Co-Incorporated S-Doped Graphitic Carbon Derived from Orange Peel Biowaste: An Efficient Electrocatalyst for Sustainable Water Splitting and Urea Oxidation

Abstract

The advancement of effective, robust, and cost-effective trifunctional electrocatalysts for the hydrogen evolution reaction (HER), urea oxidation reaction (UOR), and oxygen evolution reaction (OER), is essential for electrochemical energy conversion processes. This work demonstrates the synthesis of steady and practical cobalt nanoparticles on extremely porous graphitic carbon doped with sulfur using a straightforward, sustainable, economically viable, and scalable approach. The catalysts were strengthened at varying temperatures via direct pyrolysis followed by carbonization in a nitrogen-rich atmosphere. Related to further catalysts, the carbon material synthesized at 600 °C (Co-SPC600) displays superior electrochemical performance. At a 10 mA cm^–2 of current density in 1 M KOH, the electroactive catalyst Co-SPC600 requires an overpotential of 260 mV (119 mV dec^–1) for the OER and 111 mV (111 mV dec^–1) for the HER. The active catalyst Co-SPC600 demonstrates a current degradation of less than 4.2% for OER and less than 4.6% for HER, indicating sustained durability over 60 h. For overall water splitting, Co-SPC600/NF//Co-SPC600/NF operates at 1.50 V with constant progression of H₂ and O₂ at the cathode and anode, correspondingly, exhibiting a current reduction of less than 4.8% over 80 h. Furthermore, Co-SPC600/NF facilitates urea oxidation at 1.37 V in a solution of 0.33 M urea and 1 M KOH.