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<p>Tungsten (W) is considered a critical and strategic material, the recycling of which has proved extremely important due to the substantial amount of W-rich waste and rising demand for W products. This study provides a sound technological approach for efficient utilization of bulk W, achieving a high W destruction rate (<i>r</i><sub>w</sub>) of 0.3&#xa0;g·cm<sup>−2</sup>·h<sup>−1</sup> via electrochemical oxidation/ <i>in situ</i> reduction of W electrodes in oxalic acid under alternating current (AC) with varying symmetries to synthesize WO<sub>3-<i>x</i></sub> nanopowders (NPs). Amorphous-crystalline dual-phase reduced WO<sub>3-<i>x</i></sub> NPs featuring dense and porous nanoarchitectures were synthesized using asymmetrical and symmetrical AC, respectively. The nanoscale interconnecting flaky WO<sub>3-<i>x</i></sub> structure arises from the synergy of high anodic voltage etching and the release of H<sub>2</sub> microbubbles, boosting the exfoliation of WO<sub>3</sub> flakes. The optimized WO<sub>3-<i>x</i></sub> NP exhibits superior electrochemical and electrochromic properties, attributed to the increased surface capacitance alongside an extra contribution from intercalation pseudocapacitance. The number of WO<sub>3-<i>x</i></sub> layers deposited by the spin coating technique and the annealing temperature have a significant impact on the electrochemical and electrochromic characteristics of the WO<sub>3</sub> film. An increase in the transferred charge density (<i>Q</i>), coloring/bleaching time (<i>t</i><sub>c</sub>/<i>t</i><sub>b</sub>) values, and areal capacitance was observed, alongside a decrease in optical modulation (∆<i>T</i>) and coloration efficiency (CE) with an increasing number of WO<sub>3</sub> layers. WO<sub>3</sub> produced at a lower temperature outperforms WO<sub>3</sub> treated at 400–500&#xa0;°C, particularly in fast switching, enhanced efficiency, and reversibility. The ∆<i>T</i> of 68.7%, CE of 47.9&#xa0;cm<sup>2</sup>·C<sup>−1</sup>, areal capacitance of 53.5&#xa0;mF·cm<sup>−2</sup>, and reversibility close to 100% were achieved in H<sub>2</sub>SO<sub>4</sub> for the optimized WO<sub>3-<i>x</i></sub> film. The research aligns with the ongoing development strategy of the circular economy and validates the promising features of the efficient recycling of W-containing spent resources through an environmentally sustainable electrochemical approach.</p> Graphical Abstract <p></p>

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In situ reduced WO3-x nanopowders from bulk tungsten: one-step electrosynthesis and electrochromic energy storage application

  • 期刊论文

  • 发表日期：

    2025年8月28日

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  • Anna Ulyankina,
  • Tatyana Belichenko,
  • Mikhail Gorshenkov,
  • Aleksey Yatsenko,
  • Vasily Kaichev,
  • Nina Smirnova

摘要

Tungsten (W) is considered a critical and strategic material, the recycling of which has proved extremely important due to the substantial amount of W-rich waste and rising demand for W products. This study provides a sound technological approach for efficient utilization of bulk W, achieving a high W destruction rate (rw) of 0.3 g·cm−2·h−1 via electrochemical oxidation/ in situ reduction of W electrodes in oxalic acid under alternating current (AC) with varying symmetries to synthesize WO3-x nanopowders (NPs). Amorphous-crystalline dual-phase reduced WO3-x NPs featuring dense and porous nanoarchitectures were synthesized using asymmetrical and symmetrical AC, respectively. The nanoscale interconnecting flaky WO3-x structure arises from the synergy of high anodic voltage etching and the release of H2 microbubbles, boosting the exfoliation of WO3 flakes. The optimized WO3-x NP exhibits superior electrochemical and electrochromic properties, attributed to the increased surface capacitance alongside an extra contribution from intercalation pseudocapacitance. The number of WO3-x layers deposited by the spin coating technique and the annealing temperature have a significant impact on the electrochemical and electrochromic characteristics of the WO3 film. An increase in the transferred charge density (Q), coloring/bleaching time (tc/tb) values, and areal capacitance was observed, alongside a decrease in optical modulation (∆T) and coloration efficiency (CE) with an increasing number of WO3 layers. WO3 produced at a lower temperature outperforms WO3 treated at 400–500 °C, particularly in fast switching, enhanced efficiency, and reversibility. The ∆T of 68.7%, CE of 47.9 cm2·C−1, areal capacitance of 53.5 mF·cm−2, and reversibility close to 100% were achieved in H2SO4 for the optimized WO3-x film. The research aligns with the ongoing development strategy of the circular economy and validates the promising features of the efficient recycling of W-containing spent resources through an environmentally sustainable electrochemical approach.

Graphical Abstract