Cation-Disordered TbNdFeCoO6 Double Perovskite: Structural, Vibrational, Magnetic, and Electrocatalytic Insights for Efficient Hydrogen Evolution Reaction

Abstract

Double perovskite oxides have emerged as promising multifunctional materials for sustainable energy applications due to their tunable structural, electronic, magnetic, and electrocatalytic properties. In this research study, the cation-disordered double perovskite TbNdFeCoO6 (TNFCO) was successfully synthesized by a conventional solid-state reaction method and systematically investigated through structural, vibrational, electronic, magnetic, and electrochemical characterization. Rietveld refinement of X-ray diffraction data confirmed the formation of a single-phase orthorhombic structure with Pnma symmetry, accompanied by significant octahedral distortion and B-site cation disorder. Raman spectroscopy revealed lattice distortions consistent with the structural analysis, while X-ray photoelectron spectroscopy (XPS) confirmed the coexistence of mixed oxidation states and the presence of oxygen vacancies. Magnetic measurements revealed complex magnetic behavior characterized by ferrimagnetic correlations at low temperatures and a positive Curie–Weiss temperature (θcw = 89.08 K), indicating dominant ferromagnetic interactions associated with competing Fe–O–Co, Fe–O–Fe, and Co–O–Co exchange pathways. The electrocatalytic hydrogen evolution reaction (HER) performance was evaluated in 1.0 M NaOH, where the TNFCO-modified electrode exhibited an overpotential of 673 mV at 10 mA·cm–2, representing a 151 mV improvement compared with bare glassy carbon, together with a Tafel slope of 221 mV·dec–1 and excellent long-term stability over 50 h of continuous operation. Electrochemical impedance spectroscopy yielded a charge-transfer resistance of 626 Ω, while double-layer capacitance measurements provided a capacitance value of 45.5 μF, corresponding to an electrochemically active surface area of 1.13 cm2. The enhanced HER activity is attributed to the synergistic effects of cation disorder, mixed-valence states, oxygen vacancies, and magnetic exchange interactions that promote electron delocalization and facilitate charge transfer. These findings establish TbNdFeCoO6 as a promising multifunctional perovskite electrocatalyst for hydrogen production under alkaline conditions.