CO₂-Activated Starch-Derived Hierarchically Porous Carbon for High-Performance Zinc-Ion Hybrid Supercapacitors

We present an environmentally friendly strategy for synthesizing hierarchically porous carbon from starch, using carbon dioxide (CO₂) as a mild activating agent. This approach circumvents the need for corrosive chemicals, while simultaneously achieving the value-added utilization of a greenhouse gas. The porosity of the resulting material, which features a specific surface area of up to 2457 m² g^-1, can be tuned via the activation time. The carbon material demonstrates exceptional performance as the cathode in an aqueous zinc-ion hybrid supercapacitor (ZHSC) which integrates the capacity of a battery-type zinc anode with the power of a capacitor-type cathode. The high surface area ensures abundant active sites for charge storage, while the hierarchical pore network facilitates efficient ion transport. The fabricated ZHSC exhibits a specific capacitance of 259 at 0.5 A g^-1 (160 at 30 A g^-1) and an energy density of 94.1 Wh kg^-1 at a power density of 399 W kg^-1 (58.5 Wh kg^-1 at 24.5 kW kg^-1) along with cycling stability yielding 97% capacitance retention over 10,000 cycles. This work highlights a sustainable approach based on the usage of a native polymer and a mild CO₂ activation pathway for fabricating high-performance energy storage materials.