Gas–Liquid Co-Deposition Fabrication of MnO2 Nanosphere and Its Capacitive Properties in Alkaline and Neutral Electrolytes

Abstract

Electrochemical capacitors may theoretically reach charging rates ranging from seconds to minutes with high power densities. The use of novel materials, the production of unique nanostructures, and the exploration of electrolytes, among other things, have substantially increased the performance of supercapacitors during the last several decades. Electrochemical capacitors employing neutral/alkaline aqueous electrolytes are safer, inexpensive and allow diversified current collectors contrast to counterparts using organic electrolytes. The key to develop high-performance supercapacitors is to find super charged electrode materials and fabricate suitable nanostructures. Here, the birnessite MnO2 with highly uniform nanosphere were successfully fabricated via facile co-deposition approach of gas–liquid phase. The symmetric supercapacitor based on MnO2 was fabricated and its capacitive properties were tested in basic and neutral electrolytes using electrochemical techniques such as voltammetry (CV), impedance (EIS), spectroscopy and galvanostatic charge–discharge. The developed capacitor exhibited weaker pseudo capacitance, but wider voltage window and improved cyclic stability in KNO3 paralleled to KOH. The specific capacitance of 145 F·g−1, 106.8 W·kg−1 power density, and energy density of 14.4 Wh·kg−1 were obtained in 3 M KNO3 at 0.25 A·g−1 current density with a capacitance loss of 9.9% after 1000 continuous cycles.