Efficient Preparation of Biomass‐Based Ultra‐Thin 2D Porous Carbon Materials by In Situ Template‐Activation And Its Application in Sodium Ion Capacitors

Abstract 2D porous carbon materials have demonstrated immense potential in electrochemical energy storage, whereas the challenge of achieving their efficient preparation remains substantial. Herein, 2D carbon materials with high specific surface area (SSA), well‐developed porous structures, and controllable carbon layer thickness are successfully prepared by direct co‐pyrolysis of agroforestry biomass with potassium oxalate. It is found that the potassium oxalate acts as reactant and its decomposition product potassium carbonate acts as in situ template and activator. The potassium carbonate in the core activates the outer carbon structure to form nanopores, and regulates the thickness and the graphitization degree of the carbon material. Moreover, the N‐doping strategy seriously affects the structure of the materials. CSAN‐800 prepared with 0.2 vol.% NH₃ addition can achieve N doping and SSA improvement (1802 m² g⁻¹) without damaging the ultra‐thin 2D structure. As a cathode material of sodium ion capacitors, CSAN‐800 exhibits excellent electrochemical with particularly a high‐capacity retention (90.3%) achieved (0.1 A g⁻¹–2 A g⁻¹). The 2D porous structure, high SSA, and rich pyridine‐N content significantly enhance the ion transport, storage, and optimize the charge carrier's adsorption and desorption. This study provides a low‐cost and eco‐friendly preparation strategy for ultra‐thin 2D porous carbon materials.