Structural and vibrational characteristics of MnFe2O4 spinal ferrites for electrochemical hydrogen evolution reaction

The depletion of fossil fuels and rising global energy demand highlight the urgent need for green alternatives such as hydrogen. Developing low-cost, efficient electrocatalysts remains a key challenge for sustainable hydrogen production via water splitting. This study investigates the synthesis and electrocatalytic performance of MnFe2O4 spinel ferrite nanoparticles for the hydrogen evolution reaction (HER). The nanoparticles were synthesized via the sol-gel method and characterized using X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), attenuated total reflectance Fourier-transform infrared spectroscopy (ATR-FTIR), Brunauer–Emmett-Teller (BET) surface area analysis, field-emission scanning electron microscopy (FESEM), energy-dispersive X-ray spectroscopy (EDS), and high-resolution transmission electron microscopy (HRTEM). XRD analysis revealed the formation of a cubic spinel structure, while ATR-FTIR spectra displayed characteristic metal-oxygen vibrational bands at 538 and 419 cm-1. XPS analysis revealed mixed oxidation states of Mn2+/Mn3+ and Fe2+/Fe3+, indicating the formation of redox-active heterojunctions that enhance catalytic performance. Morphological characterization revealed rough, interconnected clusters with a surface area of 36.63 m2/g and a pore volume of 0.088 cm3/g. EDX analysis confirmed the elemental composition of the MnFe2O4 sample. Electrochemical performance was evaluated in 1 M KOH at 25 °C using a MnFe2O4/NF electrode, which delivered a cathodic current density of 113.46 mA cm-2 at –1.5 V and required an overpotential of only 197.1 mV at 10 mA cm–2. The low overpotential and charge transfer resistance reveal the strong HER activity of MnFe2O4 and its promise as an efficient, stable electrocatalyst. Hirshfeld surface analysis and 2D fingerprint plots were employed to investigate the interatomic interactions governing crystal stability and surface topography of MnFe2O4. The results emphasize a highly stable structure, primarily driven by strong, directional Fe···O (61.7%) and Mn···O (26.5%) contacts, together contributing over 88% of the total packing interactions. The dense packing distorts FeO6 octahedra, creating concave, strained regions that act as structured binding pockets. This provides a sterically and electronically favorable environment for water adsorption and activation.