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<p>A medium-entropy spinel ferrite, Zn<sub>0.2</sub>Cd<sub>0.2</sub>Mn<sub>0.6</sub>Fe<sub>2</sub>O<sub>4</sub>, was synthesized via the sol-gel method using polyvinyl alcohol (PVA) as a surfactant. The resulting material was thoroughly characterized using XRD, ATR-FTIR, XPS, HRTEM, FESEM, EDS, and BET analyses. XRD analysis confirmed the successful synthesis of single-phase nanocrystalline powders exhibiting a cubic spinel structure (Fd-3&#xa0;m), with an observed increase in the lattice parameter. XPS analysis reveals the incorporation of Zn<sup>2+</sup> and Cd<sup>2+</sup> into the Zn<sub>0.2</sub>Cd<sub>0.2</sub>Mn<sub>0.6</sub>Fe<sub>2</sub>O<sub>4</sub> lattice, along with the coexistence of Mn<sup>2+</sup>/Mn<sup>3+</sup> and Fe<sup>2+</sup>/Fe<sup>3+</sup> redox species. These mixed-valence states contribute to the formation of heterojunctions, which enhance the hydrogen evolution reaction (HER) activity and stability. FESEM imaging revealed granular and uneven surface morphology, while HRTEM analysis confirmed the presence of compact, irregularly shaped nanogranules. Zn<sub>0.2</sub>Cd<sub>0.2</sub>Mn<sub>0.6</sub>Fe<sub>2</sub>O<sub>4</sub> exhibited a mesoporous structure, characterized by a surface area of 36.63&#xa0;m²/g and a pore volume of 0.088&#xa0;cm³/g. The HER performance of the Zn<sub>0.2</sub>Cd<sub>0.2</sub>Mn<sub>0.6</sub>Fe<sub>2</sub>O<sub>4</sub>/NF electrode was evaluated in 1&#xa0;M KOH at 25&#xa0;°C using cathodic polarization and electrochemical impedance spectroscopy (EIS). The Zn<sub>0.2</sub>Cd<sub>0.2</sub>Mn<sub>0.6</sub>Fe<sub>2</sub>O<sub>4</sub>/NF electrode exhibited superior HER performance, delivering 58.53&#xa0;mA cm<sup>− 2</sup> at − 1.4&#xa0;V with a low overpotential of 210.1 mV at 10&#xa0;mA cm<sup>− 2</sup>. Its high catalytic efficiency was supported by low charge transfer resistance (R<sub>ct</sub>), indicating efficient interfacial charge transport. The enhanced double-layer capacitance (C<sub>dl</sub> = 4.02 mF cm<sup>− 2</sup>) for Zn<sub>0.2</sub>Cd<sub>0.2</sub>Mn<sub>0.6</sub>Fe<sub>2</sub>O<sub>4</sub>/NF can be attributed to the synergistic effects of multivalent transition metal redox couples and entropy-induced cationic disorder. Complementary structural modeling and Hirshfeld surface analysis further elucidated cation site occupancy and interatomic interactions vital to catalytic stability.</p>

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Electrochemical and Structural Insights into Zn0.2Cd0.2Mn0.6Fe2O4 Medium-Entropy Spinel Ferrite for Hydrogen Evolution Reaction in Alkaline Media

  • 期刊论文

  • 发表日期：

    2025年8月19日

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  • Ibraheem O. Ali,
  • Tarek M. Salama,
  • H. Nady,
  • H. H. Mohamed

摘要

A medium-entropy spinel ferrite, Zn0.2Cd0.2Mn0.6Fe2O4, was synthesized via the sol-gel method using polyvinyl alcohol (PVA) as a surfactant. The resulting material was thoroughly characterized using XRD, ATR-FTIR, XPS, HRTEM, FESEM, EDS, and BET analyses. XRD analysis confirmed the successful synthesis of single-phase nanocrystalline powders exhibiting a cubic spinel structure (Fd-3 m), with an observed increase in the lattice parameter. XPS analysis reveals the incorporation of Zn2+ and Cd2+ into the Zn0.2Cd0.2Mn0.6Fe2O4 lattice, along with the coexistence of Mn2+/Mn3+ and Fe2+/Fe3+ redox species. These mixed-valence states contribute to the formation of heterojunctions, which enhance the hydrogen evolution reaction (HER) activity and stability. FESEM imaging revealed granular and uneven surface morphology, while HRTEM analysis confirmed the presence of compact, irregularly shaped nanogranules. Zn0.2Cd0.2Mn0.6Fe2O4 exhibited a mesoporous structure, characterized by a surface area of 36.63 m²/g and a pore volume of 0.088 cm³/g. The HER performance of the Zn0.2Cd0.2Mn0.6Fe2O4/NF electrode was evaluated in 1 M KOH at 25 °C using cathodic polarization and electrochemical impedance spectroscopy (EIS). The Zn0.2Cd0.2Mn0.6Fe2O4/NF electrode exhibited superior HER performance, delivering 58.53 mA cm− 2 at − 1.4 V with a low overpotential of 210.1 mV at 10 mA cm− 2. Its high catalytic efficiency was supported by low charge transfer resistance (Rct), indicating efficient interfacial charge transport. The enhanced double-layer capacitance (Cdl = 4.02 mF cm− 2) for Zn0.2Cd0.2Mn0.6Fe2O4/NF can be attributed to the synergistic effects of multivalent transition metal redox couples and entropy-induced cationic disorder. Complementary structural modeling and Hirshfeld surface analysis further elucidated cation site occupancy and interatomic interactions vital to catalytic stability.