Gradient Porous Carbon Superstructures for High-efficiency Charge Storage Kinetics

Zinc-ion hybrid supercapacitors (ZHSCs) are emerging for high-efficiency energy storage. However, single-layer cathode materials often suffer from low-charge storage kinetics. Herein, an innovative gradient porous carbon superstructure with enhanced charge storage kinetics is developed, achieved by designing a concentration gradient carbon superstructure to facilitate rapid, directional ion transport and efficient ion storage. The gradient pore design with optimized micropore sizes (0.88 to 0.96 nm) and mesopore size (approximate to 4 nm) enhances the hydrated zinc ion ([Zn(H2O)6]2+) diffusion, facilitating efficient desolvation and Zn2+ ion storage. Furthermore, N/O co-doping provides pseudo-capacitance by lowering the energy barrier for C-O-Zn bond formation, increasing the defect density and conductivity of the carbon material. Further graphitization improves conductivity and wettability, while a high specific surface area (SSA) offers abundant active sites. ZHSCs fabricated with this gradient porous carbon superstructure exhibit a remarkably high energy density of 101.8 Wh kg-1 at a substantial power density of 503.6 W kg-1, outperforming the reported benchmark materials. The exceptional charge-discharge cycling stability is also demonstrated over 10 000 cycles. This work presents an effective strategy for enhancing charge storage kinetics in supercapacitors.