Effective approaches to co-dope lignin based concave shaped carbon nanofibers with multiple elements for supercapacitors.

High-value utilization of lignin to fabricate carbon nanofibers for supercapacitors has drawn much attention due to its sustainability. However, the heterogeneity of crude lignin structure led to the comparatively poor performance of lignin-based carbon nanofibers (LCNF) as electrodes in supercapacitors. Herein, flexible and porous LCNF simultaneously doped with N, S and Zn were firstly synthesized by electrostatic spinning followed by carbonization. The obtained L-NS20-Zn15 fibers showed optimum specific capacitance of 328.6 F g at current density of 0.5 A g in the three-electrode system. The assembled supercapacitor exhibited specific capacitance of 46.8 F g at current density of 0.5 A g, and energy density of 25.8 W h kg with power density of 200 W kg, which outperformed most of the reported LCNF-based materials. After 3000 charge-discharge cycles, the capacitance retention remained 86 % of the initial value. The remarkable electrochemical performance supports the use of co-doped lignin as a promising material for energy storage.