Polyaniline in various forms has been widely explored as an electrode material for supercapacitors due to its high theoretical charge storage capacity, facile-cost-effective synthesis, good mechanical strength and ultrafast charge transport. However, commercialization of such pristine forms is very much restricted by low solubilities, rapid agglomeration during device design accompanied by poor electrochemical life and fast environmental decomposition. The blending with nano-carbon materials, metal oxides and other competent materials, may result in high quality materials– “nanocomposites” with superior features is ideally fit for future generation energy storage devices. The present chapter deals with detailed discussions on designing, the fabrication of such binary and ternary nanocomposites, correlating their morphology with electrochemical behavior, so as to optimize their supercapacitive performances. Such an attempt would help to outline the present status and future aspects of these materials which will be of first-hand assistance especially to the beginners to this field of research.
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As reviewed in the previous chapter, Polyaniline (PANI) has high potentiality as supercapacitor electrode material and very recently, it has been able to achieve specific capacitance as high as 950 Fg-1 through the involvement of the entire volume in storage of charge, surpassing other conducting polymers that store charge solely on surface (Wang, Huang & Wei, 2010) (Nguyen & Yoon, 2016). However, the theoretically calculated utmost specific capacitance value of PANI is 2000 Fg-1, although the experimental values evaluated by different methodologies are considerably inferior to the predicted value as only a small percentage of PANI make effective contribution to the total capacitance which is again dependent on both – its conductivity state (percentage of emeraldine salt) and extent of counter-anions diffusion through it (Li, Wang & Chu, 2009). Moreover, pseudocapacitive processes of PANI in most cases involve swelling, shrinkage and cracking of the polymer skeleton during doping-dedoping-redoping process, leading to poor GCD cycle efficiency. In addition, at higher applied potentials PANI degradation may result due to over-oxidation, which reduces the electrical conductivity as well as working potential window for pristine PANI electrodes. Furthermore, addressing of the following key issues: (i) ordered and well-aligned morphology; (ii) optimization of doping level for superior charge transport; (iii) introduction and maintenance of porous-structure for large number of stable galvanostatic charging/discharging cycles; is crucial for upgrading the current device-performances. These problems necessitate the development of “nanocomposite” fabrication that combine PANI with other materials such as nano-carbonaceous systems or nano-metal oxides for improving the overall electrochemical and mechanical stability as well as energy storage capacity of the “supercap” electrodes (Yin, Liu & Fan, 2012) (Beidaghia & Gogotsi, 2014) (Shukla, Banerjee & Ravikumar, 2012) (Wu, Chu & Hu, 2013).
The present chapter deals with detailed discussion on fabrication and designing of binary nanocomposites with nano-carbon based systems as well as nano-morphology based-metal oxides and other non-trivial pseudocapacitive substances, correlating the composites’ morphology with their electrochemical behavior, so as to bring out the optimum requirements for desired performances. In addition to these two-component nanocomposites, discussion on recently developed ternary-nanocomposites composed of either metal oxide with strong pseudocapacitance and/or a high surface area porous-carbon to act as suitable substrate to anchor the pseudocapacitive materials, and nanophased-PANI as the common material have been carried out in details. These novel systems have become attractive candidates for the developing new-generation supercapacitors. The motivation is that all the three components would contribute synergistically to the overall specific capacitance, making-up their disadvantages so as to achieve superior electrical conductivity, larger active-surface area, and enhanced electrochemically-active redox sites accessibility for improving the device performances.