High-performance 2.5 V aqueous asymmetric supercapacitor based on MnO₂ nanowire/hierarchical porous carbon composite

Abstract

Aqueous supercapacitor shows a narrow operating voltage range because of the limitation of the water electrolysis, resulting in low energy density. In this work, a nanoporous MnO₂ entangled hierarchical porous carbon skeleton (simplified to MHPC) has been successfully prepared. Aqueous asymmetric supercapacitor has been assembled by employing the MHPC as a positive electrode, a hierarchical porous carbon skeleton (HPC) as a negative electrode, and a neutral Na₂SO₄ aqueous solution as electrolyte. The assembled asymmetric supercapacitor can be stably charged in an aqueous medium in a wide voltage range of 0–2.5 V and delivers a maximum energy density of 20.8Wh/kg at a power density of 0.25 kW/kg and 25 kW/kg at an energy density of 11.1 Wh/kg in a 1 M Na₂SO₄ aqueous solution. This strategy provides a new idea for developing high-energy supercapacitor.