Self-assembled graphene coupled hollow structured γ-Fe2O3 spheres with crystal of transition for enhanced supercapacitors

Self-assembled graphene coupled hollow-structured gamma-Fe2O3 spheres (SHFS) were synthesized using a simple hydrothermal method combined with an easy annealing route. In the SHFS crystals, alpha-Fe2O3 completely transformed into gamma-Fe2O3 upon annealing at 500 degrees C under N-2 atmosphere. SHFS-500 was also found to have a high specific surface area of 198 m(2) g(-1) and to have the characteristics of a good supercapacitor electrode material, an ultrahigh specific capacitance of 332.7 F g(-1) at a current density of 2 A g(-1), good rate capability, and excellent cycling stability. This enhanced electrochemical performance may be due to the optimal architecture of the hollow-structured gamma-Fe2O3 as a result of the extraordinary electrical conductivity of graphene sheets combined with the easy annealing at 500 degrees C.