Three functionalized N-doped graphene hydrogels were prepared from graphene oxide (GO) and isomers of phenylenediamine through hydrothermal process, which were (1) FONGH prepared with o-phenylenediamine (OPD); (2) FMNGH prepared with m-phenylenediamine (MPD) and (3) FPNGH prepared with p-phenylenediamine (PPD). As-prepared FONGH, FMNGH and FPNGH possessed different microstructures and exhibited different specific surface area: 107.8, 24.3 and 145.2 m(2) g(-1). The prepared graphene hydrogels were found with different N contents: FONGH (11.1 at.%) > FPNGH (9.8 at.%) > FMNGH (7.2 at.%). High resolution N 1s spectra of as-prepared hydrogels revealed that OPD facilitated the preparation of graphene with high doping level of nitrogen; while PPD was favorable to preparing N-doped graphene hydrogel with high moieties of amine including -NH2 or N covalent bonded with sp(3)-C of graphene. As-prepared FONGH, FMNGH and FPNGH exhibited excellent electrochemical performance with high specific capacitance (645, 365.7 and 467 F g(-1) at 1 A g(-1)) and superior cycling stability (97.6%, 83.1% and 91% retention at 20 A g(-1) after 1000 cycles). The different microstructures and electrochemical performance of FONGH, FMNGH and FPNGH were caused by different positions of -NH2 groups on the benzene rings of OPD, MPD and PPD. The present work proposes a novel idea to prepare functionalized N-doped graphene with high electrochemical performance. (C) 2016 Elsevier Ltd. All rights reserved.