Abstract
Three-dimensional (3D) graphene-based hydrogels have attracted great interest for applying in supercapcacitors electrodes, owing to their intriguing properties that combine the structural interconnectivities and the outstanding properties of graphene. However, the pristine graphene hydrogel can not satisfy the high-performance demands, especial in high specific capacitance. Consequently, novel graphene-based composite hydrogels with increased electrochemical properties have been developed. In this mini review, a brief summary of recent progress in the research of the three-dimensional graphene-based composite hydrogel for flexible supercapacitors electrodes materials is presented. The latest progress in the graphene-based composite hydrogel consisting of graphene/metal, graphene/polymer, and atoms doped graphene is discussed. Furthermore, future perspectives and challenges in graphene-based composite hydrogel for supercapacitor electrodes are also expressed.
Highlights
In recent years, supercapacitors have been attracted intensive investigation for sustainable energy application, because of their advantages in excellent power density and high charge/discharge rates (Li et al, 2018)
Previous studies have demonstrated that the supercapacitors based on graphene can possess excellent specific capacitance (Horn et al, 2019)
The restacking or irreversible agglomeration of graphene sheets can suppress the high conductivity and decrease accessible surface area, which limit the improvement of capacitive performance
Summary
Supercapacitors have been attracted intensive investigation for sustainable energy application, because of their advantages in excellent power density and high charge/discharge rates (Li et al, 2018). Functional materials or dopants such as metal oxides or hydroxide, conducting polymers, and so on have been introduced to the graphene hydrogels to further improve the electrochemical performance In this mini-review, a brief retrospect on graphene-based composite hydrogel materials for flexible supercapacitor electrodes will be provided. Zou et al (2018b) used m-phenylenediamine (mPD) to preserve the conjugated structure of PANI, and the composite hydrogel showed an improved capacity of 514.3 F/g They developed doublecrosslinked network functionalized graphene/PANI hydrogel with high specific capacitance and mechanical strength (Zou et al, 2018a). Li et al (2017a) reported lignosulfonate functionalized graphene hydrogels, which can present a specific capacitance of 432 F/g These renewable composite hydrogels exhibit great potential in supercapacitor as electrodes materials. After co-doping, the pseudo capacitance of the graphene will be increase, because of the redox faradic reactions existed at nitrogen-containing groups and sulf-containing species. Tran et al (2016) outlined that N and S co-doped graphene hydrogel with holy defect can show a wonderful specific capacitance of 538 F/g at 0.5 mV/s, and the electrochemical property of the hydrogel can be modulated by the level of N and S doping. Li et al (2017b) synthesized N/S co-doped graphene hydrogels with hierarchical pores, which can demonstrate a very good specific capacitance (251 F/g at 0.5 A/g) surprisingly. Zhang et al (2018a) developed a one-step method to synthesize N/S co-doped graphene hydrogel, and the as-prepared hydrogel can show a capacity of 1,063 C/g at 1 A/g. Kong et al (2018) constructed N,S-codoped graphene hydrogel with 3D hole, and the abundant in-plane pores leading to an outstanding specific capacitance of 320.0 F/g at 1 A/g
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