Highly conductive paper was fabricated through polypyrrole (PPy) coating on common printing paper by a simple and low-cost “soak and polymerization” method. The as-fabricated porous, flexible and conductive paper shows a high electrical conductivity of 15 S cm−1 and a low sheet resistance of 4.5 Ω sq−1. Flexible solid-state supercapacitors assembled with PPy/paper composite electrodes had an average weight of 55 mg and an areal capacitance of 0.42 F cm−2, indicating a high energy density of 1 mW h cm−3 at a power density of 0.27 W cm−3 normalized to the volume of the whole cell (electrode, electrolyte, and separator). Furthermore, this method could be easily scaled up to large-scale fabrication of conductive paper and opened up new opportunities for flexible energy storage.

Polypyrrole-coated paper for flexible solid-state energy storage

Paper-based supercapacitors (SCs), a novel and interesting group of flexible energy storage devices, are attracting more and more attention from both industry and academia. Cellulose papers with a unique porous bulk structure and rough and absorptive surface properties enable the construction of paper-based SCs with a reasonably good performance at a low price. The inexpensive and environmentally friendly nature of paper as well as simple fabrication techniques make paper-based SCs promising candidates for the future ‘green’ and ‘once-use-and-throw-away’ electronics. This review introduces the design, fabrication and applications of paper-based SCs, giving a comprehensive coverage of this interesting field. Challenges and future perspectives are also discussed.

Flexible supercapacitors based on paper substrates: a new paradigm for low-cost energy storage.

A solid-state flexible supercapacitor (SC) based on organic-inorganic composite structure was fabricated through an “in situ growth for conductive wrapping” and an electrode material of polypyrrole (PPy)-MnO2 nanoflakes-carbon fiber (CF) hybrid structure was obtained. The conductive organic material of PPy greatly improved the electrochemical performance of the device. With a high specific capacitance of 69.3 F cm−3 at a discharge current density of 0.1 A cm−3 and an energy density of 6.16 × 10−3 Wh cm−3 at a power density of 0.04 W cm−3, the device can drive a commercial liquid crystal display (LCD) after being charged. The organic-inorganic composite active materials have enormous potential in energy management and the “in situ growth for conductive wrapping” method might be generalized to open up new strategies for designing next-generation energy storage devices.

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Solid-state high performance flexible supercapacitors based on polypyrrole-MnO2-carbon fiber hybrid structure.

Freestanding bacterial cellulose–polypyrrole nanofibres paper electrodes for advanced energy storage devices

A very simple, environmentally friendly, one-step oxidative polymerization route to fabricate polypyrrole (Ppy) nanoparticles of fixed size and morphology was developed and investigated. The herein proposed method is based on the application of sodium dodecyl sulfate and hydrogen peroxide, both easily degradable and cheap materials. The polymerization reaction is performed on 24 h time scale under standard conditions. We monitored a polaronic peak at 465 nm and estimated nanoparticle concentration during various stages of the reaction. Using this data we proposed a mechanism for Ppy nanoparticle formation in accordance with earlier emulsion polymerization mechanisms. Rates of various steps in the polymerization mechanism were accounted for and the resulting particles identified using atomic force microscopy. Application of Ppy nanoparticles prepared by the route presented here seems very promising for biomedical applications where biocompatibility is paramount. In addition, this kind of synthesis could be suitable for the development of solar cells, where very pure and low-cost conducting polymers are required.

Polymerization Model for Hydrogen Peroxide Initiated Synthesis of Polypyrrole Nanoparticles

A novel strategy for the one-pot fabrication of free-standing polypyrrole films is presented in this work. The films are spontaneously formed at an air/ionic liquid interface through interface oxypolymerization. The thicknesses of the films are finely controlled from tens to hundreds of nanometers, and the films are uniform and compact. Asymmetrical films with different smoothness on the two sides of the film are also obtained and exhibit different water wettability. This method is extremely simple and does not need any equipment. It may bring about a general methodology for forming free-standing conducting polymer films.

Spontaneous growth of free-standing polypyrrole films at an air/ionic liquid interface.

Novel gel-like poly(ethylene dioxythiophene) (PEDOT) microspheres were fabricated via micelle-mediated polymerization from room temperature ionic liquids (RTILs). The microspheres consist of PEDOT chains as three-dimensional solid networks and a large volume of EDOT as liquid medium span them. Due to synergistic effect of micelles and RTILs, the polymerization rate of PEDOT in the system is slowed down greatly. Gel-like PEDOT microspheres spontaneously grew from several tens of nanometers to centimeter scale and the whole process lasted for several days. Thus, the growth of the microspheres is tracked in situ. The microspheres could release and adsorb EDOT reversibly under certain conditions, indicating a gel-like behavior.

Yan-Xiang Li

Papers

Spontaneous growth of free-standing polypyrrole films at an air/ionic liquid interface.

Micelle-assisted fabrication of gel-like PEDOT microspheres: in situ observation of the growth process