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·(H 2 O) 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 H 2 O 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 Zn 4 SO 4 (OH) 6 ·5H 2 O crystallites on electrode surface and the adsorption of Zn 2+ /[Zn·(H 2 O) 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.