Strong and Stretchable Polypyrrole Hydrogels with Biphase Microstructure as Electrodes for Substrate‐Free Stretchable Supercapacitors

Abstract

materials and stretchable substrates. [15] But these substrates are generally electrochemically nonactive elastomers, which would occupy a significant volume and mass in SSCs, and reduce specific capacitance and energy density of SSCs. In addition, due to the mismatch of Young's modulus of soft substrates and rigid electroactive materials, inevitable dislocation occurs at the interface upon a large deformation, which could damage the integrity and hence the electrochemical performance of SSCs. [16] On the other hand, specific structures can extend flexibility to stretchability. For instance, wavy structure [12][13][14] resembling spongy structure, also called winkled [17,18] or buckled structure, [19,20] can be used for rigid materials to achieve a certain level of stretchability, such as single-crystal Si, [21] graphene film, [17,19] and interwoven carbon nanotube. [18,20] Multistep processing is typically required to obtain these wavy structures, such as exploiting and removing buckled templates, [17] prestraining, and releasing elastic substrates. [18] Some fiber-shaped electroactive materials can be woven into overtwisted yarn [22][23][24][25] to achieve a certain level of stretchability. Besides these strategies, there are rarely any reports of stretchable supercapacitors without using elastic substrates or complicate fabrication, like wavy or yarn structures.Carbon-based materials [26,27] are often chosen as the electroactive materials of SSCs, while the specific capacitance of obtained SSC devices is limited by the low theoretical capacitance of carbon-based materials. In contrast, conducting polymers show a much higher specific capacitance, and are often composite with carbon materials to achieve enhanced capacitance. [22,[28][29][30] Recently, conductive polymer-based hydrogels (CPHs) have been developed for flexible supercapacitors, and these CPH-based flexible supercapacitors show enhanced specific capacitance and cycling stability. [31][32][33][34] However, the conductivity of most of current CPHs is typically in the range of 10 −4 -10 −1 S cm −1 , [35,36] which is not sufficient, and conductive supports are required as current collector to assemble electrodes. Since these conductive supports such as carbon cloth or metal mesh are not stretchable, the obtained CPH-based flexible supercapacitors are not stretchable. To bypass the usage of conductive supports, the development The development of stretchable supercapacitors (SSCs) is heading to compact and robust devices with higher capacitance and simpler preparation process. Herein, a new strategy is reported to prepare a highly stretchable and conductive polypyrrole hydrogel with a unique biphase microstructure (loose phase and dense phase), which is formed by the supramolecular assembly of polypyrrole (PPy), poly(vinyl alcohol), and anionic micelles. The loose phase enables the PPy hydrogel large stretchability (elongation at a break of 500%) and good electrochemical capacitive behavior, while the dense phase enables the PPy hydrogel high tensile stre...

Hierarchically Structured Stretchable Conductive Hydrogels for High-Performance Wearable Strain Sensors and Supercapacitors

“…In an attempt to improve the stretchability, elastic polymer chains such as polyvinyl alcohol (PVA), [19][20][21] polyacrylamide (PAAm), 22,23 poly(ethylene glycol)diacrylate, 4 and chitosan 24 have been incorporated into rigid conducting polymers in past works. However, these strategies usually suffer from unfavorable electrical and mechanical properties.…”

Wood‐Inspired Morphologically Tunable Aligned Hydrogel for High‐Performance Flexible All‐Solid‐State Supercapacitors

“…The cyclic voltammetry (CV) curves of devices made from PPy/APA matrices with different pore sizes (APA‐ x PVA, x = 0, 0.5, 3 wt% PVA) and nonaligned, homogenous matrix (HomoPA), respectively, were measured at 10 mV s −1 . As shown in Figure b, all four CV curves demonstrated a nearly rectangular shape, indicating a fast and efficient ion transfer . The enclosed CV area for the APA devices increased with decreasing pore size, an indication of higher loading of electrode materials.…”

“…Based on the 2 mm APA/PPy electrode with 3 wt% PVA and 28% FeCl 3 /ethanol solution, the resultant areal capacitance was boosted to 1838 mF cm −2 at 6.2 mA cm −2 , shown in Figure S10 in the Supporting Information. To the best of our knowledge, this capacitance is among the highest of hydrogel‐based solid‐state supercapacitors . Therefore, this presents a promising strategy that the morphological designs of anisotropic matrices and electrode materials coating can possibly advance energy storage devices and technologies.…”

“…b) GCD curves at various current densities from 6.2 to 15.5 mA cm −2 . c) Ragone plots comparing this supercapacitor with other representative flexible all‐solid‐state supercapacitors, including PPy/PVA, sodium dodecyl sulfate‐modified PPy/PVA, all‐in‐one PANi/PVA, all‐in‐one PPy/PVA, PPy/GO (graphene oxide), graphite/PANi, carbon nanotube/GO/PPy, graphene/PANi, and PANi/stainless steel wire . d) Capacitance retention during 1000 charging–discharging cycles at current density of 6.2 mA cm −2 .…”

Electroconductive hydrogels for biomedical applications

“…Electroconductive hydrogels (EHs) obtained by introducing conductive components into conventional hydrogels have been widely reported and studied since they were firstly reported in 1994 (Gilmore, Hodgson, Luan, Small, & Wallace, ). Conductive polymers such as polypyrrole (F. Chen, Chen, Song, Lu, & Ma, ; Hur et al, ; L. Li et al, ), polyaniline (W. Li, Gao, Wang, Zhang, & Ma, ; Pan et al, ), polythiophene and derivatives (Q. Chen et al, ; Q. Chen, Wang, Chen, Zhang, & Ma, ; Ghosh, Rasmusson, & Inganäs, ; Yao et al, ) and conductive carbon materials such as carbon nanotubes (CNTs; Z. Chen et al, ), graphene (Xu, Sheng, Li, & Shi, ) are commonly used for synthesizing EHs (F. Zhao, Bae, Zhou, Guo, & Yu, ; F. Zhao, Shi, Pan, & Yu, ). The π–π‐conjugated structure of conductive components provide the hydrogels with good electrical conductivity (Zhang et al, ).…”