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<p>An intimately mixed hydroxyapatite/cobalt tungstate (HA/CoWO<sub>4</sub>) nanocomposite was prepared via a sol–gel-assisted mixing and thermal treatment approach and systematically evaluated as a multifunctional electrode for high-performance supercapacitors. Comprehensive structural [x-ray diffraction (XRD)], vibrational [Fourier-transform infrared (FTIR)], surface chemical [x-ray photoelectron spectroscopy (XPS)], and morphological [field-emission scanning electron microscopy (FESEM)/energy-dispersive x-ray (EDX)] characterizations verified the coexistence of stoichiometric hexagonal HA and monoclinic CoWO<sub>4</sub> phases with intimate interparticle contact and evidence of interfacial interaction inferred from XPS and morphology analyses. The presence of mixed Co<sup>2+</sup>/Co<sup>3+</sup> valence states and hydroxylated oxygen species contributes to rapid and reversible redox transitions, enhancing interfacial charge mobility. Electrochemical evaluations in a symmetric two-electrode configuration using 6&#xa0;M KOH electrolyte revealed pronounced pseudocapacitive behavior with contributions from both surface-controlled faradaic reactions and diffusion-regulated processes. The HA/CoWO<sub>4</sub> electrode delivered a specific capacitance of 319.29&#xa0;F&#xa0;g<sup>−1</sup> and an energy density of 15.96&#xa0;Wh&#xa0;kg<sup>−1</sup> at 0.5&#xa0;A&#xa0;g<sup>−1</sup>, outperforming pristine HA and CoWO<sub>4</sub>. Nyquist analysis demonstrated a significant decrease in both equivalent series resistance (<i>R</i><sub>ESR</sub> = 3.23&#xa0;Ω) and charge-transfer resistance (<i>R</i><sub>ct</sub> = 10.33&#xa0;Ω), confirming superior ionic diffusion and electronic conductivity. Furthermore, the device retained 90.88% of its initial capacitance after 5000 cycles, evidencing excellent electrochemical endurance. Kinetic analysis based on the power-law relationship (<i>i</i> = <i>aν</i><sup>b</sup>) yielded a <i>b</i>-value of 0.71 for the composite, indicating a mixed charge-storage mechanism rather than a purely surface-dominated process. The intimate integration of HA with the redox-active CoWO<sub>4</sub> phase provides enhanced electroactive interfaces and improved interparticle charge-transfer pathways, establishing HA/CoWO<sub>4</sub> as a sustainable and cost-effective electrode for next-generation energy storage systems.</p>

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An Intimately Mixed Hydroxyapatite/CoWO4 Composite Enabling Fast and Reversible Hybrid Pseudocapacitive–Diffusion Charge Storage

  • 期刊论文

  • 发表日期：

    2026年5月19日

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  • Qamar Abuhassan,
  • Ahmed Aldulaimi,
  • O. Waleed,
  • G. PadmaPriya,
  • Subhashree Ray,
  • Y. Sasikumar,
  • Renu Sharma,
  • Bakhodir Saydullaev,
  • Mutabar Latipova,
  • Ruslanbek Siddikov,
  • Aseel Smerat

摘要

An intimately mixed hydroxyapatite/cobalt tungstate (HA/CoWO4) nanocomposite was prepared via a sol–gel-assisted mixing and thermal treatment approach and systematically evaluated as a multifunctional electrode for high-performance supercapacitors. Comprehensive structural [x-ray diffraction (XRD)], vibrational [Fourier-transform infrared (FTIR)], surface chemical [x-ray photoelectron spectroscopy (XPS)], and morphological [field-emission scanning electron microscopy (FESEM)/energy-dispersive x-ray (EDX)] characterizations verified the coexistence of stoichiometric hexagonal HA and monoclinic CoWO4 phases with intimate interparticle contact and evidence of interfacial interaction inferred from XPS and morphology analyses. The presence of mixed Co2+/Co3+ valence states and hydroxylated oxygen species contributes to rapid and reversible redox transitions, enhancing interfacial charge mobility. Electrochemical evaluations in a symmetric two-electrode configuration using 6 M KOH electrolyte revealed pronounced pseudocapacitive behavior with contributions from both surface-controlled faradaic reactions and diffusion-regulated processes. The HA/CoWO4 electrode delivered a specific capacitance of 319.29 F g−1 and an energy density of 15.96 Wh kg−1 at 0.5 A g−1, outperforming pristine HA and CoWO4. Nyquist analysis demonstrated a significant decrease in both equivalent series resistance (RESR = 3.23 Ω) and charge-transfer resistance (Rct = 10.33 Ω), confirming superior ionic diffusion and electronic conductivity. Furthermore, the device retained 90.88% of its initial capacitance after 5000 cycles, evidencing excellent electrochemical endurance. Kinetic analysis based on the power-law relationship (i = aνb) yielded a b-value of 0.71 for the composite, indicating a mixed charge-storage mechanism rather than a purely surface-dominated process. The intimate integration of HA with the redox-active CoWO4 phase provides enhanced electroactive interfaces and improved interparticle charge-transfer pathways, establishing HA/CoWO4 as a sustainable and cost-effective electrode for next-generation energy storage systems.