Modulating pore channels of activated carbon from biomass to assemble zinc ion hybrid supercapacitor with high specific capacitance

A notable challenge in zinc ion hybrid supercapacitor (ZiHSC) is the size discrepancy between the carbon cathode pores and the [Zn·(H2O)6]2+ (diameter of ∼0.86 nm), which weakens ionic migration kinetics and reduces energy density. To address this, wood-derived porous carbon with a hierarchical pore structure was synthesized via combined chemical and physical activation. The thermal reduction reaction between H2O steam and the marginal carbon atoms in the pre-existing pores was revealed, successfully enlarging pore diameters from 0.54 nm to 0.71 nm and 1.13 nm. The optimized electrode exhibited a specific capacitance of 412.76 F/g at the scan rate of 5 mV/s in a three-electrode system, and a specific capacity of 269.54 mAh/g at 0.2 A/g current density, and a high energy density of 210.76 Wh/kg at the power density of 1 296 W/kg (based on active material). Furthermore, it exhibited accelerated ion diffusion kinetics within the ZiHSC device and excellent cycling stability (93.55% capacity retention after 20, 000 cycles). In situ X-ray powder diffraction (XRD) and Raman spectra revealed that the enhanced charge storage mechanism was coupled with dynamic phase transitions of Zn4SO4(OH)6·5H2O crystallites on electrode surface and the adsorption of Zn2+/[Zn·(H2O)6]2+ into hierarchical pore channel during discharge. This study presents a novel approach for improving the structural and supercapacitive properties of activated carbon materials, demonstrating excellent potential for practical applications.