Green synthesis of NiO/Fe3O4@chitosan composite catalyst based on graphite for urea electro-oxidation

Abstract

In this work, we modified the NiO-based graphite electrode by a green synthesis nanoparticles composite of magnetite@chitosan for urea electrooxidation (UEO) in 0.5 M KOH solution. Green magnetite (Fe3O4) nanoparticles were prepared with green tea extract that acts as a reducing agent. The new composite catalyst Fe3O4@Chitosan performs a dual function to improve the catalytic properties of UEO. The magnetite Fe3O4 nanoparticles increase the active sites by accelerating the electron transfer between Fe3+/Fe2+ions, while chitosan enhances urea adsorption on the electrode surface. Three graphite electrodes were prepared with different NiO and Fe3O4@Chitosan catalysts ratios under optimized conditions and denoted by Ni0.85Fe0.15, Ni0.75Fe0.25, and Ni0.65Fe0.35. The excellent catalytic parameters as maximum current density (35.4 mA cm−2), Tafel slope (69 mVdec−1), diffusion coefficient (5.759 × 10−6 cm2 s−1), and onset potential (446 mV vs. Ag/AgCl) were achieved by Ni0.75Fe0.25 electrocatalyst. The modified NiO/Fe3O4@chitosan electrocatalyst was characterized by XRD and SEM/EDEX-elemental mapping techniques characterized its morphology and chemical structures. Moreover, cyclic voltammetry, double-step Choronoamerometery, and electrochemical impedance were employed to detect the electrodes' catalytic performance. The EIS fitting parameters deduced from R(RQ)& (RQ) equivalent circuits were used to explain how the Ni/Fe ratios' can affect the charge transfer process of UOR at the prepared electrocatalysts surfaces under the applied potentials.