Co-doped FeNbO4: Simple synthesis, DFT calculations and electrocatalytic performance for the hydrogen evolution reaction in alkaline medium

Cobalt-doped iron niobate samples, Fe ( 1−x ) Co x NbO 4 (0 ≤ x ≤ 0.20), synthesized by the solid-state reaction method, were characterized using X-ray diffraction (XRD), Raman spectroscopy, scanning electron microscopy (SEM) and energy dispersive spectroscopy (EDS). Density functional theory (DFT) calculations was employed to assign the experimental Raman modes of FeNbO 4 and for cobalt-doped iron niobate, as the Raman spectra showed no significant changes in the profile upon doping. The crystal structure was successfully refined in the monoclinic system with the P21/n space-group symmetry, containing two formula units per unit cell (Z = 2). SEM analysis revealed particles with irregular morphology, and the average crystallite size increased with cobalt doping (⟨D⟩ = 28.0 ± 1.6 μm). EDS confirmed the incorporation of cobalt into the samples. Electrochemical measurements demonstrated promising hydrogen evolution reaction (HER) activity, with an overpotential of approximately 620 mV at a current density of 10 mA/cm 2 and a Tafel slope of 156 mV/dec for the Fe 0.8 0 Co 0.2 0 NbO 4 composition. Additionally, a negligible loss of overpotential was observed after 10 consecutive hours of hydrogen evolution. These findings indicate that incorporating Co 2+ ions into the iron niobate (FeNbO 4 ) matrix significantly enhances the material's electrocatalytic performance. The promising results suggest that Co-doped FeNbO 4 , as a noble metal-free electrocatalyst, holds considerable potential for applications in sustainable hydrogen production. • Simple synthesis of Co-doped FeNbO4 via solid-state method. • Promising electrocatalytic activity for hydrogen evolution reaction. • DFT calculations confirmed Raman modes and structural stability.