Elsevier

Electrochimica Acta

Volume 305, 10 May 2019, Pages 187-196
Electrochimica Acta

A textile-based wearable supercapacitor using reduced graphene oxide/polypyrrole composite

https://doi.org/10.1016/j.electacta.2019.03.058Get rights and content

Abstract

Wearable electronics such as supercapacitors have been extensively explored and developed. Textile-based composites hold excellent promise as suitable hosts for electronic devices for the development of smart garments. In the present work, a textile-based electrode is developed through modification with reduced graphene oxide (rGO) nanosheets and polypyrrole (PPy) nanospherical particles onto polyethylene terephthalate (PET) fabric. The conductive composites are used to fabricate flexible, all-solid-state supercapacitors by using a gel electrolyte. The optimum device delivers an areal capacitance of 0.23 F cm−2 at a scanning rate of 1 mV s−1, a volumetric capacitance of 5.5 F cm−3 at a discharge current density 1.6 mA cm−3, an energy density of 11 μWh cm−2 and a power density of 0.03 mW cm−2 corresponding to 6.86 mg cm−2 of electroactive materials loading. It also retains about 76% of the initial capacitance after 6000 cyclic voltammetric cycles and possesses excellent stability under bending.

Introduction

Textile-based energy storage devices have gained great attention for applications in wearable electronics, due to the excellent mechanical flexibility, breathability and feeling of comfort, that enable them to be successfully integrated within various smart garments [[1], [2], [3], [4]].

Supercapacitors provide charge storage based either on the charge accumulation from an electrolytic solution through electrostatic attraction by polarized electrodes and/or pseudocapacitance generated by redox-active species [5]. They have advantages over batteries since they generally deliver higher power density, longer cycle life and faster charge-discharge operation. However, supercapacitors mainly suffer from low energy density [6].

Textiles as a 3D porous body for electrode fabrication lead to a good flexibility, providing ample space for loading of electrochemically active materials and facilitating fast ion movements inside the electrodes [7,8]. The electrochemically active materials typically loaded into textile are carbonaceous materials [7,[9], [10], [11]], metal oxides [[12], [13], [14]], metal hydroxides [15], conducting polymers (CPs) such as polypyrrole (PPy) [16,17] and their composites [18,19]. Composites of carbon materials and conducting polymers benefit from the unique advantages of each component. Generally, carbonaceous materials present high surface area, large electrical double layer capacitance (EDLC), a stable framework hindering CP swelling, consequently improving cycleability. On the contrary, introducing CPs to the composite enhances the conductivity, capacitance and energy density [20]. Various procedures have been reported for preparing rGO/PPy composites with diverse morphologies aiming to enhance electrical and electrochemical features. It has been proved that the morphology of PPy in the composite affects drastically the electrochemical performance. PPy has been synthesized in the form of nanoparticles, nanosheets, porous hydrogels and mainly nanowires or nanotubes [[21], [22], [23], [24], [25]]. The different structures of PPy result in diverse macroscopic configurations, subsequently in varied electrochemical performance [24,26]. Pattananuwat and Aht-ong reported a method to achieve controllable morphology of a graphene hydrogel/PPy nanocomposite by using different surfactants. They demonstrated that the micro/nanostructure of PPy wrapped graphene enhancing at the same time the capacitive behavior through shortening of the diffusion paths of the electrolyte ions. A specific capacitance of 640 F g−1 at 1 A g−1 and almost negligible IR drop were obtained in this case [26].

Xu et al. fabricated PPy/reduced graphene oxide (rGO) coated cotton fabric reporting the capacitance of 336 F g−1 at a current density of 0.6 mA cm−2 while only 1.5 mg cm−2 of electrochemical active material was loaded on the cotton. A capacitance retention of 64% was achieved over 500 charge-discharge cycles [18]. Recently, Liang et al. reported an asymmetric supercapacitor by CNT/rGO and PPy coated cotton electrodes with mass loading of 7.7 and 5.7 mg cm−2, respectively. A maximum capacitance of 570 mF cm−2 at 1 mA cm−2 and 9% loss in capacitance after 1000 cycles were achieved [27].

Polyethylene terephthalate (PET) fabric, well-known in apparel industry and daily-used clothing was chosen as flexible substrate owing to the hierarchical porosity, stability against strong acid and low cost. Reduced graphene oxide as a reliable candidate of carbon family was used according to the noteworthy specific surface area and conductivity [28]. PPy was representative of CPs because of high conductivity, stability in the oxidized state and ease during the synthesis process [20]. To the best of our knowledge, such a composite and the fabricated supercapacitor device have not been reported to date.

A serious challenge dealing with producing textile-based electrodes is related to compromising between loading mass, conductivity, preservation of general textile properties and electrochemical performance. Too thick coating may lead to better conductivity but deteriorates the capacitive behavior due to blockage of electrolyte ion movement, as well as longer diffusion paths [1,21]. Multi-cycle dip coating was employed as a simple method to investigate the effect of loading mass and thickness on the conductivity and the capacitive performance of PET fabric coated electrodes.

In the present work, an electrically and electrochemically active PET fabric has been developed through the facile dipping and drying approach. After chemical reduction of GO and subsequently chemical growth of PPy on the PET, two ternary composites of PET/rGO-x/PPy were prepared, where x equals to 1 and 5 mg ml−1 according to GO concentration. The free-standing symmetrical sandwich-type supercapacitors of each composite were fabricated using gel electrolyte. The morphological, chemical, electrical and electrochemical performances of the devices were assessed.

Section snippets

Materials and reagents

All reagents used were of analytical grade. Graphite flakes (<20 μm), sulphuric acid (H2SO4), sodium nitrate (NaNO3, 99%), potassium persulfate (K2S2O8, 99%), phosphorus pentoxide (P2O5, 99%), hydrochloric acid (HCl, 37%), hydrogen peroxide (H2O2, 35%), pyrrole (C4H4NH, 99%), polyvinyl alcohol (PVA, Mw = 89,000–98,000, 99% hydrolyzed) and ferric chloride (FeCl3, 98%) were purchased from Sigma-Aldrich Company. Potassium permanganate (KMnO4, 99%) was supplied by ACS Merck Co. Polyethylene

Results and discussion

The synthesis and fabrication procedure is briefly illustrated in Fig. 1. Table 1 describes the fabric properties before and after loading of the active materials. The GO uptake onto the fabric matrix increases as the GO concentration was increased to 5 from 1 mg ml−1. Taking into account that the same Py concentration was used for both composites, it is evident that the amount of loaded PPy is higher in the case of PET/rGO-5/PPy. The amount of loaded PPy can be calculated by the subtraction of

Conclusions

Composites of PET/GO-x (x = 1 and 5) were prepared by using a facile dipping and drying method. A green reduction approach using vitamin C was employed to obtain PET/rGO-x. XRD patterns and Raman spectra proved the partial reduction of GO to rGO. Afterwards, PPy nanospherical particles were grown on the surface of PET/rGO-x composites through an oxidation polymerization method. FTIR analysis and Raman spectroscopy results confirmed the PPy formation on the surface of the composites.

Funding

This research did not receive any specific grant from funding agencies in the public, commercial, or not-for-profit sectors.

Acknowledgment

We thank Oddvar Dyrlie and Drs. Ragnar Strandbakke and Amir Masoud Dayaghi, University of Oslo, for their valuable assistance and advice.

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