▎ 摘　　要

A facile and efficient method was developed to prepare nitrogen-doped graphene hydrogels (NGHs) via a one-pot hydrothermal route with graphene oxide (GO) and urea. In the procedure, urea was used as a reducing-doping agent to continuously release NH3, and N element of which was doped into graphene lattice by three styles (pyridinic N, pyrrolic N, and graphitic/quaternary N). The NGHs have high nitrogen content (ca. 6.04-6.84%), lightweight nature (the density of hydrogel is ca. 0.81-0.94 g cm(-3)), and numerous interconnected three dimensional porous networks. Electrochemical characterizations demonstrated the good capacitive behavior (230.6 F g(-1), at 0.5 A g(-1)) and superior cycling stability (capacitance retention similar to 90% after 1200 cycles) of NGHs. The possible mechanism of assembly process of NGHs and the N insertion pathway in the hydrothermal route were also proposed. (C) 2015 Elsevier Ltd. All rights reserved.