Design and supercapacitor applications of nitrogen, sulfur-codoped carbon foam from over-foaming-prone lignin

Abstract

This study reports a new strategy to regulate the over-foaming of lignin towards carbon foam production. By adding ammonium sulfate ((NH₄)₂SO₄) to lignin during the thermal conversion process, carbon foam precursor with uniform macrostructure independent of heating conditions are achieved. The mechanism between the interaction of lignin and (NH₄)₂SO₄ is discussed, and the resulting nitrogen (N), sulfur (S)-codoped carbon foam exhibits a hierarchical porous structure with compressive strength of 1.5 MPa and several other attractive properties as self-standing electrodes. Benefiting from the continuous and porous carbon network in addition to the N, S co-doping effect, it facilitates efficient electron transport and offers abundant active sites. The L1A2-1000–1-CF electrode in assembled symmetric solid-state supercapacitor device can deliver as high as 9070.9 mF cm⁻³ at 2 mV s⁻¹. This study provides a facile synthesis of N, S-codoped lignin-derived carbon foam electrodes, highlighting their potential in high-areal capacitance energy storage systems.