Facile hydrothermal synthesis of cubic spinel AB2O4 type MnFe2O4 nanocrystallites and their electrochemical performance

Cubic spinel MnFe2O4 nanoparticles were synthesized using a simple hydrothermal method followed by post-annealing. The effects of the reaction temperature on the crystallinity, morphology, and electrochemical performance were studied. The reaction temperature played an important role in the synthesis of highly crystalline MnFe2O4 nanoparticles. At low reaction temperatures (<160 °C), the synthesized product contained a secondary inactive Fe2O3 phase as well as MnFe2O4 nanoparticles. In contrast, pure MnFe2O4 nanoparticles were obtained at temperatures above 180 °C. Furthermore, the crystallinity of the MnFe2O4 nanoparticles was enhanced significantly by increasing the reaction temperature to 200 °C. The cubic spinel MnFe2O4 nanoparticles synthesized at 200 °C delivered a maximum specific capacitance of 282.4 F g−1 at a current density of 0.5 A g−1 in a 2 M aqueous KOH solution, and exhibited long-term cyclic stability of 85.8% capacitance retention after 2000 cycles. This was attributed to the cubic spinel ferrite nanocrystallite particles not only providing the more active sites for OH− ion diffusion but also reducing the path lengths for OH− ion diffusion. These results show that the synthesized MnFe2O4 nanoparticles are promising candidates for pseudocapacitors and other electrochemical applications.