Facile low-temperature synthesis of hematite quantum dots anchored on a three-dimensional ultra-porous graphene-like framework as advanced anode materials for asymmetric supercapacitors

A composite consisting of well-dispersed and ultrafine hematite quantum-dots (∼2.7 nm) anchored on a three-dimensional ultra-porous graphene-like framework (denoted as Fe₂O₃-QDs-3D GF) has been designed by a facile and scalable strategy. In the composite, the ultra-porous 3D GF with high conductivity and high surface area was used as a conductive matrix with surface defective sites for the controllable growth of uniformly dispersed, ultra-small Fe₂O₃-QDs. The graphene framework can tightly hold a great amount of Fe₂O₃-QDs, thereby ensuring high utilization of active materials and the required conductivity to individual Fe₂O₃-QDs. The ultra-small-sized Fe₂O₃-QDs anchored on the 3D GF can endow the composite with a superior high surface area and enough active sites for electrochemical reactions, thus giving the composite a large specific capacitance. As expected, the as-prepared Fe₂O₃-QDs-3D GF electrode exhibited a high specific capacitance of 945 F g^-1 at 1.0 A g^-1 in a three-electrode system in 2.0 mol L^-1 KOH aqueous solution. In addition, high-performance asymmetric supercapacitors have been fabricated with Fe₂O₃-QDs-3D GF as the anode and 3D hierarchical porous graphene (HPG) as the cathode, and they showed a very high energy density of 77.7 W h kg^-1 at a power density of 0.40 kW kg^-1 and maximum power density of 492.3 kW kg^-1, as well as excellent cycling stability. © 2016 The Royal Society of Chemistry.