Dual-Functional Potassium Citrate: Synergistic In Situ Carbon Filling and Activation toward Wood-Based Thick Carbon...

Electrical double-layer capacitors (EDLCs) and zinc-ion hybrid capacitors (ZHCs) are promising green energy storage devices, but their practical application is limited by low mass loading of traditional carbon electrodes, causing insufficient capacitance and low energy density. Wood-derived carbon with vertical channels is ideal for thick electrode fabrication but suffers from a poor pore structure and low channel utilization. Herein, we prepare high-mass-loading wood-based thick carbon electrodes using potassium citrate as a dual-functional modifier (chemical activator and in situ carbon precursor). Pre-oxidized basswood was vacuum-impregnated with a saturated potassium citrate solution and transformed into a carbon framework via one-step carbonization/activation at 750-900 °C. Potassium citrate decomposed to generate alkaline species for etching the carbon matrix to form a hierarchical porous structure, and its carbon-containing moieties were in situ carbonized to fill vertical channels of wood, improving channel utilization and mass loading. The optimized PC@CW-850 (850 °C) had a specific surface area of 1563 m² g^-1 and abundant oxygen groups. In a three-electrode system, it delivered an areal specific capacitance of 14,008 mF cm^-2 (292 F g^-1) at 5 mA cm^-2 with 59% retention at 200 mA cm^-2 and nearly 100% capacitance retention after 30,000 cycles. In a two-electrode EDLC, it achieved 6594 mF cm^-2 (5 mA cm^-2) and a maximum areal energy density of 0.9 mWh cm^-2. As a ZHC cathode in 2 M ZnSO₄, it exhibited 9094 mF cm^-2 at 5 mA cm^-2 with 74% retention at 100 mA cm^-2. This work provides a new strategy for designing high-mass-loading biomass-derived carbon thick electrodes and deepens the understanding of organic potassium salt modification for carbon materials.