Trace K2CO3 and Na2CO3 synergistic induced CO2 activation of Zhundong coal for high-performance supercapacitors

This study proposes a green, low-cost, and efficient strategy to convert inexpensive Zhundong coal into high-performance supercapacitor electrode materials. The method employs trace amounts of a binary eutectic salt (K 2 CO 3 -Na 2 CO 3 ) to synergistically catalyze CO 2 activation, enabling the preparation of optimized carbon material (TC 700-K-Na ) under a relatively mild temperature of 700 °C. The material shows a high graphitization degree, honeycomb-like porous structure, and abundant oxygen groups, enabling outstanding electrochemical performance with a capacitance of 240.55 F g −1 at 1 A g −1 and 204 F g −1 at 20 A g −1 in a three-electrode system. In addition, the assembled symmetric supercapacitor further achieves an energy density of 10.35 Wh kg −1 at a power density of 500.13 W kg −1 , while maintaining 92.97 % capacitance retention after 10,000 cycles at 10 A g −1 . The performance enhancement is attributed to the high fluidity of Na K eutectic salts at elevated temperatures, which allows CO 2 etching to penetrate from the surface into the interior of the carbon matrix. This process enables the simultaneous construction of hierarchical porous structures and a high degree of graphitization at relatively low temperatures. Overall, this work not only reveals a novel mechanism of salt-assisted CO 2 deep activation but also provides a scalable and economically feasible pathway for the high-value utilization of coal in advanced energy storage applications. • A novel K 2 CO 3 -Na 2 CO 3 synergistic activation strategy for coal-based carbons • Activation achieved at only 700 °C with reduced corrosive salt consumption • Synergistic effect: K 2 CO 3 creates micropores, Na 2 CO 3 broadens them into mesopores. • Prepared carbon exhibits hierarchical porosity and high graphitization degree. • TC 700-K-Na delivers 10.35 Wh kg −1 with 94.83 % retention after 10,000 cycles.