT composites with various PPy thickness (nm): 6, 15, 21, 28, 37, 51 and 100 nm in 1 M KCl solution at scanning rate of 100 mVs-1. (B) PPy thickness dependence of the charge transfer resistance of PPy/MWCNT composites. The insets are EIS curves of PPy/MWCNT composites with different PPy thickness.
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Figure 7: Capacitance values of CNT/PPy composites. (A) Specific capacitance of PPy/MWCNT composites with different PPy thickness. The insets are CV curves of PPy/MWCNT composites with various PPy thickness (nm): 6, 15, 21, 28, 37, 51 and 100 nm in 1 M KCl solution at scanning rate of 100 mVs-1. (B) PPy thickness dependence of the charge transfer resistance of PPy/MWCNT composites. The insets are EIS curves of PPy/MWCNT composites with different PPy thickness.

Mentions: Furthermore, the electrochemical properties of the PPy/MWCNT composites compared with pristine MWCNTs and pure polypyrrole were evaluated by cyclic voltammetry test. As shown in Figure S3-A in Additional file 1 the electrochemical properties of the PPy/MWCNT composite which the thickness of PPy shell is 6 nm have been obtained by cyclic voltammetry [CV] with different scan rates. They all show the typical double-layer capacity behavior, which benefited from their large surface area [38-41]. It can be found that the CV curves of PPy/MWCNT composite are rectangle-shaped, resulting from a very quick charging/discharging process in PPy/MWCNT composite [32]. Compared with the CV curves of PPy/MWCNT composites, CV curves of both pure PPy and MWCNTs show lower specific capacitance and non-rectangle-shape. Thus it can be confirmed that the electrochemical properties of PPy/MWCNT composites are superior than those of the individual component PPy or MWCNT. (Figures S3-B and S3-C in Additional file 1) [8,42] This can be attributed to the special structure and morphology of the MWCNT-PPy core-shell composite. The long-term cycle stability of the PPy/MWCNT composite with the thickness of 6 nm was also evaluated by repeating the CV test at a scan rate of 200 mVs-1 for 1000 cycles. (Figure S4 in Additional file 1) The PPy/MWCNT electrode exhibits excellent stability over the entire cycle numbers and maintains 73.6% of its initial capacity after 1000 cycles, which is consistent with that reported in the previous literature [38-41]. Swelling and shrinkage of electrochemically active conducting polymers is well known and may lead to degradation of the electrode during cycling. This has been overcome by the core-shell structures, which maybe benefit from the strong interaction between CNT and PPy[38-41]. After several 1000 cycles, the interaction force between CNT and PPy remains unchanged and the PPy shell appears to have a dense sheet structure, which implies that the transfer ability of charges remains fairly constant. Hence, it could be considered that an interesting synergistic effect between MWCNT and PPy plays an important role in the electrochemical charge-discharge process. Firstly, the core-shell structure leads to an increase in the surface area of the PPy/MWCNT composite, which enhances MWCNTs solubility and dispersibility and improves effectively the contact with the electrode and electrolyte. Secondly, the conductivity of the MWNTs dispersed throughout the structure increases the electrical conductivity of the composite film over the entire PPy redox cycle. Thirdly, the ultrathin PPy shell could effectively shorten the transport path of ion diffusion through the solid phase and decrease the contact resistance between the polymer and CNT, which can significantly improve the charge transfer ability between the polymer shell and CNT[8,39]. Therefore, the relationship between the thickness of PPy and the electrical properties of the PPy/MWCNT composites should be taken into account. The specific capacitance values of CNT/PPy composites with different PPy thickness from 6 nm to 100 nm (including 6, 15, 21, 28, 37, 51, and 100 nm) are presented in Figure. 7A. [Note: In order to collect solid data, for every single sample, we fabricate three electrodes to do the measurements and the average values with error bar are presented in both Figures 7Aand 6Baccordingly] Clearly, the specific capacitance decreases linearly as the thickness of polymer shell increases. However, when the PPy thickness reaches 28 nm, the nonlinear decrease of the specific capacitance with the increase of PPy thickness is clear. As shown in Figure 7A, the specific capacitance of the PPy/CNT composites decreases with the increase of PPy thickness and the trend is intensified when the PPy thichness is thicker than about 30 nm. Generally, for an ideal electrode material, the response current rapidly reaches a steady-state value due to its high electrical conductivity when the sweep direction of potential is changed, leading to rectangular-shaped CV curves. Hence, the current/potential slope at the switching potentials can be used to qualitatively reflect a magnitude of the active electrode material's conductivity; the steeper the slope, the higher the conductivity[43]. From Figure 7A, the CV curves are not rectangle-shaped gradually at a sweep rate of 100 mVs-1 as the increase of PPy thickness, indicating the resistance-like electrochemical behavior[35]. In the conducting polymer composites, the conductivity depends not only on the doping level or conjugated length but also on some external factors such as the compactness of the sample or orientation of the microparticles [42,43]. Based on this analysis, the change of the electrical performance of the PPy/CNT composite may relate to the synergistic effect of these factors aforesaid. Nevertheless, the beneficial effect will reduce with the increase of the ratio of PPy:CNT. This may be because the thick PPy shell is too compact to hinder counterions entering into/ejecting from the PPy films to reach the surface of CNT.


