Zn-Doped MnO2 microflake pseudocapacitive cathode on Ni(OH)2/Ni-Foam substrate as a promising charge storage material

Abstract

Zn-doped MnO2 microflakes cathode material on Ni(OH)2/Ni foam has been synthesized and characterized as well as tested its electrochemical performances in 3 M KOH solution. The present work varies the amounts of Zn dopant in MnO2 system to improve its capability in energy storage. Material identification has been simply confirmed with XRD, SEM, TEM, and XPS analysis. It is expected the Zn dopant will induce surface defects such as ZnMn2- or ZnMn0 and oxygen vacancy, leading to enhanced charge storage efficiency. In addition, XPS analysis reveals the existence of positively charged oxygen vacancy and the surface charge of ZnMn2- or ZnMn0 induce different surface oxidation states of Mn2+ and Mn4+. The oxidation states of Mn could accommodate the redox reactions involving ion adsorption and intercalation during pseudocapacitive charge and discharge processes. Substituting Zn into Mn sites is optimized with MnZn-1.5 which reaches a specific capacitance of 1601F/g at a 0.4 VAg/AgCl in KOH solution. This work demonstrates a promising material system for supercapacitor applications using Zn doping with a simple preparation process to support a large-scale application.