**2.1 The conducting polymers with metal and metal oxides nanomaterials**

1-D nanostructures of metal and metal oxides are of great importance for their electrical, optical, and catalytical properties as well as a wide range of applications in nanoelectronics and sensing devices [9, 10]. However, these nanostructures are very sensitive to air and moisture, which degrade the performance of the nanodevices. A polymer envelope would protect nanostructures from oxidation and corrosion, giving a good performance for a long time.

Nanostructured composites of silver nanowires with polypyrrole (Ag/PPY) have been prepared by the redox reaction in an aqueous solution at room temperature between silver nitrate and pyrrole using poly(vinyl pyrrolidone) (PVP) as assistant agent [11]. Under these conditions, a metallic nanowire coated with conducting polymer is formed. PVP is used both as a capping agent to form silver nanowires, and as a dispersant of pyrrole monomer. Silver nanowire is formed during silver nitrate reduction with pyrrole and monomer polymerizes on the surface of nanorode at the same time. A typical TEM image of these nanocables is shown in **Figure 1**.

*Conducting Polymer 1-D Composites: Formation, Structure and Application DOI: http://dx.doi.org/10.5772/intechopen.102484*

**Figure 1.** *TEM image of Ag/PPY nanocables (reproduced with permission from Ref. [11]).*

#### **Figure 2.**

*Schematic illustrations of the formation of the (a) silver nanowires@polypyrrole sponge (reproduced with permission from Ref. [12]) (b) silver nanowires@polypyrrole nanocomposite (reproduced with permission from Ref. [13]).*

The diameter of the layer is 50 nm, and the diameter of the silver core is 20 nm. The lengths of these nanocables are in the range of several to several tens' micrometers [11].

Recently, novel three-dimensional (3-D) silver nanowires@polypyrrole nanocomposites have been created [12, 13]. In the fabrication of the silver nanowires@polypyrrole sponge, the silver nanowires with the length of about 10 μm and diameter of 48.3 nm were synthesized trough solvothermal method and were used as the skeleton of the composite material. Polypyrrole was coated on the surface of silver nanowires by in situ chemical polymerization as shown in **Figure 2a** [12]. The prepared sponge exhibit good elasticity, mechanical strength and water absorption properties. The results showed that the complex permittivity and microwave absorption properties of the silver nanowires@polypyrrole sponge can be modulated by regulating the water amount. Another procedure 3-D core-shell silver nanowires@polypyyrole nanocomposite fabrication was proposed by Yuksel et al. [13]. Silver nanowires were prepared according to the polyol method and polypyrrole was synthesized using *in-situ* chemical polymerization (**Figure 2b**) [13]. These nanocomposites were applied for supercapacitors fabrication.

In addition to one-dimensional structures of silver and conducting polymer, 1-D composites of conducting polymers with copper and gold nanowires were also created. The combination of these nanowires and conducting polymer can endow new properties and exhibit synergistic effects of the nanocomposite components. For example, copper nanowires with polypyrrole [14] and polyaniline [15] have been prepared by a facile liquid-phase reduction with copper (II) chloride as precursor [14] and using a simple and reproducible approach by spontaneous chemisorption of polyaniline on the copper surface [15].

Composites containing conducting polymers with metal oxides such as ZnO, RuO2, MnO2, Co3O4, V2O5, MgO, Fe2O3, TiO2, and NiO have been produced. For example, Fan et al. [16] adopted an electrochemical polymerization method to assemble PANI and PEDOT on the surface of different oxides nanostructures including Co3O4, TiO2, and NiO nanowires, nanorods and nanoflakes. These metal oxides structures were fabricated by the hydrothermal method. The typical cyclic voltammetry (CV) curve of the TiO2/PANI nanorods on FTO (fluorine-doped tin oxide) glass is shown in **Figure 3a**. The first redox peaks A1 and C1 corresponds to the change between leucoemeraldine base and emeraldine salt with anion doping upon oxidation and dedoping upon reduction. The second pair of redox peaks A2 and C2 is due to the conversion between emeraldine base and pernigraniline salt. The change between emeraldine salt and emeraldine base does not involve an electron transfer process, and the redox peak is not reflected in the CV curve. Also, redox peaks of TiO2 are not observed in the studied potential range. The TiO2/PANI nanorods display interesting electrochromic properties. Namely, these nanorods show evident electrochromism with rich reversible color changes ranging from yellow for leucoemeraldine base, green for emeraldine salt, and blue for emeraldine-base to purple for pernigraniline salt under different applied potentials. In **Figure 3b** transmittance spectra are shown for different potentials applied to the electrode covered with a thin layer of composite. Moreover, the architecture of this material is well preserved after prolonged potential cycling, and does not show evident degradation (**Figure 3c**) [16].

