Trifunctional Nature of Heteroatom (B, N, S, O)-Doped Waste Diesel Soot: Turning Pollutants Into Potential Energy Catalysts for HER, OER, and ORR

Abstract

This study delves into the innovative use of multiheteroatom-doped vehicle exhaust soot as a catalyst for oxygen reduction reactions (ORR) and hydrogen/oxygen evolution reactions (OER/HER), presenting a transformative approach in energy materials. The synergistic effects of boron, nitrogen, oxygen, and sulfur (B, N, O, and S) heteroatom doping on vehicle exhaust carbon nanoparticles (CNPs) were explored thoroughly experimentally and through density functional theory (DFT) modeling, revealing the potential of these materials as tri-purpose catalysts for converting pollutants into electrocatalysts. The B-CNPs had the lowest overpotential (338 mV) at a current density of 10 mA/cm², whereas the reaction kinetics of the B–N–S-CNPs were superior, as they had the lowest Tafel slope (83.09 mV/dec). Furthermore, all the heteroatom-doped CNPs perform better in terms of the OER than pristine CNPs, as they are in the range of 1.05–1.15 V (values are deducted from the theoretical potential of OER 1.23 V vs. RHE) at a current density of 10 mA/cm². In the ORR, B–N–S-CNPs had the highest limiting current density, onset potential, and half-wave overpotential, which were 1.70 mA/cm², 0.86, and 0.64 V, respectively. In addition to these experimental investigations, DFT simulations were used to calculate the binding energy (BE), interaction energy (IE/E_ads), HOMO-LUMO energy band gap, charge transfer (CT), noncovalent interaction (NCI) plot, and QTAIM molecular graphs of the CNPs and heteroatom-doped CNPs and provided evocative outcomes as expected. This multifaceted approach integrates experimental and theoretical analyses, contributing to a comprehensive understanding of the catalytic potential of multiheteroatom-doped soot.