Elsevier

Energy Storage Materials

Volume 33, December 2020, Pages 336-359
Energy Storage Materials

Polyindole batteries and supercapacitors

https://doi.org/10.1016/j.ensm.2020.08.010Get rights and content

Abstract

Polyindole (Pind) is one of the rising conducting polymers (CPs) finding application in energy, sensors, biomedicine, corrosion protection, and catalysis. Pind and its composites of carbon, metal oxides and transitional metal dichalcogenides are gaining enormous attention as electrodes in batteries and supercapacitors. Herein, the methods to synthesize (polymerize) and utilize Pind-based electrodes in batteries and supercapacitors are systematically reviewed. A critical perspective and future works to be done to push the performance of these electrodes for electrochemical energy storage are also discussed.

Introduction

The first attempt to observe electrical conductivity from organic polymers dates back in the 1970s when Shirakawa, Heeger and MacDiarmid group doped polyacetylene with halogen vapors of chlorine, bromine, or iodine [1]. This was an incredible discovery as it meant that the widely known insulating materials (the polymers) could be made conductive. A Nobel Prize in chemistry was later awarded to them in 2000 for their discovery [2]. To this date, conducting polymers (CPs) and their constituent composites have attracted enormous research attention for use in various applications such as energy [3], [4], [5], [6], biomedicine [5,7,8], sensors [9], [10], [11], [12], corrosion protection [13], [14], [15], [16] and many others. The widely anticipated applications have led to the discovery of various other CPs including; polypyrrole (Ppy) [17], [18], [19], [20], polyaniline (Pani) [21], [22], [23], polyindole (Pind) [24], polythiophene [25,26], poly(3,4-ethylenedioxythiophene) polystyrene sulfonate (PEDOT:PSS) [27,28], and many others together with their substituted derivatives. CPs exhibit tuneable conductivity, excellent capacitive properties, have relatively simple components (such as C, H, N or S), and are very easy to synthesize. These properties make CPs reliable material sources for their voted applications, especially in electrochemical energy storage.

The most commonly studied electrochemical energy storage devices include batteries and supercapacitors [29], [30], [31], [32], [33], [34], [35]. The fundamental difference between the two devices is in their performance [36]. Batteries show relatively high energy density (150–200 W h/kg) but low power density (less than 1000 W/kg), while supercapacitors exhibit a high power density (greater than 10 kW/kg) and an increased lifespan (104–105 cycles), but reduced energy density (less than 10 W h/ kg) [37]. Therefore, the applications of the two storage devices tend to vary due to the amount of charge, which can be possibly delivered by each, in a specific time period. The common electrode materials for batteries and supercapacitors include; carbon-based materials [38], [39], [40] (such as carbon nanotubes (CNTs), graphene, carbon black (CB), activated carbon, etc.), electroactive 2D materials [41,42] and transition metal hydro (oxides) [43,44] (such as MXene, RuO2, MnO2, Co3O4, NiO, Co(OH)2, Ni(OH)2), metal–organic frameworks (MOFs) [45,46], etc.), ion-exchange, conducting, and redox-active polymers [47](such as Pani, Ppy, Pind, PEDOT:PSS, and their derivatives, etc.). Carbon-based electrodes have high conductivity, excellent chemical and cycling stability and high-power density [48], [49], [50], [51], [52]. However, the energy density of carbon-based electrodes is usually low as compared to CPs and some transition metal hydro (oxides), which have a high energy density but limited power density [53], [54], [55]. This is due to the carbon materials’ energy storage mechanism which depends much on the material's surface area [56], [57], [58]. Moreover, transition metal hydro (oxides) have problems like low conductivity, high cost and limited natural abundance [59], [60], [61], [62], [63], [64]. In contrast, CPs demonstrate increased charge storage efficiencies as active electrode materials, with competitive charge-discharge abilities and increased lifecycles due to their ability to utilize the reversible redox reactions at the electrode surfaces [29,65]. In addition, CPs show high conductivity, high charge storage ability, wide voltage window, ease of synthesis, low cost, and environmental friendliness. These properties make CPs suitable materials for the fabrication of electrodes for electrochemical energy storage applications [[29], [30], [31], [32], [33], [34],66].

The commonly studied CPs for energy storage applications are Pani [67], [68], [69] and Ppy [67,70] with Pind quickly starting to catch research attention in this field (Fig. 1A). Pind is interesting because of many factors. The properties of poly (para-phenylene) and Ppy can all be self-possessed by Pind [71]. This is because indole has a fused aromatic molecular structure which gives Pind a structure similar to that of Ppy and poly (para-phenylene) (Fig. 1B) [71], [72], [73], [74], [75]. Ppy has good electrical conductivity, environmental stability, good cycling stability [76,77]. In addition, Poly (para-phenylene) on the other hand, has the advantage of excellent thermal stability [73]. When employed in energy storage applications, Pind shows a slow hydrolytic degradation (as compared to Pani), competitive redox potential (as compared to Ppy) [78], high cycling and thermal stability [24,79] making it superior for energy storage for long run [80]. In addition, Pind does not involve the formation of any salt during complete charged or discharges phase, such as leucoemeraldine and pernigraniline as it is a common case with Pani [81]. This reduces the resistance which would have been offered by these salts and results in increased internal conductivity of Pind [82]. However, the conductivity of Pind is less by two orders of magnitude compared with that of Pani and Ppy, though as good as the two in both environmental and electrochemical stability [83]. Other Pind properties include high stable redox activity [84], good photoluminescent properties [85], fast switchable electrochromic ability [84,86,87] and air-stable electrical conductivity in the doped state [88]. With these properties, Pind is emerging as a good candidate for applications in various domains, such as organic electronics [79], electrocatalysis/catalysis [89,90], batteries and supercapacitors [91,92], anti-corrosion coatings [93] and sensors [94].