Multicomponent 1-D nanostructures and conducting polymers have also been made. These materials can be tailored to exhibit, besides novel electrical, magnetic and optical properties, also good processing properties. For example, the composite of Co3O4@PPY@MnO2 "core-shell-shell" nanowires exhibited prominent electrochemical performance and remarkable long-term cyclic stability [17]. Co3O4 nanowire core backbone was grown on nickel foam by the hydrothermal and post-annealing method. Next, a conductive polypyrrole film was assembled on Co3O4 nanowire surface by potentiostatic deposition. The final product Co3O4@PPY@MnO2 was formed by soaking Co3O4@PPY in aqueous KMnO4. In this case, a redox reaction occurred in 3-D ordered nanowire interface. Such nanocomposites showed an effective pathway for

#### **Figure 3.**

*Electrochromic characterization of coaxial TiO2/PANI nanorods grown on FTO substrate: (a) CV curve in the potential range from 0.2 to 1 V at a scanning rate of 50 mV s<sup>1</sup> , (b) transmittance spectra of nanorods under different applied potentials, (c) SEM image nanorods after 5000 cycles (reproduced with permission from Ref. [16]).*

*Conducting Polymer 1-D Composites: Formation, Structure and Application DOI: http://dx.doi.org/10.5772/intechopen.102484*

**Figure 4.**

*SEM images of nanostructures grown in the AAO membrane (after the dissolution of AAO in 1 M NaOH for 1.5 h). (a) PANI fiber, (b–d) PANI/Au nanostructures for: (b) 1 h, (c) 1.5 h, (d) 2.5 h (reproduced with permission from Ref. [18]).*

fast electron transport and accelerates the reaction kinetics between the electroactive center and current collector.

It is also possible to deposit 1-D nanostructures of metal within or around a preformed polymer nanotube. Polyaniline nanotubes prepared using AAO template were coated with gold to form PANI/Au composite [18]. The morphology of these structures in a different stage of formation is shown in **Figure 4**.

The metallic phase can be also deposited within the polymeric nanotube structure. For example, cobalt nanowires were produced within the PANI tubes [19]. Such a system exhibits unique magnetic properties. Cobalt nanowires show greatly enhanced magnetic coercivity.

#### **2.2 The conducting polymers with carbon nanotubes or carbon fibers**

For the formation of 1-D composites containing conducting polymers, carbon nanotubes and carbon fibers was used as a carbon component of composites.

Synthesis of carbon nanotubes (CNTs) and conducting polymer composite was firstly reported by Ajayan et al. [20]. Since then, a lot of attention has been paid to the fabrication of such 1-D functional composite materials with desirable electrical and mechanical properties. Composites of single-walled carbon nanotubes (SWCNTs) or multi-walled carbon nanotubes (MWCNTs) with polyaniline have been the most intensively studied. For example, aniline has been polymerized on MWCNTs electrodes to obtain PANI films with novel surface characteristics including higher current densities and more effective polymerization [21]. Nanotube electrodes were constructed with whiskers of loosely packed MWCNTs. These nanotube whiskers with typical dimensions of 0.15 cm long and 0.028 cm in diameter were used as an electrode by attaching them to the tips of copper wire covered with conductive paint. Carbon nanotubes were prepared by the electric-arc process. The PANI films formed on the nanotube electrodes were prepared by electrochemical polymerization of aniline in H2SO4 solution. The morphology of polyaniline film deposited on carbon nanotube electrode and corresponding cyclic voltammetric response are shown in **Figure 5** [21].

Wu et al. [22, 23] have shown that the conductivity of MWCNTs/PANI composites received by *in-situ* chemical polymerization is 50–70% higher than that of the pure PANI. Whereas, with the increase of the MWCNTs nanotubes content to 24.8 wt% the conductivity increases by two orders of magnitude. Also, the change in the sign from positive to negative of the magnetoresistance at low temperatures is observed revealing the strong coupling between the carbon nanotubes and polyaniline in these

**Figure 5.**

*PANI film deposited on carbon nanotube electrode: (a) SEM image, (b) CV curves showing much larger background currents compared to the Pt electrode. Sweep rate used 20 mV s<sup>1</sup> . The geometrical area of the CNTs is 0.016 cm<sup>2</sup> compared to 0.16 cm<sup>2</sup> for the Pt electrode (reproduced with permission from Ref. [21]).*

composites. A similar effect on the conductivity of PANI was reported by Karim et al. [24]. They studied composite formed by deposition of PANI on the surface SWCNTs by using the *in-situ* chemical polymerization method [24]. The characterization of this material indicated that the conductivity and thermal stability of complex nanotubes were higher than polyaniline but lower than CNTs.

