Conversion of Waste Tecoma Leaves into Heteroatom Doped Graphitic Carbon via a One-Step Chemical Activation Method for the Catalytic Oxygen Reduction Reaction and Supercapacitor Application

Abstract

For solid waste management and sustainable development, the conversion of waste materials into valuable feedstocks is essential. Keeping in mind the concept of “waste-to-wealth,” we have synthesized value-added microporous graphitic carbon from waste Tecoma leaves, referred to as TA, through a one-step chemical activation process and utilized it for oxygen reduction reactions (ORRs) and capacitive energy storage applications. The transformation of biomass into metal-free porous graphitic carbon having an ORR efficiency comparable to or even better than commercially available Pt/C is critical for renewable energy conversion technologies. The TA-900 sample, synthesized at 900 °C having a high surface area of 1429 m² g^–1, containing 4.41 atom % nitrogen and 4.74 atom % oxygen, demonstrated excellent ORR performance among the synthesized graphitic carbon samples at different temperatures. It showed an onset potential (E_onset) of 1 V and a limiting current density (J_L) of 6.21 mA cm^–2, comparable to 10 wt % Pt/C. Both experimental and theoretical findings suggest that the TA-900 electrocatalyst exhibited a 4e^– transfer mechanism in the electrocatalytic reduction of O₂ to H₂O. Regarding supercapacitor application, TA-900 achieved a high specific capacitance of 546 F g^–1 in acidic and 327 F g^–1 in neutral aqueous electrolyte at a current density of 1 A g^–1 in a three-electrode setup. The TA-900-based symmetrical supercapacitor (SSC) device has remarkable durability, retaining its 84% capacitance retention even after 3000 cycles at 1 A g^–1. It also achieved a notable energy density (33 Wh kg^–1 and 6.60 mWh cm^–3) and a power density (6.20 kW kg^–1 and 1320 mW cm^–3). The findings emphasize that heteroatom-doped TA-900 electrocatalysts synthesized from waste Tecoma leaves will be a promising, affordable alternative to the high-cost Pt/C catalyst used for clean energy conversion.