Uniformly N, O-dopant dispersion in hierarchical porous carbon through “pre-functionalization strategy” for high-performance supercapacitor application

Biomass-derived carbon with a porous structure demonstrates great potential as an advanced material for supercapacitors. However, the rationally customizing of surface functionalities for optimized performance is still challenging. In this paper, a series of hierarchical porous carbons (HPCs) with tailored nitrogen and oxygen co-doping (N, O-HPCs) were prepared by in-situ graft polymerization of glycine (Gly) on astragalus polysaccharide (APS) and followed by activation‑carbonization. Comparing with traditional impregnation techniques, the Mannich reaction during graft polymerization enables the intentional attachment of amino-groups, which serves as nitrogen sources to the APS. Additionally, the amino-group modification reduces the carbonization energy barrier of APS. The KOH-activated carbons exhibit a uniform and high dispersion of N and O dopants, characterized by a unique hierarchical porosity that combines interconnected honeycomb channels with a wealth of micro−/ meso−/ macropores. The optimized N, O-HPC-800 exhibited a high specific capacitance of 210.0 F g⁻¹ at 0.5 A g⁻¹, good rate capability (remain 112.0 F g⁻¹ at 10 A g⁻¹), and outstanding cycling durability (95 % after 10,000 cycles). The assembled N, O-HPC-800|| N, O-HPC-800 symmetric supercapacitor also presents high energy outputs of 18 Wh·kg⁻¹ at power density of 200 W kg⁻¹.