N-doped carbons are widely used in the energy storage and conversion field because of their excellent electrical conductivity, high specific surface area, and superb electrochemical stability. Herein, high-efficiency carbon material has been derived using the kraft pulping residues – black liquor as the carbon source. The carbon material was prepared from black liquor through a two-step process, including chemical activation with NaOH at high temperature and doping with nitrogen using dicyandiamide (DCDA). The synthesized catalyst's morphology, structure, and composition were characterized using TEM, XPS, Raman Spectroscopy, and ICP-OES. The electrochemical performance has been evaluated using cyclic voltammetry (CV) and galvanostatic charge-discharge (GCD) techniques.

The synthesized nitrogen-doped carbon material had a high specific surface area of 2481 m² g⁻¹. Moreover, this catalyst had a high nitrogen content of 4.33 at%. Most of the nitrogen was in the pyridinic-N (66.58 at%) and graphitic-N forms (33.42 at%). It was found that the specific capacitance of catalysts depends on the catalyst loading. The specific capacitance of ca. 50 F g^-1 was achieved in the 1 M Na₂SO₄ aqueous solution at the scan rate of 5 mV s^-1. Besides, the specific capacitance retention was 99% after 100 cycles indicating good electrochemical stability. Our present results demonstrated that kraft pulping residue, such as black liquor, can be employed as a promising carbon precursor to synthesize low-cost and efficient catalysts for supercapacitors.

Acknowledgment

This project has received funding under the Baltic Research Programme project “Sustainably produced nanomaterials for energy applications (SuNaMa)” (No. S-BMT-21-12, LT08-2-LMT-K-01-055).