Fe2O3 nanodots supported on nitrogen-doped graphene sheets (denoted as Fe2O3 NDs@NG) with different loading masses are prepared through a facile one-pot solvothermal method. The resulting Fe2O3 NDs@NG composites exhibit outstanding electrochemical properties in aqueous KOH electrolyte. Among them, with the optimal loading mass of Fe2O3 NDs, the corresponding Fe2O3 NDs@NG-0.75 sample is able to deliver a high specific capacitance of 274 F g(-1) at 1 A g(-1) and the capacitance is still as high as 140 F g(-1) even at a ultrahigh current density of 50 A g(-1), indicating excellent rate capability. More remarkably, it displays superior capacitance retention after 100,000 cycles (about 75.3% at 5 A g(-1)), providing the best reported long-term cycling stability for iron oxides in alkaline electrolytes to date. Such excellent electrochemical performance is attributed to the right combination of highly dispersed Fe2O3 NDs and appropriately nitrogen-doped graphene sheets, which enable the Fe2O3 NDs@NG-0.75 to offer plenty of accessible redox active sites, facilitate the electron transfer and electrolyte diffusion, as well as effectively alleviate the volume change of Fe2O3 NDs during the charge-discharge process.
Keywords: cycling stability; iron oxide nanodots; nitrogen-doped graphene; rate capability; supercapacitor.