Honeycomb porous MnO2 nanofibers assembled from radially grown nanosheets for aqueous supercapacitors with high working voltage and energy density

Abstract

Honeycomb porous MnO<inf>2</inf> nanofibers (HMONFs) have been prepared by solution reaction between KMnO<inf>4</inf> and electrospun carbon nanofibers (CNFs). The HMONFs are entirely composed of radially grown MnO<inf>2</inf> nanosheets with thickness about 3-7nm, which interconnect each other, forming the honeycomb pores. Formation of this unique structure occurs only at very low KMnO<inf>4</inf> concentrations and sufficiently long reaction time. The constituting MnO<inf>2</inf> nanosheets in the HMONFs are well separated with the sheet edges oriented on the surface, leading to excellent supercapacitive performance. Symmetric aqueous supercapacitors are assembled using the HMONFs and 1M Na<inf>2</inf>SO<inf>4</inf> electrolyte, which exhibits a working voltage as high as 2.2V and high energy density of 41.1Wh/kg at the power density of 3.3kW/kg. The supercapacitor capacity can be retained about 76% of its initial value after 3500 cycles, which is acceptable due to its high energy density. These results indicate that the HMONFs are of high promise in developing advanced supercapacitors with high working voltage and energy density for practical applications. © 2013 Elsevier Ltd.