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 N₂ adsorption showed that H₂SO₄ etching created porous MnO₂ with average pore size of about 4 nm and high specific surface area (315 m² 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.