Structural, optical and magnetic investigation of the novel double perovskite La2FeCuO6 for hydrogen energy conversion application

Abstract

In this study, we investigate the structural, optical, magnetic, and electrocatalytic properties of the double perovskite La2FeCuO6, synthesized via a conventional solid state reaction method. Structural analysis based on X-ray diffraction and Rietveld refinement reveals a predominantly monoclinic P21/n phase (93.8%) with a minor La₂CuO₄ secondary phase (6.2%), exhibiting lattice parameters a = 5.5520 Å, b = 5.5562 Å, c = 7.8448 Å, and β = 89.889. The refined crystal structure reveals significant Fe/CuO₆ octahedral distortions and further supported by X-ray absorption near-edge structure (XANES) analysis, which confirms the predominance of Fe3⁺ and Cu2⁺ oxidation states. Morphological characterization by SEM-EDS shows well-defined cubic grains with homogeneous elemental distribution. Fourier transform infrared (FTIR) spectroscopy confirms the perovskite structure, exhibiting a broad band associated with Fe–O and Cu–O stretching vibrations in Fe/CuO6 octahedra. UV–Vis diffuse reflectance spectroscopy indicates a direct optical band gap of approximately 3.45 eV, confirming its nature as a wide bandgap semiconductor. Magnetic measurements reveal ferrimagnetic behavior with unsaturated magnetization up to 70 kOe, attributed to competing Fe–O–Cu superexchange interactions, cation disorder, and Jahn–Teller-induced octahedral distortions. Electrocatalytic evaluation in alkaline medium demonstrates that La2FeCuO6 exhibits moderate hydrogen evolution reaction (HER) activity, with an overpotential of 539 mV at 10 mA cm−2, a Tafel slope of 181 mV dec−1, and stable operation during 120 h of chronopotentiometric testing. The moderate HER performance is associated with the dense ceramic microstructure, limited electrochemically active surface area, and moderate charge transfer kinetics. These results demonstrate that La2FeCuO6 is a promising model double perovskite for understanding the interplay between crystal structure, electronic configuration, magnetic ordering, and electrocatalytic activity, while providing insights for the future design of non-noble metal electrocatalysts for green hydrogen production.