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<p>NiCo<sub>2</sub>O<sub>4</sub> nanoparticles were synthesized via a sol–gel method using polyvinylpyrrolidone (PVP) and ethylenediaminetetraacetic acid (EDTA) as structure-directing agents to investigate their influence on morphology and electrochemical performance. X-ray diffraction and Raman spectroscopy confirm the formation of a cubic spinel phase (<i>Fd3m</i>) with a preferred (311) orientation. The PVP-assisted sample exhibits higher crystallinity with a crystallite size of 27&#xa0;nm and lower microstrain (0.0023), whereas the EDTA-derived sample shows smaller crystallites (18&#xa0;nm) and higher microstrain (0.0041). Morphological analysis reveals that PVP promotes the growth of well-defined nanoflakes (50&#xa0;nm) with minimal agglomeration, while EDTA leads to clustered flower-like structures (50&#xa0;nm). BET measurements indicate superior surface area and porosity for the PVP sample (132 m<sup>2</sup> g<sup>− 1</sup>, 0.336 cm<sup>3</sup> g<sup>− 1</sup>) compared to the EDTA sample (68 m<sup>2</sup> g<sup>− 1</sup>, 0.159 cm<sup>3</sup> g<sup>− 1</sup>). XPS confirms mixed Ni<sup>2+</sup>/Ni<sup>3+</sup> and Co<sup>2+</sup>/Co<sup>3+</sup> oxidation states with stronger metal–oxygen interactions in the PVP-assisted material, suggesting fewer defects. Electrochemical tests reveal a high specific capacitance of ~ 1500&#xa0;F g⁻¹ at 5&#xa0;A g⁻¹, 60% retention at 25&#xa0;A g⁻¹, and excellent cycling stability (&gt; 98% over 5000 cycles), with energy densities of ~ 63 Wh kg⁻¹ at 206&#xa0;W kg⁻¹ and ~ 37.5 Wh kg⁻¹ at 1500&#xa0;W kg⁻¹. Dunn’s analysis reveals that the capacitive contribution increases from ~ 63.3% to ~ 81.5% with increasing scan rate, indicating that surface-controlled charge storage dominates at higher scan rates, while diffusion-controlled processes contribute significantly at lower scan rates. Overall, PVP effectively directs structural growth and enhances crystallinity, morphology, and electrochemical kinetics, resulting in superior energy storage performance compared to EDTA-assisted NiCo<sub>2</sub>O<sub>4</sub>.</p>

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Influence of structure-directing agents on morphology and electrochemical performance of NiCo2O4 nanoparticles: PVP vs EDTA

  • 期刊论文

  • 发表日期：

    2026年6月23日

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  • Saripiralla Basamma,
  • P. Vishnu Prasanth

摘要

NiCo2O4 nanoparticles were synthesized via a sol–gel method using polyvinylpyrrolidone (PVP) and ethylenediaminetetraacetic acid (EDTA) as structure-directing agents to investigate their influence on morphology and electrochemical performance. X-ray diffraction and Raman spectroscopy confirm the formation of a cubic spinel phase (Fd3m) with a preferred (311) orientation. The PVP-assisted sample exhibits higher crystallinity with a crystallite size of 27 nm and lower microstrain (0.0023), whereas the EDTA-derived sample shows smaller crystallites (18 nm) and higher microstrain (0.0041). Morphological analysis reveals that PVP promotes the growth of well-defined nanoflakes (50 nm) with minimal agglomeration, while EDTA leads to clustered flower-like structures (50 nm). BET measurements indicate superior surface area and porosity for the PVP sample (132 m2 g− 1, 0.336 cm3 g− 1) compared to the EDTA sample (68 m2 g− 1, 0.159 cm3 g− 1). XPS confirms mixed Ni2+/Ni3+ and Co2+/Co3+ oxidation states with stronger metal–oxygen interactions in the PVP-assisted material, suggesting fewer defects. Electrochemical tests reveal a high specific capacitance of ~ 1500 F g⁻¹ at 5 A g⁻¹, 60% retention at 25 A g⁻¹, and excellent cycling stability (> 98% over 5000 cycles), with energy densities of ~ 63 Wh kg⁻¹ at 206 W kg⁻¹ and ~ 37.5 Wh kg⁻¹ at 1500 W kg⁻¹. Dunn’s analysis reveals that the capacitive contribution increases from ~ 63.3% to ~ 81.5% with increasing scan rate, indicating that surface-controlled charge storage dominates at higher scan rates, while diffusion-controlled processes contribute significantly at lower scan rates. Overall, PVP effectively directs structural growth and enhances crystallinity, morphology, and electrochemical kinetics, resulting in superior energy storage performance compared to EDTA-assisted NiCo2O4.