Gradient Porous Carbon Superstructures for High-efficiency Charge Storage Kinetics

Abstract

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 (≈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.