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 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. Nitrogen functionalities and quinone groups play a critical role in enhancing charge storage. Conversely, materials abundant in carboxylic acid species may hinder electric double-layer formation, thereby limiting electrical storage. N-doped tannin-derived carbons 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.