Fabrication of Graphene/Poly(styrenesulfonic acid-g-aniline) Composites for High Performance Supercapacitor Electrodes

Abstract

Polyaniline (PANI) as a potential candidate for supercapacitor electrode has high theoretical specific capacitance of about 2000 F/g. However, PANI itself suffers from poor solubility in common solvents, which restricts fabrication of supercapacitor electrodes directly from PANI. In our previous report, we synthesized a water-soluble and self-doped conducting polymer, poly(styrenesulfonic acid)-graft-polyaniline (PSSA-g-PANI), to overcome the solubility problem of PANI. When PSSA-g-PANI is added into graphite in ethanol, it is realized that the graft copolymer exfoliates graphite into graphene layers to form in-situ composite of graphene/PSSA-g-PANI, because PANI in PSSA-g-PANI is strongly physisorbed onto graphene surface via strong  interaction while PSSA in PSSA-g-PANI enhances the solubility in ethanol. To the best of our knowledge, this is the only PANI/graphene composite fabricated by direct exfoliation method. Compared to other fabrication methods for PANI/graphene composites such as in-situ polymerization and electrodeposition, the direct exfoliation method provides high quality of graphene layers without degrading the sp2 structure because graphite is directly used as a precursor without chemical treatment, and also minimizes the fabrication step by simply mixing graphite and the polymer. As a consequence, PSSA-g-PANI/graphene composite is easily fabricated by a solution process and used directly for supercapacitor electrodes.When the capacitance of the composite was measured by the Galvanostatic method, the composite exhibits high specific capacitance of 767 F/g at 0.5 A/g, which is among the highest value of supercapacitor electrodes based on PANI/graphene composites. This high value is attributed to high specific area of graphene and high pseudo-capacitance of PANI. Furthermore, PSSA-g-PANI/graphene composite retains 82% of its initial capacitance after 1000 cycles, indicating that the composite has high electrochemical stability.