Enhanced electrocatalytic performance of NiCo2O4 nanosheets and nanoribbons for methanol oxidation in alkaline media: morphology-dependent insights

Abstract

NiCo₂O₄ nanosheets and nanoribbons were synthesized by calcining Ni–Co hydroxide and Ni–Co MOF precursors at 350 °C for two hours. These precursors were first synthesized via hydrothermal and solvothermal techniques, with the goal of improving their efficiency in methanol electro-oxidation. These two different methodologies are the factors that affect the morphology and electrochemical performance of the resulting NiCo₂O₄ under the same environmental conditions. The superior characteristics of NiCo₂O₄ nanosheets, which showed high crystallinity, well-defined morphology, high porosity, and substantial surface area, were confirmed by X-ray diffraction (XRD), scanning electron microscopy (SEM), energy dispersive spectroscopy (EDS), transmission electron microscopy (TEM), and nitrogen sorption measurements. Chronoamperometry (CA), electrochemical impedance spectroscopy (EIS), and cyclic voltammetry (CV) were used in an alkaline medium to perform electrochemical assessments for methanol oxidation. Remarkably, NiCo₂O₄ nanosheets demonstrated excellent electrocatalytic activity, outperforming NiCo₂O₄ nanoribbons with a minimal starting potential (0.32 V), elevated current density (70.36 mA cm⁻²), and good electro-oxidation stability (86%). Their distinct shape, which provides a high surface area and numerous functional sites for reaction, as well as enabling quick ion movement between the electrolyte and the electrode, is credited for the nanosheets' increased electrocatalytic efficiency. These results emphasize the potential of NiCo₂O₄ nanosheets as electroactive catalysts for fuel cell applications.