Facile synthesis of reduced graphene oxide@Co3O4 composites derived from assisted liquid-phase plasma electrolysis for high-performance hybrid supercapacitors

• The assisted liquid-phase plasma electrolysis is applied for rGO@Co 3 O 4 composites. • The Co 3 O 4 can improve the accessibility of rGO@Co 3 O 4 composites to the electrolyte. • The specific capacitance of asymmetric supercapacitors can reach 72.3F/g at 1 A/g. • 88.2% of original specific capacitance for the electrode is kept after 10,000 cycles. Reduced graphene oxide@Co 3 O 4 (rGO@Co 3 O 4 ) composites are widely developed as promising electrode materials; however, their practical applications are restricted owing to their complex synthesis process. In the current work, we developed a rapid, efficient, and facile method for the one-step synthesis of rGO@Co 3 O 4 composites via assisted liquid-phase plasma electrolysis. During the plasma electrolysis process, uniform and ultrafine Co 3 O 4 particles are grown in-situ on rGO. The rGO@Co 3 O 4 composites present a specific capacitance as high as 1249.0F/g at 1 A/g and a capacitance retention of 89.7 % over 10,000 cycles in a three-electrode system. The superior electrochemical performance is ascribed to the synergistic effect of the high specific capacitance Co 3 O 4 and highly conductive rGO, which is conducive to promoting the transportation efficiency of ions/electrons and reducing the volume change of Co 3 O 4 in the charge–discharge cycle. Asymmetric supercapacitors are also assembled using rGO@Co 3 O 4 composites as the positive electrode and rGO as the negative electrode. The asymmetric supercapacitors achieve a specific capacitance of 72.3F/g at 1 A/g, display an energy density of 23.6 Wh/kg at a power density of 0.4 kW/kg, and exhibit superior cycle stability with a capacitance retention of 88.2 % over 10,000 cycles at 5 A/g. The current work provides a rapid, efficient, and facile method for the one-step synthesis of rGO-transition metal oxide electrodes as advanced energy storage devices.