Self-assembly-synergistic activation coupling strategy for preparing lignin-derived nitrogen/oxygen co-doped hierarchical porous carbons: structural regulation and supercapacitor applications

Heteroatom-doped hierarchical porous carbons are suitable electrode materials for supercapacitors. Mesopores and macropores can accelerate ion diffusion by shortening transport distance. However, the precise control of mesoporous and macroporous structures faces considerable challenges, and the optimal structure for efficient ion transport remains unclear. Herein, a self-assembly-synergistic activation coupling strategy is developed to prepare nitrogen/oxygen co-doped hierarchical porous carbons (HPCs) with tunable meso -macroporous structures from lignosulfonate sodium (LS). Ca 2+ coordinates with LS and subsequently bonds with C 2 O 4 2- , followed by the crystallization of NaNO 3 , forming LS/CaC 2 O 4 /NaNO 3 precursor. During precursor pyrolysis, LS decomposes to release CO 2 , promoting the reaction of CaC 2 O 4 and Na 2 CO 3 into Na 2 Ca(CO 3 ) 2 . NaNO 3 and Na 2 Ca(CO 3 ) 2 respectively act as activator and template, constructing hierarchical porous structures with meso -macropores. The HPCs prepared at 600 °C (HPC-600) exhibit the highest capacitances toward the adsorption of K + (368.9F g −1 at 0.5 A g −1 ) and Zn 2+ (333.8F g −1 at 0.1 A g −1 ), due to the highest 0.68 nm micropore volume and highest edge nitrogen/C O content (10.8 at.%). Meso-macroporous structure exhibits weaker K + transport capability than mesoporous structure, while can rapidly transport Zn 2+ . HPC-600 with the highest meso -macropore volume (0.872 cm 3 g −1 ) delivers inferior and excellent rate capabilities for K + and Zn 2+ adsorption, respectively. The zinc ion hybrid capacitors with HPC-600 cathode achieve high energy densities of 118.7 and 33.4 Wh kg −1 at 80 and 40000 W kg −1 , along with remarkable cycling stability (96.7% capacitance retention after 19,800 cycles).