Flower-like Bi 2 O 3 with enhanced rate capability and cycling stability for supercapacitors

In this paper, Bi 2 O 3 samples were prepared by a hydrothermal way. The effects of microstructure on the electrochemical properties of Bi 2 O 3 samples were studied by adjusting hydrothermal time of synthesization (2, 6, 10, 14, and 18 h) to control the microstructure. The structure, morphology, specific surface, and chemical environment of Bi 2 O 3 were characterized by XRD, SEM, BET, and XPS. XRD patterns revealed that all diffraction peaks intensity increased with the increase of reaction time and it indicates that a higher crystallization had taken place. However, continuous improvements in electrochemical properties of the samples were not found with enhancement of the crystallinity. The specific capacitance decreases with the increase of crystalline grain size. From the SEM results, as the hydrothermal time increases, it is obvious that the sample particles agglomerate to flakes and then to flowers. The sample of Bi 2 O 3 with a hydrothermal time of 10 h exhibited a high specific capacitance (980 F g −1 at 1 A g −1 ), excellent capacity retention (86.9% from 1 to 20 A g −1 ), and a good cycle stability (85.2% at 5 A g −1 after 1000 cycles). The significance of this work is that it is possible to boost the electrochemical properties of the samples by controlling the microstructures, including reducing the crystalline grain size and maintaining a proper morphology of Bi 2 O 3 particles.