Self‐Assembled 3D Graphene‐Based Aerogel with Co 3 O 4 Nanoparticles as High‐Performance Asymmetric Supercapacitor Electrode

Using graphene oxide and a cobalt salt as precursor, a three‐dimensional graphene aerogel with embedded Co 3 O 4 nanoparticles (3D Co 3 O 4 –RGO aerogel) is prepared by means of a solvothermal approach and subsequent freeze‐drying and thermal reduction. The obtained 3D Co 3 O 4 –RGO aerogel has a high specific capacitance of 660 F g −1 at 0.5 A g −1 and a high rate capability of 65.1 % retention at 50 A g −1 in a three‐electrode system. Furthermore, the material is used as cathode to fabricate an asymmetric supercapacitor utilizing a hierarchical porous carbon (HPC) as anode and 6  M KOH aqueous solution as electrolyte. In a voltage range of 0.0 to 1.5 V, the device exhibits a high energy density of 40.65 Wh kg −1 and a power density of 340 W kg −1 and shows a high cycling stability (92.92 % capacitance retention after 2000 cycles). After charging for only 30 s, three CR2032 coin‐type asymmetric supercapacitors in series can drive a light‐emitting‐diode (LED) bulb brightly for 30 min, which remains effective even after 1 h.