Ultrasonic and NH4+ assisted Ni foam substrate oxidation to achieve high performance MnO2 supercapacitor

Abstract Electrodeposition has become a common technology for the preparation of MnO2 supercapacitor materials. However, it was still difficult for MnO2 to obtain high specific capacitance without any assistant technology, and most reports showed only 200-450 F g-1 as the load mass over 0.5 mg cm-2. In this work, we proposed ultrasound and NH4+ assisted one step electrodeposition to prepare high-performance MnO2 (UN-MnO2) on Ni foam and explored relevant mechanisms. We also systematically studied the influence of ultrasound, the NH4+ concentration, and the loading mass on the microstructure and electrochemical performance of MnO2. The UN-MnO2 electrode exhibits a high specific capacitance of 810 F g-1 at a current density of 1 A g-1 (1.0 mg cm-2, 630.8 mF at the scan rate of 5 mV/s). After 5000 cycles, the specific capacitance remains at 88.45% of the initial value. The assembled symmetric supercapacitor (SSC) based on UN-MnO2 electrode can reach a high energy density of 58.3 Wh kg-1 (at a power density of 508 W kg-1) and high power density of 7.8 kW kg-1 (at an energy density of 26.8 Wh kg-1). This work demonstrates a simple and low-cost method, providing a good idea for the preparation of high-performance MnO2.