Many other conducting polymers such as PPY, PEDOT, and PTH were deposited onto the carbon nanotubes to form 1-D composites. Both *in-situ* and *ex-situ* chemical and electrochemical methods were used for polymer deposition. Similarly, such as polyaniline, these composites show considerably better electrochemical properties than that of the pristine polymer. The increase of polymeric phase conductivity (**Table 1**) and specific capacitance (**Table 2**) is observed for these materials.

There is also possible to incorporate conducting polymer into inside of carbon nanotubes. Steinmetz et al. [34] produced polyacetylene (PA) filled MWCNTs by *in-situ* polymerization using supercritical carbon dioxide (scCO2) and Ziegler-Natta catalyst. The supercritical fluid method can be also used to fill nanotubes with various


#### **Table 1.**

*Average values of conductivity of pure polymers and carbon nanotubes/polymer composites.*


**Table 2.**

*Average values of specific capacitance of pure polymers and carbon nanotubes/polymer composites.*

organic substances to polymerize photo-conducting poly(*N*-vinyl carbazole) (PNVC) and the conducting polypyrrole inside MWCNTs and double-walled carbon nanotubes (DWCNTs) [35]. MWCNTs and DWCNTs were opened by refluxing them in concentrated HNO3. The monomer together with an initiator was filled into these carbon nanotubes using scCO2. In the case of *N*-vinyl carbazole, 2,2<sup>0</sup> -azobis-isobutyronitrile (AIBN) was used as a monomer polymerization initiator, while polymerization of pyrrole was made using FeCl3 as the initiator of this process.

The structure and properties of composites of carbon 1-D nanomaterials and conducting polymers can be significantly improved by using well-organized structures of carbon nanotubes, such as aligned carbon nanotubes (ACNTs) network. In the case of ACNTs, the 1-D carbon cylinders are oriented in a parallel fashion perpendicular to the substrate. The aligned carbon nanotubes allow the polymer to be deposited on the walls of separated carbon nanotubes, limiting the thickness of the formed composite and the produced material has an open, and porous structure with a high surface area. Formation of ACNTs/conducting polymer composites was also carried out using both chemical and electrochemical polymerization. Feng et al. [36] aligned multi-walled carbon nanotubes (AMWCNTs) encapsulated by polyaniline by *in-situ* chemical polymerization. AMWCNTs grown on quartz glass sheet using catalytic pyrolysis. Next, these AMWCNTs were dipped in HCl solution containing aniline monomer for 12 h at 0°C. Aniline was adsorbed on the surface of the nanotubes. The polymerization process occurred after the addition dropwise of ammonium peroxydisulfate (APS) dissolved in HCl solution at 0°C for 4 h. **Figure 6** shows the preparation procedure for organizing AMWCNTs/PANI nanocomposite [36].

**Figure 6.**

*The preparation procedure of organizing AMWCNTs/PANI nanotubes (reproduced with permission from Ref. [36]).*

Compared to CNTs-based composites, carbon nanofibers (CNFs) have received much less attention as a component of 1-D composites, because CNTs have better mechanical properties, smaller diameter, and lower density than CNFs. However, because of their availability, relatively low price, and much easier production produce, carbon nanofibers are an excellent alternative to the more expensive carbon nanotubes [37]. Jang et al. [38] demonstrated that vapor deposition polymerization method could be effectively used for the introduction of polyaniline onto the carbon nanofibers. This process has allowed the formation of a uniform and ultrathin PANI layer of which the thickness-dependent on the amount of monomer (**Figure 7**). Besides, the increasing of PANI layer thickness results in CNFs significant increase in the specific capacitance of these composites. Good electrochemical properties are also observed for CNFs/PANI composites prepared by functionalizing carbon nanofibers with toluenediisocyanate trough amidation followed by reaction with an excess of aniline to form urea derivative and residual aniline, which was subsequently polymerized and grafted with a urea derivative [39].

Recently, graphene nanoribbons were used to make nanocomposites with polypyrrole [40]. Graphene nanoribbons were synthesized by unzipping and exfoliation of MWCNTs, while polypyrrole was prepared using a chemical polymerization process in the presence of graphene oxide nanoribbons. These nanocomposites had a

#### **Figure 7.**

*SEM: (a and b),TEM: (c–e), images of pristine CNFs (a), and CNFs/PANI nanocomposites (b–e) with different the thickness of PANI layer deposited on the CNFs controlled by changing the amount of monomer: (c) 0.05 ml, (b) 0.1 ml, (c) 0.2 ml (reproduced with permission from Ref. [38]).*

higher surface area than pure polypyrrole, which improved the charge storage capacity of the nanocomposites.

