Synthesis of mesoporous NiCo₂O₄ fibers and their electrocatalytic activity on direct oxidation of ethanol in alkaline media

Highlights: • Mesoporous NiCo₂O₄ fibers were synthesized by a simple template-free method. • The NiCo₂O₄ fibers displayed fibrous morphology with well-distributed mesopores. • The mesoporous NiCo₂O₄ fibers were used as anodes for direct ethanol fuel cells (DEFCs). • The NiCo₂O₄ fibers exhibited excellent electrocatalytic activity for ethanol oxidation. • A notable reduction was found in the onset potential on NiCo₂O₄ electrodes. - Abstract: Well-dispersed mesoporous NiCo₂O₄ fibers as anode catalysts for the electrooxidation of ethanol were synthesized by an easy-controlled template-free method. Their structure and morphology were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), and N₂ adsorption/desorption analysis. The electrochemical oxidation of ethanol on mesoporous NiCo₂O₄ fibers modified glassy carbon electrode (NiCo₂O₄/GCE) in alkaline solutions was systematically evaluated by cyclic voltammetry (CV), double-step chronoamperometry (CA) and electrochemical impedance spectroscopy (EIS). The NiCo₂O₄ materials showed typical intertwined porous nanofibrous structures with specific surface area of 54.469 m² g⁻¹ and average pore size of 13.5 nm. The NiCo₂O₄/GCE exhibited significantly high electrocatalytic activity with higher current density and lower onset potential compared to those of Co₃O₄ and NiO in CV measurement. The linear relationship between the ethanol concentration and the square root of scan rate indicated that diffusion of ethanol is a rate-determining step in its oxidation on mesoporous NiCO₂O₄ fibers. The electrochemical mechanism of ethanol oxidation on NiCo₂O₄/GCE was also proposed