Yi Zhao, Jinzhang Liu*
School of Materials Science and Engineering, Beihang University, Beijing 100191, China
Nano-Micro Conference, 2017, 1, 01075
Published Online: 16 November 2017 (Abstract)
A novel approach for increasing the specific capacitance of graphene-based supercapacitors is reported. In this work, Kapton, which is polyimide (PI) film widely used in industry, is used as the starting material to functionalize graphene. Hydrolysis of PI in alkalic solution released small aromatic molecules containing pyrrolic nitrogen that can be dissolved in water and easily adsorbed onto graphene sheets via π-π interaction (Figure 1). These small molecules store charge via a redox process, endowing graphene with pseudocapacitance and increasing the specific capacitance. N-doped graphene films are obtained by hydrothermally reducing solid composite films consisting of graphene oxide, ammonium acetate, and salt. These films are firstly used as electrodes to make symmetric supercapacitors with H2SO4 aqueous electrolyte as electrolyte, and show specific capacitances around 310 F/g. After the adsorption of hydrolysized PI molecules, the weight of graphene film is ~3% increased, and the specific capacitance was remarkable increased up to 467 F/g. Notably, the areal specific capacitance is in the scale of 1.2 F/cm2. When using the Li2SO4 aqueous electrolyte that can extend the potential window to 1.5 V, the device also remains high specific capacitance around 445 F/g, and exhibits high energy densities up to 35 Wh/Kg. Our devices not only deliver excellent capacitive performances in aqueous electrolyte (89% capacitance retention at 20 A/g and 85% capacitance retention over 5 000 cycles), but also exhibit extraordinary mechanical flexibility. This novel strategy by adsorbing small molecules from hydrolysized PI provides a promising route towards high-performance supercapacitors.
Figure 1. Illustration of the adsorption of hydrolysized PI molecules onto graphene sheet.
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