Construction of self-supporting ultra-micropores lignin-based carbon nanofibers with high areal desalination capacity

Lignin is a renewable biomacromolecule that can be used as precursors for carbon materials. In this work, highly flexible lignin-based carbon nanofibers with abundant ultra-micropores are constructed via electrospinning, oxidative stabilization and carbonization. The results indicate that replacing PAN with 80 % lignin is feasible in regulating ultra-micropores. The synthesized L4P1-CNFs possess many attractive properties (e.g., pore size distribution, electrochemical and deionization property) compared with that produced from other non-renewable precursors or more-complexed processes. It shows excellent electrochemical double-layer capacitance in 6 M KOH (233 to 162 F g−1 at 0.5 to 5 A g−1) and 1 M NaCl (158 to 82 F g−1 at 0.5 to 5 A g−1) electrolytes. Upon assembling into CDI cells, the average salt adsorption rate could reach 1.79 mg g−1 min−1 at 1.2 V and 3.32 mg g−1 min−1 at 2 V in 500 mg L−1. Benefiting from the excellent flexibility, we innovatively stack four layers of L4P1-CNFs to improve the areal electrosorption capacity to 0.0817 mg cm−2 at 500 mg L−1, significantly higher than that of traditional carbon-based electrodes. The good desalination property makes lignin-based carbon nanofibers ideal for practical, low-cost capacitive deionization applications.