Facile synthesis of green graphite-based (Ni/Cu/N) MOF composite for a methanol oxidation reaction

Abstract

Recently, direct methanol fuel cells (DMFCs) have been regarded as the greatest energy-producing owing to their low operating temperature, high production rate of methanol, and low greenhouse gas emission. However, the energy conversion efficiency of the DMFCs is still unsatisfactory due to the slow kinetics of the fuel oxidation reaction. So, an economic electrocatalyst with high efficiency and good stability is still needed. Herein, low-cost nanocomposites of (Ni/Cu/N) MOF and palm pollen-derived G-graphite were prepared with different ratios namely, (1:1), (1:2), and (2:1) through a solvothermal reaction. The nanocomposites were characterized via X-ray diffraction (XRD), Scanning electron Microscopy (SEM), Fourier transform infrared (FTIR), Thermal gravimetric analysis (TGA), and, (Brunauer–Emmett–Teller) technique (BET). Electrodes have been tested as electro-catalysts for methanol-oxidation reaction (MOR) in a basic medium. As revealed from the cyclic voltammetry measurements, all electrodes exhibit a good response to MOR, being the nanocomposite with the ratio between (Ni/Cu/N) MOF and G-graphite (2:1) is the best with an oxidation peak current density of 55 mA/cm² at a scan rate of 50 mV/s, with an onset potential of 0.35 V, and stability reaches 96 %. The electrochemical impedance spectroscopy (EIS) test showed that the ratio (2:1) has the lowest charge transfer resistance, R_CT, of 5.21 Ω which confirms its higher electrochemical activity. This superior performance of the (Ni/Cu/N) MOF and G-graphite (2:1) over other reported MOF-based electrocatalysts is attributed to the synergistic effect of the (Ni/Cu/N) MOF electrocatalyst, wherein Ni and Cu provide redox electrocatalytic active sites for MOR while the G-graphite contributes towards the chemical stability and electrical conductivity of the electrode, respectively. The good activity and stability of the prepared electrodes suggest the potential use of these electrodes as electrocatalysts for MOR in direct methanol fuel cells (DMFCs).This study opens the venue for valorizing the natural wastes derived graphitic material as stable supporting material in Mof based composites electrodes for MOR.