TMAH-HCl demineralization reduces mineral-organic heterogeneity to regulate pore evolution in coal-derived porous carbon for high-voltage supercapacitors

Coal, as an abundant and low-cost carbon resource, represents an attractive precursor for the preparation of supercapacitor electrode materials. However, the complex mineral-organic matter composite structure in coal induces pronounced mineral heterogeneity, which leads to non-uniform carbon framework reconstruction and pore structure evolution during subsequent activation, thereby limiting the electrochemical performance enhancement of coal-derived porous carbon. Herein, a low-temperature sequential tetramethylammonium hydroxide (TMAH)-hydrochloric acid (HCl) demineralization strategy was proposed to regulate the mineral-organic structure of coal precursors without introducing additional metal ions. Specifically, the coal was first treated with TMAH, followed by washing to neutral pH and subsequent HCl treatment, enabling the stepwise regulation of mineral occurrence and removal of residual inorganic species. This sequential demineralization process effectively reduces the structural heterogeneity of mineral-organic matter interfaces, facilitating more homogeneous carbon framework reconstruction and coordinated pore evolution during KOH activation. The optimized porous carbon exhibits a reduced ash content from 1.28 % of raw coal to 0.67 %, together with a high specific surface area of 3141 m 2 g −1 , a total pore volume of 1.5078 cm 3 g −1 , and an average pore diameter of 1.92 nm, forming hierarchical pore structures favorable for the rapid transport and storage of organic electrolyte ions. Benefiting from the optimized pore architecture and improved ion accessibility in the TEABF 4 /AN electrolyte, the assembled symmetric supercapacitor delivers an energy density of 29.46 Wh kg −1 within a voltage window of 0–2.8 V. Furthermore, the device retains 82.2 % of its initial capacitance after 10,000 charge–discharge cycles at 2.8 V and 5 A g −1 , demonstrating enhanced cycling stability under high-voltage conditions. This work highlights the critical role of mineral-organic matter interface regulation in governing carbon structure evolution and organic ion transport kinetics, providing new insights into the green and controllable conversion of coal resources into high-performance porous carbon materials for organic electrolyte-based supercapacitors.