Low-medium temperature coal-tar phenolic fractions are aromatic-rich carbon resources with considerable potential for conversion into value-added carbon materials. Their transformation into porous carbon electrodes offers an attractive route for coal-tar valorization; however, dense carbon frameworks formed during carbonization and the trade-off between pore development and heteroatom retention often limit capacitive performance. Herein, O/N co-doped hierarchical porous carbons (ONHPCs) were prepared from coal-tar phenolics and melamine by coupling nano-CaCO₃ templating with K₂CO₃ activation in a single carbonization-activation process. Comparative pathways involving simultaneous templating-activation, nano-CaCO₃ removal prior to K₂CO₃ activation, and nano-CaCO₃ assisted carbonization without K₂CO₃ activation were used to clarify pathway-dependent structural evolution. Nano-CaCO₃ promoted meso-macropore formation and regulated the local activation environment, whereas K₂CO₃ primarily generated micropores by chemically etching the carbon framework. Their coexistence enhanced multiscale pore connectivity while moderating excessive carbon activation and heteroatom loss. The optimized ONHPC-0.8 exhibited a specific surface area of 2037 m² g^-1, with surface N and O contents of 6.04 at.% and 6.28 at.%, respectively. Density functional theory calculations showed that pyrrolic-N/carboxyl-O sites within micropores exhibited stronger K⁺ adsorption than the corresponding external-surface sites, supporting confinement-enhanced ion adsorption. In 6 M KOH, ONHPC-0.8 delivered 443 F g^-1 at 0.5 A g^-1 and retained 71.33% of its capacitance at 30 A g^-1. The symmetric device achieved 13.25 Wh kg^-1 at 300 W kg^-1 and retained 98.28% of its initial capacitance after 10,000 cycles. These results demonstrate that coupled templating-activation effectively balances pore hierarchy, heteroatom retention, and charge-storage performance, providing a promising pathway for the high-value conversion of coal-tar phenolics into advanced carbon electrodes.

Coal-tar phenolics; template-activation coupling; hierarchical pore engineering; pore confinement; supercapacitors