Boosting the Energy Density of Flexible Supercapacitors by Redox-Additive Hydrogels

Abstract

Flexible energy storage devices are the cornerstone to the development of future-generation electronics such as flexible displays on phones, smart bands, laptops, and televisions. The advancement of flexible supercapacitors has turned into an essential task because supercapacitors are designed with the rewards of optimum power and energy density. Owing to the dual function as an electrical double-layer capacitor and a pseudocapacitor, heteroatom-doped graphene is presumed to be a promising electrode material for supercapacitor applications. Herein, we report p-toluenesulfonic acid as the precursor to the formation of sulfur-doped graphene by supercritical fluid-aided processing. Both the existence and nature of S doping in graphene were confirmed with the elemental and X-ray photoelectron spectroscopy techniques. Full cell analysis indicated that the energy density achieved using hydroquinone (HQ) as a redox additive in 1 M H2SO4 solution was found to be 27 W h/kg, which is twice that of an aqueous solution of 1 M H2SO4 (13 W h/kg). To extend the application of the symmetric cell, a flexible device using polyvinyl alcohol (PVA)/HQ/H2SO4 is fabricated. A 3-fold increase in energy density is observed for the flexible solid-state single device using PVA/HQ/H2SO4 (E = 21.3 W h/kg) when compared with PVA/H2SO4 as an electrolyte (E = 7.7 W h/kg).

Flexible and Wearable Zinc-Ion Hybrid Supercapacitor Based on Double-Crosslinked Hydrogel for Self-Powered Sensor Application

“…At a current density of 1.0 mA cm −2 , the discharge capacitance of the ZHS device is as high as 1.364 F cm −2 , while the capacitance remained at 1.244 F cm −2 when the current density was further increased to 2.0 mA cm −2 . The calculated energy density for the ZHS device was 242 Wh kg −1 at a power density of 228 W kg −1 , i.e., superior to those of other sandwich-structure supercapacitors ( Figure 3 d) [ 25 , 26 , 33 , 34 , 35 , 36 , 37 , 38 , 39 ]. The cyclic stability test of the ZHS ( Figure S6 ) showed 90% retention after 1000 cycles, indicating stable charge–discharge performance.…”

“…( d ) Comparison of energy density and power density among reported cutting-edge supercapacitors. (Yang, 2020 [ 25 ]; Liu, 2021 [ 26 ]; Chen, 2019 [ 33 ]; Zhang, 2021 [ 34 ]; Ding, 2021 [ 35 ]; Sandhiya, 2020 [ 36 ]; Khazaeli, 2020 [ 37 ]; Li, 2020 [ 38 ]; Sun, 2018 [ 39 ]) ( e ) Ragone plots of the ZHSs with the hydrogel prepared with different Zn 2+ concentrations. ( f ) Discharge capacitance of ZHS at different temperatures.…”

Fabrication of Flexible Supercapacitor Using N-Doped Porous Activated Carbon Derived from Poultry Waste

“…The functioning of such devices has to be improved to comply with the requirements of future systems. , The supercapacitors are categorized into three types based on the materials used and charge-storage mechanism: (i) electrical double-layer capacitors (EDLC), (ii) pseudocapacitors, and (iii) hybrid capacitors. , The EDLC uses carbon-based active material for simple adsorption–desorption of electrolytes ion on the electrode–electrolyte interface and confer the possibility as a good conductor with the increased specific surface area. − The pseudocapacitor works by fast and reversible surface and near-surface reactions. , The hybrid capacitor utilizes the advantages of both EDLC and pseudocapacitor electrodes. − The carbon-based EDLC materials has been used as commercial supercapacitor electrodes due to its cost-effectiveness and natural abundance. The most investigated carbon-based materials include activated carbon, carbon nanotubes, carbon nanofibers, graphene, carbon aerogel, carbide-derived carbon, and nanosized carbon. In addition, biowaste-derived activated carbon are in consideration for preparing electrode materials for supercapacitor performance, which is attributable to advantages such as wide availability, hassle-free preparation, and evading the problem of waste disposal.…”

Graphene based sulfonated polyvinyl alcohol hydrogel nanocomposite for flexible supercapacitors

“…In recent years, there has been sharp increase in the development of flexible supercapacitors (FSCs) for electronic devices as power sources, which have to be ultra-thin and flexible in-order to serve their purpose [1][2][3][4]. FSCs with high specific energy, specific power and excellent cycle life are much desirable to supply the rising market of flexible and wearable electronic devices in the near future [5,6].…”

“…Incorporation of nanofillers and redox-active materials into GPEs leads to rise in amorphous nature thereby improving ion conductivity [30,31]. Recently, redox-additives like Na 2 MoO 4 [5], hydroquinone [32], alizarin red [33] and indigo carmine [34] have been incorporated into PVA-H 2 SO 4 for application in supercapacitors.…”