Having provided a brief introduction about CPs, batteries, supercapacitors and Pind, we now focus strictly on Pind in our next sections with its application in batteries and supercapacitors as an active electrode material. The next sections are as follows; Section 2 describes the synthesis (polymerization) procedures of Pind, Section 3 discusses the characterization of Pind, Section 4 reviews the applications of Pind and Pind-based composites in supercapacitors and batteries. Section 5 provides the outlook and conclusions with regards to Pind and its applications for future energy storage.

We explicitly note that only two articles have tried to summarize Pind-related literature. The article from Zhou et al. [24] attempted to review the overall progress of Pind research with reference to its synthesis, polymerization mechanisms, properties, and applications. In their review, the applications of Pind in electrochemical energy storage was made brief, since they attempted to cover many different topics. Another article is from Mudila et al. [92] which summarized only some of the Pind supercapacitors. The article was made brief, did not highlight most of the interesting recent works and lacked depth with regards to articulating the direction of innovation of Pind supercapacitors. This article is different from those two in that it focuses on batteries and supercapacitor electrodes of Pind and in a much detailed approach.

Section snippets

Synthesis of Pind

The synthesis of Pind is carried out via various polymerization routes including; chemical oxidative polymerization [71,74,[95], [96], [97], [98]], electrochemical polymerization [79,94,99,100] and emulsion polymerization [101], [102], [103]. These polymerization methods are capable of giving Pind with different morphologies including; nanowires [104], [105], [106], nanorods [103,107], nano- and micro-fiber [85,108], nano- and micro-spheres [96,98,101,103,109], and nanobelts [105]. Table 1

Morphology

The characteristic SEM morphologies of Pind CP is provided in Table 1. It can range from nanowires, nanorods, nano- and micro-fibers, nano- and micro-spheres, to crystalline nanobelts, all depending on the synthesis technique employed. The named physical structures can exist in agglomerated morphologies with smooth surfaces [85,96,98,101,[103], [104], [105], [106], [107], [108], [109]]. The agglomerated morphologies are due to the involved solution stages of Pind synthesis which usually involve

Characterization and metrics

To study the capacitive properties of the Pind electrode materials, cyclic voltammetry (CV) and galvanostatic charging-discharging (GCD) measurement techniques are commonly employed. With these techniques, one can quantify the amount of charge the electrodes can store and the charge-discharge cycles they can withstand during active use. The recorded electrochemical results from CV and GCD at a particular scan rate and the selected number of cycles are calculated from the equations below as

Summary and future directions

The article has systematically reviewed Pind CP with respect to its synthesis, characterization and application as active electrode material in batteries and supercapacitors. In comparison to Pani and PPy CPs, Pind is in an excellent position to compete well primarily in terms of capacitance, capacity and excellent retention across thousands of cycles when employed in these electrochemical energy devices. The Ragone plot of Pind and its composites is shown in Fig. 8, comparing them with

Declaration of Competing Interest

The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.

Acknowledgements

This work was funded by the National Natural Science Foundation of China (61705258). I. M is grateful the QUT PhD scholarship support. M.T acknowledges the research support from the Australian government research training program (AGRTP).

References (255)

  • Q.F. Meng et al.

    Research progress on conducting polymer based supercapacitor electrode materials

    Nano Energy

    (2017)
  • L. Lin et al.

    Two-dimensional transition metal dichalcogenides in supercapacitors and secondary batteries

    Energy Storage Mater.

    (2019)
  • D.-G. Wang et al.

    Metal-organic framework-based materials for hybrid supercapacitor application

    Coord. Chem. Rev.

    (2020)
  • M. Du et al.

    A review of electrochemical energy storage behaviors based on pristine metal–organic frameworks and their composites

    Coord. Chem. Rev.

    (2020)
  • M. Yuan et al.

    Redox polymers in electrochemical systems: from methods of mediation to energy storage

    Curr. Opin. Electrochem.

    (2019)
  • L.T. Yan et al.

    Biomass derived porous nitrogen doped carbon for electrochemical devices

    Green Energy Environ.

    (2017)
  • Y.Z. Jiang et al.

    Transition metal oxides for high performance sodium ion battery anodes

    Nano Energy

    (2014)
  • T. Xing et al.

