CO ₂ ‐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 (CO 2 ) 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 m 2 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 CO 2 activation pathway for fabricating high‐performance energy storage materials.