A facile and rapid candle flame treatment technique has been developed to synthesize the hybrid nanostructure of soot-based carbon nanoparticles decorated graphene sheets (CN-GS) from graphene oxide. In this technique, candle flame serves the dual purpose i.e. acting as reducing medium for the graphene oxide reduction into graphene and it also acts as a source of carbon nanoparticles. During the flame treatment, these nanoparticles get uniformly deposited on the graphene sheets. The as-prepared nanocomposite has been characterized thoroughly and studied as an electrode material for supercapacitors, aqueous Al-ion battery and capacitive deionization (CDI) applications. The CN-GS based symmetric supercapacitor device exhibits an excellent gravimetric specific capacitance of 351 F g−1 and energy density of 12.2 Wh kg−1. The electrochemical performance of this material has also been tested for the aqueous Al-ion battery cathode, where it was found to possess 152.7 mAh g−1 of specific capacity. In addition to this, CN-GS based CDI electrode exhibited the salt adsorption capacity of 30.7 mg g−1. The CN-GS should be a promising electrode material for highly efficient energy storage devices and CDI applications due to its excellent electrochemical performance and long cyclic stability.