Raspberry-like hollow carbon spheres: A promising electrode material for high-performance zinc-ion hybrid supercapacitors

We report a green and scalable one-pot synthesis of raspberry-like hollow carbon spheres (HCSs) as high-performance cathode materials for zinc-ion hybrid supercapacitors (ZIHSCs). Utilizing poly(methyl methacrylate)@polypyrrole (PMMA@PPy) core-shell nanoparticles as precursors and sodium carbonate (Na₂CO₃) as both a barrier and activator, the resulting HCSs exhibit a hierarchical pore structure, a high surface area of 1883 m²/g, and significant oxygen (6.9 atom%) and nitrogen (1.7 atom%) doping. These features enable exceptional electrochemical performance, with a specific capacitance of 257 F/g at 1 A/g in a 6 M KOH electrolyte and remarkable energy density of 125 Wh/kg at a power density of 160 W/kg in ZIHSCs with a 2 M Zn(CF₃SO₃)₂ electrolyte. Moreover, the HCSs exhibit outstanding cycling stability, retaining 92.6 % of their initial capacitance after 5000 cycles at 5 A/g. This study highlights the potential of environmentally friendly porous carbon materials as promising candidates for advanced electrochemical energy storage applications.