NiMn_2O_4 Nanosheet Arrays with Controlled Mass Loading as Pseudocapacitor Electrodes

摘要

Naiiostructured binary transition metal oxides are expected to possess better pseudocapacitive performance than that of mono-metal oxides. Herein, NiMn_2O_4 nanosheet arrays are grown on the Ni foam successfully with using the facile hydrothermal method and post-annealing. The surface morphology, composition and structure of as-synthesized products are investigated by Field emission scanning electron microscope, energy-dispersive X-ray spectroscopy and X-ray diffraction. The electrochemical performance is evaluated by cyclic voltammetry and galvanostatic charge-discharge tests. The results show that the thickness of nanosheets varied from 7 nm to 25 nm with changing the reaction temperature from 40To 220°C, the density of nanosheets are also present the increasing trend, and through which the mass loading of as-synthesized nanostructurs is controlled. The NiMn_2O_4 electrodes fabricated at higher reactiontemperature exhibit better electrochemical performance due to the raising mass loading of active electrode materials with the temperature. Moreover, the electrodes achieved at 220°C offer a highest specific capacitance of 177.2 mF/cm~2 at scan rate of 2 mV/s and good cycling stability with 89 % initial capacitance retention after 5000 cycles at a current density of 10 mA/cm2 in 1 M Na_2SO_4 electrolyte.