Facile Synthesis of Hematite Quantum‐Dot/Functionalized Graphene‐Sheet Composites as Advanced Anode Materials for Asymmetric Supercapacitors

For building high‐energy density asymmetric supercapacitors, developing anode materials with large specific capacitance remains a great challenge. Although Fe 2 O 3 has been considered as a promising anode material for asymmetric supercapacitors, the specific capacitance of the Fe 2 O 3 ‐based anodes is still low and cannot match that of cathodes in the full cells. In this work, a composite material with well dispersed Fe 2 O 3 quantum dots (QDs, ≈2 nm) decorated on functionalized graphene‐sheets (FGS) is prepared by a facile and scalable method. The Fe 2 O 3 QDs/FGS composites exhibit a large specific capacitance up to 347 F g −1 in 1 m Na 2 SO 4 between –1 and 0 V versus Ag/AgCl. An asymmetric supercapacitor operating at 2 V is fabricated using Fe 2 O 3 /FGS as anode and MnO 2 /FGS as cathode in 1 m Na 2 SO 4 aqueous electrolyte. The Fe 2 O 3 /FGS//MnO 2 /FGS asymmetric supercapacitor shows a high energy density of 50.7 Wh kg −1 at a power density of 100 W kg −1 as well as excellent cycling stability and power capability. The facile synthesis method and superior supercapacitive performance of the Fe 2 O 3 QDs/FGS composites make them promising as anode materials for high‐performance asymmetric supercapacitors.