Supercapacitor carbon/conducting polymer composite

The enhancement of specific capacitance for carbon materials is generally realized by the usage of pseudocapacitance effects, which depend on the surface functionality of carbon and on the presence of electro-active species (termed supercapacitors) [162-164]. Several modifications (i.e., oxidation of carbon for increasing the surface functionality, formation of carbon/conducting polymers composites or insertion of electroactive particles of transition metals) can be carried out to increase the pseudocapacitance that arises fi om faradaic reactions. However, the enhancement of the capacitance connected with faradaic reactions of surface groups often contributes to an increase in the self-discharge of the capacitor due to the instability of the functionalities [165]. 

Peng, C., Zhang, S., Jewell, D., Chen, G.Z., 2008. Carbon nanotube and conducting polymer composites for supercapacitors. Prog. Nat. Sci. 18, 777-788. 

Yang, Q., S. K. Pang, and K. C. Yung. 2014. Study of PEDOT-PSS in carbon nanotube/ conducting polymer composites as supercapacitor electrodes in aqueous solution. Journal of Electroanalytical Chemistry 728 140-147. 

Electronically conducting polymers (ECPs) such as polyaniline (PANI), polypyrrole (PPy) and po 1 y(3.4-cthy 1 cncdi oxyth iophcnc) (PEDOT) have been applied in supercapacitors, due to their excellent electrochemical properties and lower cost than other ECPs. We demonstrated that multi-walled carbon nanotubes (CNTs) prepared by catalytic decomposition of acetylene in a solid solution are very effective conductivity additives in composite materials based on ECPs. In this paper, we show that a successful application of ECPs in supercapacitor technologies could be possible only in an asymmetric configuration, i.e. with electrodes of different nature. 

In the past five years, many ion conducting polymers and gel electrolytes have been investigated for EDLC application. Figure 15 shows the capacities of various carbon electrodes in SPE or gel electrolytes. The values listed in this figure do not satisfy the requirements for EV. However, it is expected that the requirements of supercapacitors for EV can be achieved by development of devices based on composite electrodes and gel electrolyte systems as described in this chapter. 

Rakhi et al reported the conducting-polymers (polyaniline [PANI] and PPy)-coated carbon nanocoils (CNCs) as efficient binder-free electrode materials for supercapacitors for the first time, in which the CNCs acted as a perfect backbone for the uniform distribution of the conducting polymers in the composites [16]. Ihe SC and maximum storage energy per unit mass of the composites were found to be comparable to one of the best-reported values for polymer-coated MWNTs. Dumanli et al. prepared the chemically bonded carbon nanofibers (CNFs)-PPy composite via electro-polymerization of Py on CNFs [17]. It showed that the final capacitance values were highly dependent on the number of deposition cycles and deposition rates. The best result for the coiled CNF-PPy composite system was found to be 27.6 C/cm at six times cycling using 25 mV/s. 

Metal oxide-based materials, carbon materials, and conducting polymers for electrochemical supercapacitor electrodes have been reviewed in detail (6). Two important future research directions have been summarized The development of composite and nano-structured electrochemical supercapacitor materials to overcome the problem of low energy density of electrochemical supercapacitors. 

Composites Based on Conducting Polymers and Carbon Nanotubes for Supercapacitors... 

---