Hollow-porous carbon microspheres with hierarchically micromesoporous shells and superhydrophilic surfaces for high-performance aqueous supercapacitors

Abstract

Hollow-porous carbon microspheres (SPC-MnO2) are synthesized using sucrose as a carbon source and MnO2 microspheres with a porous and rough surface as a template, followed by activation with KHCO3. The activation process involves anchoring carbon onto the MnO2 template while simultaneously creating pores in the carbon shell. The SPC-MnCO3 sample, which utilizes well-defined MnCO3 microspheres as a template, exhibits disintegrated grains with irregular shapes owing to the substantial decomposition of MnCO3 during activation. The SPC-MnO2 sample demonstrates a large surface area of 1589 m² g⁻¹ and a pore volume of 2.52 cm³ g⁻¹, featuring substantial amounts of mesopores ranging from 3 to 30 nm in size. The micromesoporous structure of SPC-MnO2 provides a hydrophilic surface, thereby enhancing wettability in aqueous KOH electrolytes and improving charge-storage capabilities. The SPC-MnO2 electrode exhibits superior specific capacitance (317 F g⁻¹ at 1 A g⁻¹) and high-rate performance (202 F g⁻¹ at 50 A g⁻¹) in 6 M KOH compared with microporous carbon produced without a template. The notable enhancement in supercapacitor performance can be attributed to the hollow structural integrity of the microspheres, the superhydrophilic surface, high electrical conductivity, and the hierarchical micromesoporous nature. These features facilitate efficient ion/electron transport and surface-controlled redox kinetics.