In-Situ Gas Exfoliation Chemistry Engineering of Oxygen/Nitrogen-Functionalized Porous Carbon Nanosheet Frameworks for Supercapacitors

Oxygen (O)/nitrogen (N) codoped porous carbons are promising electrode materials for supercapacitors. The simultaneous construction of the O/N functionalized sites and efficient porous structure remains challenging. Herein, a novel in situ gas exfoliation chemistry engineering, including self-assembly synthesis and NaNO₃/CaC₂O₄ activation, is designed to construct an O/N functionalized lignosulfonate sodium (LS)-derived porous carbon nanosheet framework. Ca²⁺ ions first coordinate with -SO₃/-OH groups to disperse LS, and then partially combine with C₂O₄²⁻ ions to form elliptical CaC₂O₄@LS. NaNO₃ is precipitated within CaC₂O₄@LS to form uniformly mixed precursor. The uniform mixing enhances NaNO₃ and CaC₂O₄ activation to construct a porous carbon nanosheet framework (LPCA-Ca-Na) with 0.7-0.9 and 1-2 nm micropores, 8-200 nm meso-macropores, and high C═O (6.0 at. %) and edge N (6.3 at. %) contents. LPCA-Ca-Na delivers a high capacitance of 369 F g⁻¹ at 0.5 A g⁻¹, good rate capability, and outstanding cycling stability, due to the high micropore volume and high C═O and edge N contents providing sufficient adsorption sites and meso-macropores accelerating kinetics. The symmetric supercapacitor achieves a high energy density of 17 Wh kg⁻¹ at 238 W kg⁻¹ and excellent temperature adaptability. This work demonstrates a sustainable strategy for the efficient preparation of O/N-doped lignin-derived porous carbons for supercapacitors.