Abstract

This study examines the effects of nitrogen and boron doping on the electrochemical performance of tannin-derived carbon materials synthesized by hydrothermal carbonization (HTC) using ammonia and boric acid, followed by CO2 activation, focusing on electrochemical capacitor (EC) improvement. HTC treatment of tannins in ammonia and boric acid solutions effectively incorporates N and B into the carbon matrix, inducing changes in chemical, textural and morphological properties. Remarkably, all CO2-activated carbon materials exhibit similar specific surface area, estimated using 2D-NLDFT-HS applied to N2 and H2 isotherms at ?196 °C, allowing a fair comparison of electrochemical behavior based on surface chemistry. Nitrogen doping improved capacitance retention and energy density, surpassing both undoped and B-doped materials despite their comparable surface areas. X-ray photoelectron spectroscopy (XPS) analysis revealed that nitrogen functionalities and quinone groups play a critical role in enhancing charge storage, coupled with boosted Faradaic interactions between them and 1 M H2SO4, the aqueous electrolyte used in this study. Conversely, materials abundant in carboxylic acid species may hinder electric double-layer formation, thereby limiting electrical storage when used as EC electrodes. N-doped, tannin-derived carbon materials displayed acceptable capacitor performance, achieving specific cell capacitance values close to 42 F?g?1 at 0.5 A?g?1, with excellent capacitance retention reaching 74 % at a high applied current of 40 A?g?1. This performance, achieved with a surface area close to 1200 m2?g?1, underscores the efficacy of nitrogen doping in enhancing EC performance of tannin-derived carbon materials as promising and sustainable electrode materials. © 2025 Elsevier Ltd