Ultrasound-Microwave-Assisted Synthesis of MnO2 Supercapacitor Electrode Materials

Porous manganese dioxide (MnO2) was synthesized via an ultrasoundmicrowave-intensified precipitation reaction with the soft template of triblock polymer P123. The MnO2 particles prepared by combining microwave heating and ultrasonic dispersing showed a loose sphere-network structure with tiny pores 45 nm in diameter inside the spheres, as well as architectural mesopores and macropores among the secondary particles. The loose network structure became more solid with bigger particles and less surface area if the microwave heating or ultrasonic dispersing was replaced by conventional hot plate heating or magnetic stirring. The electrochemical properties examined by cyclic voltammetry (CV) and galvanostatic charge/discharge methods illustrated that the MnO2 prepared with intensified precipitation had the highest discharge specific capacitance of similar to 214 F/g and showed negligible capacitance decline after 1000 cycles and acceptable decline after 5000 cycles, which further confirmed the combined intensifying effects of microwave heating and ultrasonic dispersing on the synthesis of MnO2 particles with higher performance.