One pot synthesis of nitrogen-doped hierarchical porous carbon derived from phenolic formaldehyde resin with sodium citrate as activation agent for supercapacitors

Nitrogen-doped hierarchical porous carbon materials were simply prepared from phenolic formaldehyde resin using sodium citrate as activation agent and hexamethylenetetramine as nitrogen source. The hierarchical porous structure of the obtained carbon samples is helpful for ion transport and greatly promote the capacitance properties of the carbon materials. The physical and chemical properties tests show that the as-prepared materials have characteristics of amorphous carbons. The low-temperature N₂ sorption experiment shows that the maximum BET specific area of the as-prepared samples can be up to 1256 m² g⁻¹, with an ideal hierarchical porous structure comprised of a large number of micropores and a certain amount of mesopores and macropores. X-ray photoelectron spectroscopy demonstrates the NHPCs have high doping (1.56–6.19 wt%) and oxygen content (6.43–11.88 at.%). Benefitting from both the high specific surface area and distinct hierarchical porous structure, the obtained samples exhibit excellent electrochemical performances when used as electrode materials. The optimal sample exhibits a high specific capacitance (C_SP) of 261 F g⁻¹ at a 0.05 A g⁻¹, with a good rate capability of 71% (185 F g⁻¹ at 20 A g⁻¹). The carbon material also shows an excellent long cycle stability (98% capacitance retention after 5000 cycles). All results indicate that the work sheds light on the technological innovation in carbon materials for energy storage.