MnO2 Microspheres as Self-Degraded Templates to Fabricate Hollow Urchin-Like Polyaniline Microspheres for Electrochemical Energy Storage

Abstract

Conductive polymers have great potential applications as electrode materials for supercapacitors in small energy storage devices. First, manganese sulfate (MnSO₄) was oxidized to manganese dioxide (MnO₂) microspheres with a diameter of 1.5–3.5 μm by catalysis of Ag⁺. Subsequently, polyaniline (PANI) grew in situ on the surface of MnO₂ by the dilute solution method, using MnO₂ as a self-degraded template in an acidic environment. The MnO₂ was gradually reduced to Mn²⁺ because MnO₂ acted as both an oxidant and a template for the polymerization of aniline, resulting in the formation of PANI microspheres with a hollow urchin-like structure. The as-prepared PANI, with its high specific surface area and porous properties, was considered a potential material for surface–interface chemical energy storage. Therefore, the specific capacitance of the hollow urchin-like PANI electrode could reach 531 ± 35 F/g at 5 mV/s, and the loss of specific capacitance was 41.0% when the current density increased from 1 to 10 A/g. Further analysis of the charge storage mechanism of the hollow urchin-like PANI electrode revealed that the electrode was controlled by slow kinetics, indicating that the electrode reaction was mainly controlled by the Faradaic intercalation process inside the active material. A symmetric supercapacitor device was also assembled using hollow urchin-like PANI microsphere electrodes, and the maximum energy density was about 17.92 Wh/kg at a power density of 500 W/kg.