Sulfuric acid etching for fabrication of porous MnO2 for high-performance supercapacitor

We developed a facile and efficient route to prepare highly porous nanostructure MnO2 by etching of proton-type layered manganese oxide (H-MnO2) with sulfuric acid (H2SO4). Results from TEM images and N-2 adsorption showed that H2SO4 etching created porous MnO2 with average pore size of about 4 nm and high specific surface area (315 m(2) g(-1)). With such porous structure, the obtained MnO2 exhibits a high specific capacitance of 253 F g(-1) and enhanced rate capability (62.1% capacitance retention from 0.5 to 10 A g(-1)) when comparing with the H-MnO2 precursor (154 F g(-1), 45.5%) and annealed H-MnO2 in the absence of H2SO4 (134 F g(-1), 43.3%). The excellent capacitive properties demonstrate that creation of porous structure on H-MnO2 not only provides large ion-accessible surface area for efficient charge storage, but also to some extent promotes the kinetics of electrochemical reactions. (C) 2018 Elsevier Inc. All rights reserved.