A facile synthesis of polypyrrole/carbon nanotube composites with ultrathin, uniform and thickness-tunable polypyrrole shells.

Zhang B, Xu Y, Zheng Y, Dai L, Zhang M, Yang J, Chen Y, Chen X, Zhou J - Nanoscale Res Lett (2011)

Capacitance values of CNT/PPy composites. (A) Specific capacitance of PPy/MWCNT composites with different PPy thickness. The insets are CV curves of PPy/MWCNT composites with various PPy thickness (nm): 6, 15, 21, 28, 37, 51 and 100 nm in 1 M KCl solution at scanning rate of 100 mVs-1. (B) PPy thickness dependence of the charge transfer resistance of PPy/MWCNT composites. The insets are EIS curves of PPy/MWCNT composites with different PPy thickness.
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Figure 7: Capacitance values of CNT/PPy composites. (A) Specific capacitance of PPy/MWCNT composites with different PPy thickness. The insets are CV curves of PPy/MWCNT composites with various PPy thickness (nm): 6, 15, 21, 28, 37, 51 and 100 nm in 1 M KCl solution at scanning rate of 100 mVs-1. (B) PPy thickness dependence of the charge transfer resistance of PPy/MWCNT composites. The insets are EIS curves of PPy/MWCNT composites with different PPy thickness.
Mentions: Furthermore, the electrochemical properties of the PPy/MWCNT composites compared with pristine MWCNTs and pure polypyrrole were evaluated by cyclic voltammetry test. As shown in Figure S3-A in Additional file 1 the electrochemical properties of the PPy/MWCNT composite which the thickness of PPy shell is 6 nm have been obtained by cyclic voltammetry [CV] with different scan rates. They all show the typical double-layer capacity behavior, which benefited from their large surface area [38-41]. It can be found that the CV curves of PPy/MWCNT composite are rectangle-shaped, resulting from a very quick charging/discharging process in PPy/MWCNT composite [32]. Compared with the CV curves of PPy/MWCNT composites, CV curves of both pure PPy and MWCNTs show lower specific capacitance and non-rectangle-shape. Thus it can be confirmed that the electrochemical properties of PPy/MWCNT composites are superior than those of the individual component PPy or MWCNT. (Figures S3-B and S3-C in Additional file 1) [8,42] This can be attributed to the special structure and morphology of the MWCNT-PPy core-shell composite. The long-term cycle stability of the PPy/MWCNT composite with the thickness of 6 nm was also evaluated by repeating the CV test at a scan rate of 200 mVs-1 for 1000 cycles. (Figure S4 in Additional file 1) The PPy/MWCNT electrode exhibits excellent stability over the entire cycle numbers and maintains 73.6% of its initial capacity after 1000 cycles, which is consistent with that reported in the previous literature [38-41]. Swelling and shrinkage of electrochemically active conducting polymers is well known and may lead to degradation of the electrode during cycling. This has been overcome by the core-shell structures, which maybe benefit from the strong interaction between CNT and PPy[38-41]. After several 1000 cycles, the interaction force between CNT and PPy remains unchanged and the PPy shell appears to have a dense sheet structure, which implies that the transfer ability of charges remains fairly constant. Hence, it could be considered that an interesting synergistic effect between MWCNT and PPy plays an important role in the electrochemical charge-discharge process. Firstly, the core-shell structure leads to an increase in the surface area of the PPy/MWCNT composite, which enhances MWCNTs solubility and dispersibility and improves effectively the contact with the electrode and electrolyte. Secondly, the conductivity of the MWNTs dispersed throughout the structure increases the electrical conductivity of the composite film over the entire PPy redox cycle. Thirdly, the ultrathin PPy shell could effectively shorten the transport path of ion diffusion through the solid phase and decrease the contact resistance between the polymer and CNT, which can significantly improve the charge transfer ability between the polymer shell and CNT[8,39]. Therefore, the relationship between the thickness of PPy and the electrical properties of the PPy/MWCNT composites should be taken into account. The specific capacitance values of CNT/PPy composites with different PPy thickness from 6 nm to 100 nm (including 6, 15, 21, 28, 37, 51, and 100 nm) are presented in Figure. 7A. [Note: In order to collect solid data, for every single sample, we fabricate three electrodes to do the measurements and the average values with error bar are presented in both Figures 7Aand 6Baccordingly] Clearly, the specific capacitance decreases linearly as the thickness of polymer shell increases. However, when the PPy thickness reaches 28 nm, the nonlinear decrease of the specific capacitance with the increase of PPy thickness is clear. As shown in Figure 7A, the specific capacitance of the PPy/CNT composites decreases with the increase of PPy thickness and the trend is intensified when the PPy thichness is thicker than about 30 nm. Generally, for an ideal electrode material, the response current rapidly reaches a steady-state value due to its high electrical conductivity when the sweep direction of potential is changed, leading to rectangular-shaped CV curves. Hence, the current/potential slope at the switching potentials can be used to qualitatively reflect a magnitude of the active electrode material's conductivity; the steeper the slope, the higher the conductivity[43]. From Figure 7A, the CV curves are not rectangle-shaped gradually at a sweep rate of 100 mVs-1 as the increase of PPy thickness, indicating the resistance-like electrochemical behavior[35]. In the conducting polymer composites, the conductivity depends not only on the doping level or conjugated length but also on some external factors such as the compactness of the sample or orientation of the microparticles [42,43]. Based on this analysis, the change of the electrical performance of the PPy/CNT composite may relate to the synergistic effect of these factors aforesaid. Nevertheless, the beneficial effect will reduce with the increase of the ratio of PPy:CNT. This may be because the thick PPy shell is too compact to hinder counterions entering into/ejecting from the PPy films to reach the surface of CNT.

