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

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.