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In order to improve specific capacitance and limit electrical resistance, high-quality exfoliated graphene decorated with transition metal (Fe, Mn, Co) oxide nanoparticles (NPs) has been successfully synthesized without the use of surfactantvia a simple, general, environmentally-friendly chemical process. The specific capacitance of as-prepared graphene/Mn3O4 composite reach 239.6 F/g, when employed as the anode material in neutral NaCl electrolyte solutions (cf. 98.2 F/g for pristine graphene and 141.4 F/g for pure Mn3O4 NPs), which indicate the synergetic effects from both graphene and attached Mn3O4 NPs. Moreover, the high conductivity of graphene eliminates the need for conductive carbon black as fillers. The current density of graphene/Mn3O4 reached as high as 4.5 A g−1 which is much higher than that of graphene oxide (GO) or reduced GO-based composites. This significant enhancement of capacitance and current density was attributed to the surfactant-free approach to hybridize graphene with transition metal oxide NPs, the excellent conductivity of pristine graphene combined with its large surface area, as well as a uniform distribution of NPs on the clean surface of conductive graphene. Thus the low-toxicity, inexpensive graphene-based hybrids show promising utility as high current density electrode materials for supercapacitor applications.