A green and one-step method of electrochemical alternating voltage has been utilized to form NiO quantum dots/graphene flakes (NiO-dots/Gh) for supercapacitor applications. NiO quantum dots (similar to 3 nm) are uniformly deposited on few-layer graphene surfaces by oxygen functional groups on graphene surface that is naturally utilized to bridge NiO and graphene through Ni-O-C bands, which exhibits outstanding specific capacitance 1181.1 F g(-1) at a current density of 2.1 A g(-1) and rate behavior 66.2% at 42 A g(-1) as NiO dots can be fleetly wired up to current collector through the underlying graphene two-dimensional layers. The NiO-dots/Gh composite is further undertaken in asymmetric supercapacitors with high energy density (273 Wh kg(-1) at 1562.6 W kg(-1)). (C) 2015 Elsevier B.V. All rights reserved.