Incorporation of electroactive NiCo2S4 and Fe2O3 into graphene aerogel for high-energy asymmetric supercapacitor

Incorporation of electroactive Fe2O3 and NiCo2S4 (NCS) into graphene aeorgel (GA) is presented in this work. The efficient adsorption of precursor ions on the graphene oxides sheets and subsequent hydrothermal gelation yield the GA-Fe2O3 and GA-NCS composites that can be used as negative and positive electrode, respectively, for constructing a high-energy asymmetric supercapacitor (ASC). Influences of mass contents of Fe2O3 and NCS on capacitive performances of GA-Fe2O3 and GA-NCS electrodes are systematically investigated in KOH aqueous electrolyte. The uniform distribution of Fe2O3 on the graphene sheets (GS) and the NCS nanoparticles wrapped by GS provide sufficient electroactive sites for Faradaic redox reactions, while the GA interconnected with macropores offers favorable channels for electrolyte transport. Thereby, the specific capacitance of 200 F g−1 (178 C g−1) and 386 F g−1 (170 C g−1) are achieved for GA-Fe2O3 (20 wt% Fe2O3) and GA-NCS (77 wt% NCS), respectively. A coin-type capacitor built with GA-Fe2O3 as negative electrode and GA-NCS as positive electrode delivers a specific capacitance of 93 F g−1 (128 C g−1) at 0.1 A g−1, corresponding to a maximum energy density of 25 Wh kg−1 at a power density of 54 W kg−1. Meanwhile, the ASC also exhibits a good rate capability and a satisfying cycling stability with 72.3 % capacitance retention after cycling at 2 A g−1 for 5000 cycles. These results show great potentials of GA-Fe2O3 and GA-NCS electrodes in electrochemical energy storage.