Bottom Line: An improved approach to assemble ultrathin and thickness-tunable polypyrrole (PPy) films onto multiwall carbon nanotubes (MWCNTs) has been investigated.The coated PPy films can be easily tuned by adding ethanol and adjusting a mass ratio of pyrrole to MWCNTs.Moreover, the thickness of PPy significantly influences the electronic conductivity and capacitive behavior of the PPy/MWCNT composites.

View Article: PubMed Central - HTML - PubMed

Affiliation: Key Lab Polymer Composite & Funct Mat, Key Lab Designed Synth & Applicat Polymer Mat, School of Chemistry and Chemical Engineering, Sun Yat-Sen University, Guangzhou, 510275, China. lzdai@xmu.edu.cn.

ABSTRACT
An improved approach to assemble ultrathin and thickness-tunable polypyrrole (PPy) films onto multiwall carbon nanotubes (MWCNTs) has been investigated. A facile procedure is demonstrated for controlling the morphology and thickness of PPy film by adding ethanol in the reaction system and a possible mechanism of the coating formation process is proposed. The coated PPy films can be easily tuned by adding ethanol and adjusting a mass ratio of pyrrole to MWCNTs. Moreover, the thickness of PPy significantly influences the electronic conductivity and capacitive behavior of the PPy/MWCNT composites. The method may provide a facile strategy for tailoring the polymer coating on carbon nanotubes (CNTs) for carbon-based device applications.

No MeSH data available.


Related in: MedlinePlus