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<p>In this study, HfO<sub>2</sub> nanoparticles (NPs) doped with 0–10 wt% Al were synthesized using a Pechini-type sol–gel method and subsequently calcined at 900&#xa0;°C for 2&#xa0;h. The effects of Al doping on the phase transformation, optical properties, and electrochemical performance of the resulting NPs as supercapacitor electrodes were evaluated. The incorporation of Al into the HfO<sub>2</sub> lattice induced a phase transition from monoclinic to tetragonal HfO<sub>2</sub>, promoted by the formation of oxygen vacancies. These structural transformations occurred alongside a significant reduction in the NP size, from ~ 25&#xa0;nm to ~ 6.2&#xa0;nm. All the samples exhibited high UV–Vis–NIR reflectance, but the optical bandgap gradually decreased from 5.45 to 5.10&#xa0;eV as the Al content increased. Composite electrodes were fabricated by mixing HfO<sub>2</sub> and Al-doped HfO<sub>2</sub> NPs with activated carbon and were electrochemically evaluated in both three- and two-electrode configurations. The incorporation of Al significantly improved the supercapacitive performance. In particular, the electrode containing HfO<sub>2</sub> NPs doped with 10 wt% Al exhibited high specific capacitance and excellent capacitance retention.</p> Graphical Abstract <p></p>

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Phase transformation, optical properties, and supercapacitor electrode performance of Al-doped HfO2 nanoparticles synthesized by the pechini-type sol–gel method

  • 期刊论文

  • 发表日期：

    2026年4月10日

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  • S. Gálvez-Barbosa,
  • Luis A. González,
  • Juan A. Ríos-González,
  • R. López-Sandoval

摘要

In this study, HfO2 nanoparticles (NPs) doped with 0–10 wt% Al were synthesized using a Pechini-type sol–gel method and subsequently calcined at 900 °C for 2 h. The effects of Al doping on the phase transformation, optical properties, and electrochemical performance of the resulting NPs as supercapacitor electrodes were evaluated. The incorporation of Al into the HfO2 lattice induced a phase transition from monoclinic to tetragonal HfO2, promoted by the formation of oxygen vacancies. These structural transformations occurred alongside a significant reduction in the NP size, from ~ 25 nm to ~ 6.2 nm. All the samples exhibited high UV–Vis–NIR reflectance, but the optical bandgap gradually decreased from 5.45 to 5.10 eV as the Al content increased. Composite electrodes were fabricated by mixing HfO2 and Al-doped HfO2 NPs with activated carbon and were electrochemically evaluated in both three- and two-electrode configurations. The incorporation of Al significantly improved the supercapacitive performance. In particular, the electrode containing HfO2 NPs doped with 10 wt% Al exhibited high specific capacitance and excellent capacitance retention.

Graphical Abstract