Fabrication of a nickel sulfide/nickel oxide heterostructure for efficient electrochemical oxidation of methanol

Abstract

As low-cost anode catalysts for the electrocatalytic oxidation of methanol, a nickel sulfide/nickel oxide (NiS/NiO) heterostructure deposited on Ni foam and its counterparts nickel sulfide (NiS) and nickel oxide (NiO) are presented in this study along with their synthesis, characterization, and electrochemical evaluation. With the use of powder X-ray diffraction (XRD), scanning electron microscopy (SEM), energy dispersive X-ray spectroscopy (EDS), transmission electron microscopy (TEM), selected area electron diffraction (SAED), X-ray photoelectron spectroscopy (XPS), Fourier transform infrared (FTIR) spectroscopy, and Brauner–Emmett–Teller (BET) analysis, the synthesized NiS and NiO were analyzed. The NiS/NiO/Ni foam was found to be a highly efficient and stable electrocatalyst, which initiated the methanol oxidation reaction (MOR) at an amazingly low potential of 0.34 V vs. Ag/AgCl. The NiS/NiO electrocatalyst outperformed its counterparts (NiS and NiO) under the same electrochemical circumstances, offering a current density of 837 mA cm⁻² at 0.6 V in 0.8 M methanol in alkaline media. The composite was studied further by varying NiS and NiO composite concentrations, methanol concentration, and the scan rate. Among the composites, NiS_0.7/NiO_0.3@Ni foam displayed the highest current density and lowest onset potential. The results were further validated using electrochemical impedance spectroscopy (EIS). It was discovered that NiS_0.7/NiO_0.3@Ni foam had the lowest charge transfer resistance among all the tested composite materials, as well as NiS and NiO. This innovation offers a desirable, highly effective, stable, and suitable non-noble metal electrocatalyst for methanol oxidation.