Facile synthesis and electrochemical capacitance of composites of polypyrrole/multi-walled carbon nanotubes

Toward fiber-, paper-, and foam-based flexible solid-state supercapacitors: electrode materials and device designs

Flexible solid-state supercapacitors possess promising safety performance and intrinsic fast charging-discharging properties, enabling them to accomplish the requirements of lightweight and multifunctional wearable electronics that have recently become fairly popular. Because electrode materials are the core component of flexible solid-state supercapacitors, we exhaustively review the recent investigations involving electrode materials that have used carbons, metal oxides, and conductive polymers. The principles and methods of optimizing and fabricating electrodes for use in flexible supercapacitors are discussed through a comprehensive analysis of the literature. In addition, we focused on three types of flexible solid-state supercapacitors (fiber-, paper-, and porous foam-based structures) to satisfy the requirements of flexible electronic devices. Further, we summarize the practical applications of flexible solid-state supercapacitors, including energy conversion/collection devices and energy storage/detection devices. Finally, we provide the developmental direction for flexible solid-state supercapacitors in the future.

A stretchable and bendable all-solid-state pseudocapacitor with dodecylbenzenesulfonate-doped polypyrrole-coated vertically aligned carbon nanotubes partially embedded in PDMS

We present an all-solid-state flexible and stretchable pseudocapacitor composed of dodecylbenzenesulfonate-doped polypyrrole (PPy(DBS))-coated vertically aligned carbon nanotubes (VACNTs) partially embedded in a polydimethylsiloxane (PDMS) substrate. VACNTs are grown via atmospheric-pressure chemical vapor deposition on a Si/SiO₂ substrate and transferred onto PDMS. Then, the PPy(DBS) film is coated with a surface charge of 300 mC cm^-2 on individual carbon nanotubes (CNTs) via electropolymerization. The partial embedment of VACNTs in PDMS permits a rapid and facile integration of the PPy(DBS)/CNTs/PDMS structure to construct a flexible and stretchable supercapacitor electrode. The measured capacitance is 3.6 mF cm^-2 with a PVA-KOH gel electrolyte at a scan rate of 100 mV s^-1, which is maintained under stretching from 0% to 150% and bending/twisting angles from 0° to 180°. This all-solid-state stretchable supercapacitor shows a stable galvanostatic performance during 10 000 charge/discharge cycles with its capacitance retained at 109%.

Specific Surface versus Electrochemically Active Area of the Carbon/Polypyrrole Capacitor: Correlation of Ion Dynamics Studied by an Electrochemical Quartz Crystal Microbalance with BET Surface

Carbon/polypyrrole (PPy) composites are promising electrode materials for energy storage applications such as lightweight capacitors. Although these materials are composed of relatively inexpensive components, there is a gap of knowledge regarding the correlation between surface, porosity, ion exchange dynamics, and the interplay of the double layer capacitance and pseudocapacitance. In this work we evaluate the specific surface area analyzed by the BET method and the area accessible for ions using electrochemical quartz-crystal microbalance (EQCM) for SWCNT/PPy and carbon black Vulcan XC72-R/PPy composites. The study revealed that the polymer has significant influence on the pore size of the composites. Although the BET surface is low for the polypyrrole, the electrode mass change and thus the electrochemical area are large for the polymer-containing electrodes. This indicates that multiple redox active centers in the charged polymer chain are good ion scavengers. Also, for the composite electrodes, the effective charge storage occurs at the polypyrrole-carbon junctions, which are easy to design/multiply by a proper carbon-to-polymer weight ratio. The specific BET surface and electrochemically accessible surface area are both important parameters in calculation of the electrode capacitance. SWCNTs/PPy showed the highest capacitances normalized to the BET and electrochemical surface as compared to the polymer-carbon black. TEM imaging revealed very homogeneous distribution of the nanosized polymer particles onto the CNTs, which facilitates the synergistic effect of the double layer capacitance (CNTs) and pseudocapacitance (polymer). The trend in the electrode mass change in correlation with the capacitance suggest additional effects such as a solvent co-insertion into the polymer and the contribution of the charge associated with the redox activity of oxygen-containing functional groups on the carbon surface.

Electrochemical preparation and characterization of a polypyrrole/nickel-cobalt hexacyanoferrate nanocomposite for supercapacitor applications

A new electrode material for supercapacitor application is introduced based on polypyrrole conductive polymer and nickel-cobalt hexacyanoferrate poly-nuclear inorganic compound.