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Mechanism of Electrochemical Deposition and Coloration of Electrochromic V2O5 Nano Thin Films: an In Situ X-Ray Spectroscopy Study.

Lu YR, Wu TZ, Chen CL, Wei DH, Chen JL, Chou WC, Dong CL - Nanoscale Res Lett (2015)

Bottom Line: Chronoamperometric analyses have indicated that the thin V2O5 film demonstrates faster intercalation and deintercalation of lithium ions than those of the thick V2O5 film, benefiting the coloration rate.Despite substantial research on the synthesis of vanadium oxides, the monitoring of electronic and atomic structures during growth and coloration of such material has not been thoroughly examined.This study improves our understanding of the electronic and atomic properties of the vanadium oxide system grown by electrochemical deposition and enhances the design of electrochromic materials for potential energy-saving applications.

View Article: PubMed Central - PubMed

Affiliation: Department of Physics, Tamkang University, New Taipei, 25137, Taiwan. porsche911959@hotmail.com.

ABSTRACT
Electrochromic switching devices have elicited considerable attention because these thin films are among the most promising materials for energy-saving applications. The vanadium oxide system is simple and inexpensive because only a single-layer film of this material is sufficient for coloration. Vanadium dioxide thin films are fabricated by electrochemical deposition and cyclic voltammetry. Chronoamperometric analyses have indicated that the thin V2O5 film demonstrates faster intercalation and deintercalation of lithium ions than those of the thick V2O5 film, benefiting the coloration rate. Despite substantial research on the synthesis of vanadium oxides, the monitoring of electronic and atomic structures during growth and coloration of such material has not been thoroughly examined. In the present study, in situ X-ray absorption spectroscopy (XAS) is employed to determine the electronic and atomic structures of V2O5 thin films during electrochemical growth and then electrochromic coloration. In situ XAS results demonstrate the growth mechanism of the electrodeposited V2O5 thin film and suggest that its electrochromic performance strongly depends on the local atomic structure. This study improves our understanding of the electronic and atomic properties of the vanadium oxide system grown by electrochemical deposition and enhances the design of electrochromic materials for potential energy-saving applications.

No MeSH data available.


Related in: MedlinePlus

In situ XAS at V K-edge for 60 s at applied potentials in the order of 0.0, 0.3, 0.6, 0.3, 0, −0.3, −0.6, −0.3, and 0 V. Insets display the enlargements of pre-peak intensities during delithiation (left) and lithiation (right)
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Fig5: In situ XAS at V K-edge for 60 s at applied potentials in the order of 0.0, 0.3, 0.6, 0.3, 0, −0.3, −0.6, −0.3, and 0 V. Insets display the enlargements of pre-peak intensities during delithiation (left) and lithiation (right)

Mentions: In situ XAS at V K-edge was performed during the coloration process upon the electrochemical reaction to gain insights into the effects of delithiation/lithiation on the oxidation states of vanadium, as well as the local atomic structure of the V2O5 thin films. Although the thinner film (deposited for 20 s) exhibits faster coloration rate than a thicker film (deposited for 60 s), the thicker film is more stable than the thinner one. Thus, the XAS spectrum of a V2O5 film deposited for 60 s is shown in Fig. 5. The insets compare the pre-peak intensities during delithiation (left panel) and lithiation (right panel) processes. Notably, two major changes under bias potential from 0 to −0.6 V caused by Li-ion intercalation in the spectral features, which were observed in the pre-edge region, were indicated as follows: a shift of pre-edge peak position to the lower energy and a decrease in pre-edge peaks. The shift to low energy was attributed to the decreased oxidation state of metal ions because of Li-ion intercalation, which can be conceptually caused by the reduced effective nuclear charge of the metal ions with decreased oxidation state. The pre-edge peak intensity clearly decreased for the bias potentials from 0 to −0.6 V, suggesting that the local structure around the V atom became more symmetrical with Li-ion intercalation. However, extracting lithium under a bias potential from −0.6 to +0.6 V changes the color of the film from deep blue to green to yellow. At −0.3, 0, and 0.6 V, the pre-edge peak of the V K-edge shifts to high energy when the film was oxidized, and partial V4+ ions change into V5+. The remaining V4+ ions reduced to V5+ at 0.6 V. The positive shift in the V K-edge indicates that the average oxidation state of V increased because of an increase in the attractive potential of the nucleus. Additionally, the increase in the pre-edge peak area corresponds to the gradually decreasing lithium content, revealing that structural symmetry was modified from Oh (V4+) to a mixture of Py (V5+). Without the in situ electrochemical cell, the above atomic/electronic structure information cannot be obtained. Overall, these results emphasize the importance of in situ X-ray spectroscopic characterization on the atomic/electronic structures of energy materials in their working condition.Fig. 5


Mechanism of Electrochemical Deposition and Coloration of Electrochromic V2O5 Nano Thin Films: an In Situ X-Ray Spectroscopy Study.