    P-doped ternary transition metal oxide as electrode material of asymmetric supercapacitor

    J. Energy Storage

    (2020)
  • H.H. Wang et al.

    Polyaniline (PANi) based electrode materials for energy storage and conversion

    J. Sci.-Adv. Mater. Devices

    (2016)
  • P. Liu et al.

    Recent advancements of polyaniline-based nanocomposites for supercapacitors

    J. Power Sources

    (2019)
  • M. Tebyetekerwa et al.

    Unveiling polyindole: freestanding as-electrospun polyindole nanofibers and polyindole/carbon nanotubes composites as enhanced electrodes for flexible all-solid-state supercapacitors

    Electrochim. Acta

    (2017)
  • W.G. Wang et al.

    A new ternary composite based on carbon nanotubes/polyindole/graphene with preeminent electrocapacitive performance for supercapacitors

    Appl. Surf. Sci.

    (2017)
  • Z.J. Cai et al.

    Synthesis of polyindole and its evaluation for Li-ion battery applications

    Synth. Met.

    (2010)
  • M. Tebyetekerwa et al.

    Green approach to fabricate Polyindole composite nanofibers for energy and sensor applications

    Mater. Lett.

    (2017)
  • A.K. Thakur et al.

    Enhanced electrochemical performance of polypyrrole coated MoS2 nanocomposites as electrode material for supercapacitor application

    J. Electroanal. Chem.

    (2016)
  • A. Eftekhari et al.

    Polyaniline supercapacitors

    J. Power Sources

    (2017)
  • J.G. Mackintosh et al.

    The electropolymerization and characterization of 5-Cyanoindole

    J. Electroanal. Chem.

    (1995)
  • E.B. Maarouf et al.

    Electrochemical cycling and electrochromic properties of polyindole

    Mater. Res. Bull.

    (1994)
  • J. Li et al.

    Polyindole vertical nanowire array based electrochromic-supercapacitor difunctional device for energy storage and utilization

    Eur. Polym. J.

    (2019)
  • D. Billaud et al.

    Chemical oxidation and polymerization of indole

    Synth. Met.

    (1995)
  • W.Q. Zhou et al.

    High efficient electrocatalytic oxidation of formic acid on Pt/polyindoles composite catalysts

    Electrochim. Acta

    (2010)
  • S. Palaniappan et al.

    Facile synthesis of bis(indolyl)methanes using polyindole salt as reusable catalyst

    J. Mol. Catal. A: Chem.

    (2005)
  • C. Zhijiang et al.

    Electrochemical properties of electrospun polyindole nanofibers as a polymer electrode for lithium ion secondary battery

    J. Power Sources

    (2013)
  • T. Tuken et al.

    The use of polyindole for mild steel protection

    Prog. Org. Coat.

    (2004)
  • Q.J. Zhou et al.

    PEDOT:PSS-assisted polyindole hollow nanospheres modified carbon cloth as high performance electrochemical capacitor electrodes

    Electrochim. Acta

    (2016)
  • H. Shirakawa et al.

    Synthesis of electrically conducting organic polymers - halogen derivatives of polyacetylene, (Ch)X

    J. Chem. Soc., Chem. Commun.

    (1977)
  • The Nobel Prize in Chemistry 2000,...
  • Y. Shi et al.

    Nanostructured conductive polymers for advanced energy storage

    Chem. Soc. Rev.

    (2015)
  • F. Vilela et al.

    Conjugated porous polymers for energy applications

    Energy Environ. Sci.

    (2012)
  • A.M. Bryan et al.

    Conducting polymers for pseudocapacitive energy storage

    Chem. Mater.

    (2016)
  • A. Lendlein et al.

    Polymers in biomedicine and electronics

    Macromol. Rapid Commun.

    (2010)
  • J. Janata et al.

    Conducting polymers in electronic chemical sensors

    Nat. Mater.

    (2003)
  • H. Bai et al.

    Gas sensors based on conducting polymers

    Sensors

    (2007)
  • P.P. Deshpande et al.

    Corrosion Protection of Metals By Intrinsically Conducting Polymers

    (2016)
  • G.M. Spinks et al.

    Electroactive conducting polymers for corrosion control

    J. Solid State Electrochem.

    (2002)
  • P.P. Deshpande et al.

    Conducting polymers for corrosion protection: a review

    J. Coat. Technol. Res.

    (2014)
  • S.P. Sitaram et al.

    Application of conducting polymers in corrosion protection

    J. Coat. Technol.

    (1997)
  • R. Ansari

    Polypyrrole conducting electroactive polymers: synthesis and stability studies

    J. Chem.

    (2006)
  • C.O. Baker et al.

    Polyaniline nanofibers: broadening applications for conducting polymers

    Chem. Soc. Rev.

    (2017)
  • J. Stejskal et al.

    Polyaniline. preparation of a conducting polymer (IUPAC technical report)

    Pure Appl. Chem.

    (2002)
  • Cited by (61)

    View all citing articles on Scopus
    View full text