The preparation of rod-like porous α-Fe2O3 with large interplanar spacing for symmetric supercapacitors

Rod-like porous α-Fe2O3 was synthesized by static hydrothermal treatment at 160°C and used as a symmetric supercapacitor. The phase information, structure, morphology, valence state and composition of the prepared sample were characterized using X-ray diffraction, infrared spectroscopy, Raman spectroscopy, X-ray photoelectron spectroscopy, scanning electron microscopy, transmission electron microscopy and N2 adsorption–desorption. The results show that the prepared α-Fe2O3 is a rod-like porous material dominated by mesopores. Moreover, the α-Fe2O3 is a hexagonal single crystal with [FeO6] octahedrons and the interplanar crystal spacings are large enough for electrolyte ion diffusion. In both KOH and Na2SO4 electrolytes, the α-Fe2O3 sample displays good pseudocapacitance performance. However, the specific discharge capacity and energy density in KOH are larger than in Na2SO4. In 1 mol L–1 of KOH, remarkable capacities of 139 and 35.5 F g–1 are obtained and an energy density of 3.91 and 1.01 Wh kg–1 is achieved at 1 and 20 A g–1 respectively. After 10 000 cycles, 87.7% of the specific capacitance is still retained at 1 A g–1. The good capacitance properties may attributed to the rod-like porous structure and large interplanar spacing, which provide good ion insertion–exit paths, enough oxidation–reduction active sites and a fast ion transfer velocity.