Abstract Aqueous zinc-ion hybrid supercapacitors (ZIHCs) with conventional activated carbon cathodes mainly rely on electric-double-layer storage, limiting energy density and electrochemical performance. Although heteroatom doping can tailor electronic structures, introduce active sites, and enhance pseudocapacitance, it often intensifies self-discharge. Herein, DFT calculations show that N/O codoping synergistically regulates the local electronic structure and magnetic-moment distribution of activated carbon, enhances electron localization around N–O–C configurations, and lowers Zn²⁺ adsorption energy, thereby strengthening Zn-ion adsorption and charge storage. It also reduces the diffusion barrier of hydrated Zn(H2O)62+ ions in carbon slit pores, promoting rapid ion transport. Guided by this mechanism, an N/O-codoped hierarchical porous carbon cathode was prepared from banana-peel biomass using melamine as an external nitrogen source. The optimized cathode combines accessible pores, abundant active sites, and favorable ion-transport kinetics, enabling high-capacity storage with suppressed self-discharge. The assembled ZIHC delivers 540.5 F g-1 at 0.1 A g-1 and 160 Wh kg-1 at 192.18 W kg-1, retains 85.5% capacity after 5000 cycles, and maintains 93.7% voltage retention during the 2–12 h rest period. This work offers a rational route toward high-energy, fast-transport, and low-self-discharge aqueous ZIHCs.