Gradient Pores Enhance Charge Storage Density of Carbonaceous Cathodes for Zn‐Ion Capacitor

Engineering carbonaceous cathode materials with adequately accessible active sites is crucial for unleashing their charge storage potential. Herein, activated meso-microporous shell carbon (MMSC-A) nanofibers are constructed to enhance the zinc ion storage density by forming a gradient-pore structure. A dominating pore size of 0.86 nm is tailored to cater for the solvated [Zn(H₂O)₆]²⁺. Moreover, these gradient porous nanofibers feature rapid ion/electron dual conduction pathways and offer abundant active surfaces with high affinity to electrolyte. When employed in Zn-ion capacitors (ZICs), the electrode delivers significantly enhanced capacity (257 mAh g^-1), energy density (200 Wh kg^-1 at 78 W kg^-1), and cyclic stability (95% retention after 10 000 cycles) compared to nonactivated carbon nanofibers electrode. A series of in situ characterization techniques unveil that the improved Zn²⁺ storage capability stems from size compatibility between the pores and [Zn(H₂O)₆]²⁺, the co-adsorption of Zn²⁺, H⁺, and SO₄ ^2-, as well as reversible surface chemical interaction. This work presents an effective method to engineering meso-microporous carbon materials toward high energy-density storage, and also offers insights into the Zn²⁺ storage mechanism in such gradient-pore structures.