Lignin-derived porous carbons via nitrogen-enhanced activation for efficient supercapacitors

Abstract

Lignin, an abundant industrial by-product, has gained attention as a sustainable precursor for porous carbon electrodes in supercapacitors due to its intrinsic aromaticity and high carbon content. While nitrogen doping is known to enhance electrochemical properties, its impact on lignin char activation mechanisms and porosity development remains underexplored. This study reports a novel, microwave-assisted nitrogen doping strategy using ethanolamine, followed by optimised chemical activation leading to the formation of highly porous carbons with enhanced charge storage capabilities. The activated carbon synthesised at an optimal NaOH-to-char weight ratio of 3:1 exhibits a uniformly distributed pore structure, as confirmed by scanning electron microscopy (SEM), along with a high specific surface area of 2749 m² g^-1 and a pore volume of 1.48 cm³ g^-1. Elemental Analysis, Raman spectroscopy, and X-ray Photoelectron Spectroscopy provides information on the thermal transformation of nitrogen species upon pyrolysis, and their differential roles in the activation process. Partial least squares (PLS) analysis further confirms that nitrogen functionality loss and activator dosage both govern porosity development. Electrochemical testing using a 2 M H₂SO₄ electrolyte demonstrates a high specific capacitance of 292 F g^-1 at 0.1 A g^-1, a remarkable capacitance retention of 90 % after 4000 cycles at 2 A g^-1, and an energy density of 9.2 Wh kg^-1 at a power density of 1.1 kW kg^-1. These results further establish nitrogen-enhanced NaOH activation as an effective route for tailoring porosity and enhancing electrochemical performance, offering a sustainable pathway for the revalorization of lignin into high-performance supercapacitor electrode materials.