#### **2.3 The other 1-D nanocomposites**

To enhance processability, electrochemical, thermal, and mechanical stability, conducting polymers are often combined with other 1-D nanostructures, such as semiconducting materials, crystals of metalloorganic complexes.

Similar to the preparation of 1-D metal or metal oxide/conducting polymer nanocomposites, semiconducting selenides and sulfides can be incorporated into conducting polymers trough chemical or electrochemical methods. Alivisatos et al. [41] obtained CdSe/poly-3(hexylthiophene) (P3HT) nanorods. CdSe nanorods were dispersed with P3HT in a mixture of pyridine and chloroform and spin-cast to create a uniform film consisting of dispersed nanorods in the polymer. Such material was used to fabricate efficient hybrid solar cells with an external quantum efficiency of over 54% and monochromatic power conversion efficiency of 6.9%. Template techniques of synthesis 1-D nanomaterials, have been demonstrated for the preparation of sulfides with conducting polymers. Thus, Lin et al. [42] reported the preparation of CdS/ PANI coaxial nanocables by the electrochemical synthesis in the AAO membrane. The diameter of the CdS nanowires was about 70 nm, which was the same as the pore diameter of the AAO membrane. The outer diameter of the PANI was about 90 nm. Guo et al. [43] synthesized CdS/PPY heterojunction nanowires by template technique using also porous AAO membrane. These nanowires had a smooth surface with diameters in the range of 200–400 nm. In addition to the template technique, an *in-situ* polymerization at the interfacial layer between chloroform and water has been developed for the preparation of Cu2S nanorods coated with polypyrrole layer [44]. Smooth and uniform coaxial Cu2S/PPY nanocables have been fabricated by controlling the reaction conditions, such as the molar ratio of pyrrole to oxidant and concentration of pyrrole in chloroform. The thickness of the PPY layer on the surface of Cu2S nanorods depends on the polymerization time (**Figure 8**). The hydrothermal reaction was also applied to prepare Bi2S3/PPY nanocomposites [45]. The PPY coating on the surface Bi2S3/PPY nanorods was smooth and uniform in thickness.

1-D nanocrystals and conducting polymer composites were also created. Crystals of β-akaganeite (β-Fe3+O(OH,Cl)) with PEDOT [46, 47] and crystals of iridium complex ([IrCl2(CO)2] ) with PPY [48] are examples of 1-D composites containing conducting

#### **Figure 8.**

*TEM images of Cu2S/PPY nanorods were obtained with a pyrrole polymerization time of: (a) 1 h, (b) 2 h, (c) 3.5 h, (d) 5 h. inset of (B): SAED of the single Cu2S/PPY nanorod (reproduced with permission from Ref. [44]).*

#### **Figure 9.**

*SEM and inset TEM images of: (a) PEDOT/β-Fe3+O(OH,Cl) nanospindles (reproduced with permission from Ref. [46]), and (b) 1-D-IrCl2(CO)2/PPY nanocomposites (reproduced with permission from Ref. [48]).*

polymer and crystal metalloorganic complexes. The advantage of fabrication of these materials is the possibility of their preparation by *in-situ* one-step or two-step approach, respectively. Namely, PEDOT/β-Fe3+O(OH,Cl) nanospindles (**Figure 9a**) were synthesized in an aqueous solution trough one-step chemical oxidation polymerization using monomer EDOT, and FeCl3∙6H2O as an oxidant in the presence of CTAB and poly (acrylic acid) (PAA). Under these conditions, the polymerization of EDOT, and the hydrolyzation of FeCl3 to form β-Fe3+O(OH,Cl) occur at the same time, leading to the formation PEDOT/β-Fe3+O(OH,Cl) nanocomposite [46, 47]. The 1-D-IrCl2(CO)2/PPY nanocomposites (**Figure 9b**) were synthesized in a dichloromethane solution by *in-situ* two-step electrodeposition. First, needles of the iridium complex were prepared by electrochemical oxidation of (AsPh4)[IrCl2(CO)2]. Next, pyrrole was electropolymerized on the surface of the iridium needles [48]. Both the crystals size and thickness of the polymer can be easily controlled very simply using the reaction conditions such as concentration of compounds, different reaction times, and kind of solvent.
