P-doped porous carbon derived from walnut shell for zinc ion hybrid capacitors

Zinc ion hybrid capacitors (ZHCs) are expected to be candidates for large-scale energy storage products due to their high power density and large energy density. Due to their low cost and stability, carbon materials are generally the first choice for the cathode of ZHCs, but they face a challenge in the serious self-discharge behavior. Herein, zinc ion hybrid capacitors with high-performance are successfully assembled using a porous carbon cathode derived from low-cost p-doped waste biomass and a commercial zinc foil anode. The p-doped walnut shell ZHCs delivered a specific capacity of 158.9 mA h g^-1 with an energy density of 127.1 W h kg^-1 at a low current density. More importantly, the device had outstanding anti-self-discharge characteristics (retaining 77.98% of its specific capacity after a 72 h natural self-discharge test) and long-term cycle stability (retaining 88.2% of its initial specific capacity after 15 000 cycles at 7.5 A g^-1). This work presents guidance and support for the design and optimization of electrode materials for zinc ion supercapacitors and next-generation aqueous zinc ion energy storage performance.