Chemically grafted p-aniline-functionalized graphene-polyaniline composite (a-G-PANI) is synthesized by covalent bonding and polymerization of aniline onto p-aniline functionalized graphene (a-G) substrate. To achieve this purpose, a-G substrate is initially synthesized via an easily-processible and powerful p-phenylenediamine diazotisation reaction, the modified p-aniline groups further serve as initiation sites for the chemical grafting and polymerization of aniline. The as-prepared a-G-PANI exhibits planar configuration with rich pores, which is formed by the conjugated bonding and coating of PANI nanofibers onto graphene sheet, endowing the composite with essential merits including high conductivity, efficient electrolyte diffusion channel and exposure of highly pseudocapacitive PANI to electrolyte, hence, a combined electric double-layer (EDL) capacitance and pseudocapacitance property is achieved. Supercapacitor based on a-G-PANI(200) composite with a-G to PANI ratio of 1:200 demonstrates high electrochemical capacitance (422 F g(-1)) at discharge rate of 1 A g(-1), which is dramatically higher than that based on sole a-G or PANI. The rate performance and cycling stability of a-G-PANI(200) based supercapacitor are also enhanced relative to sole PANI based counterpart, highlighting the structural advantage of chemically grafted a-G-PANI for capacitor applications. (C) 2014 Elsevier Ltd. All rights reserved.