Sandwich nanocomposites of polyaniline embedded between graphene layers and multi-walled carbon nanotubes for cycle-stable electrode materials of organic supercapacitors

Abstract

Intrinsically conducting polymers like polyaniline (PANI) demonstrate much higher specific capacitance than carbon based materials for the electrode active materials of supercapacitors, but the cycle-stability of PANI is rather poor. The reason may lie in the internal stress change of PANI due to the counter-anions intercalating/dissociating during doping and dedoping. Here we proposed a sandwich nanocomposite methodology where electroactive PANI was sandwiched between a conducting graphene layer and a multi-walled carbon nanotubes (MWCNTs) layer, i.e., PANI was first deposited on the surface of MWCNTs nanofibers via in situ copolymerization of aniline and p-phenylenediamine in the acidic dispersion of MWCNTs to fabricate the one-dimensional PANI/MWCNTs nanofibers, then the assembly between graphene oxide sheets and PANI/MWCNTs nanofibers was realized by electrostatic interactions, followed by a reduction of the graphene oxide to obtain the sandwich nanocomposites. The hybrids demonstrated superior electrochemical properties in comparison with the pristine PANI in a propylene carbonate/1M Et₄N⁺·BF₄⁻ electrolyte. The specific capacitance of the hybrid composites was 259.4 F g⁻¹ at the current density of 0.5 A g⁻¹, and over 76.5% of the initial specific capacitance was retained over 2500 charging/discharging cycles, much better than that for pure PANI (only 38.9% retention).