Lu YR, Wu TZ, Chen CL, Wei DH, Chen JL, Chou WC, Dong CL - Nanoscale Res Lett (2015)

In situ XAS at V K-edge for 60 s at applied potentials in the order of 0.0, 0.3, 0.6, 0.3, 0, −0.3, −0.6, −0.3, and 0 V. Insets display the enlargements of pre-peak intensities during delithiation (left) and lithiation (right)
© Copyright Policy - OpenAccess
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC4593985&req=5

Fig5: In situ XAS at V K-edge for 60 s at applied potentials in the order of 0.0, 0.3, 0.6, 0.3, 0, −0.3, −0.6, −0.3, and 0 V. Insets display the enlargements of pre-peak intensities during delithiation (left) and lithiation (right)
Mentions: In situ XAS at V K-edge was performed during the coloration process upon the electrochemical reaction to gain insights into the effects of delithiation/lithiation on the oxidation states of vanadium, as well as the local atomic structure of the V2O5 thin films. Although the thinner film (deposited for 20 s) exhibits faster coloration rate than a thicker film (deposited for 60 s), the thicker film is more stable than the thinner one. Thus, the XAS spectrum of a V2O5 film deposited for 60 s is shown in Fig. 5. The insets compare the pre-peak intensities during delithiation (left panel) and lithiation (right panel) processes. Notably, two major changes under bias potential from 0 to −0.6 V caused by Li-ion intercalation in the spectral features, which were observed in the pre-edge region, were indicated as follows: a shift of pre-edge peak position to the lower energy and a decrease in pre-edge peaks. The shift to low energy was attributed to the decreased oxidation state of metal ions because of Li-ion intercalation, which can be conceptually caused by the reduced effective nuclear charge of the metal ions with decreased oxidation state. The pre-edge peak intensity clearly decreased for the bias potentials from 0 to −0.6 V, suggesting that the local structure around the V atom became more symmetrical with Li-ion intercalation. However, extracting lithium under a bias potential from −0.6 to +0.6 V changes the color of the film from deep blue to green to yellow. At −0.3, 0, and 0.6 V, the pre-edge peak of the V K-edge shifts to high energy when the film was oxidized, and partial V4+ ions change into V5+. The remaining V4+ ions reduced to V5+ at 0.6 V. The positive shift in the V K-edge indicates that the average oxidation state of V increased because of an increase in the attractive potential of the nucleus. Additionally, the increase in the pre-edge peak area corresponds to the gradually decreasing lithium content, revealing that structural symmetry was modified from Oh (V4+) to a mixture of Py (V5+). Without the in situ electrochemical cell, the above atomic/electronic structure information cannot be obtained. Overall, these results emphasize the importance of in situ X-ray spectroscopic characterization on the atomic/electronic structures of energy materials in their working condition.Fig. 5

Bottom Line: Chronoamperometric analyses have indicated that the thin V2O5 film demonstrates faster intercalation and deintercalation of lithium ions than those of the thick V2O5 film, benefiting the coloration rate.Despite substantial research on the synthesis of vanadium oxides, the monitoring of electronic and atomic structures during growth and coloration of such material has not been thoroughly examined.This study improves our understanding of the electronic and atomic properties of the vanadium oxide system grown by electrochemical deposition and enhances the design of electrochromic materials for potential energy-saving applications.

View Article: PubMed Central - PubMed

Affiliation: Department of Physics, Tamkang University, New Taipei, 25137, Taiwan. porsche911959@hotmail.com.

ABSTRACT
Electrochromic switching devices have elicited considerable attention because these thin films are among the most promising materials for energy-saving applications. The vanadium oxide system is simple and inexpensive because only a single-layer film of this material is sufficient for coloration. Vanadium dioxide thin films are fabricated by electrochemical deposition and cyclic voltammetry. Chronoamperometric analyses have indicated that the thin V2O5 film demonstrates faster intercalation and deintercalation of lithium ions than those of the thick V2O5 film, benefiting the coloration rate. Despite substantial research on the synthesis of vanadium oxides, the monitoring of electronic and atomic structures during growth and coloration of such material has not been thoroughly examined. In the present study, in situ X-ray absorption spectroscopy (XAS) is employed to determine the electronic and atomic structures of V2O5 thin films during electrochemical growth and then electrochromic coloration. In situ XAS results demonstrate the growth mechanism of the electrodeposited V2O5 thin film and suggest that its electrochromic performance strongly depends on the local atomic structure. This study improves our understanding of the electronic and atomic properties of the vanadium oxide system grown by electrochemical deposition and enhances the design of electrochromic materials for potential energy-saving applications.

No MeSH data available.


Related in: MedlinePlus