Elektrobiriktirme yöntemiyle hazırlanan WO₃ ince filmlerin karanlık ve aydınlatılmış koşullar altında elektrokimyasal empedans spektroskopisi analizi

Abstract

Arka Plan—Tungsten oksit (WO₃), uygun optik geçirgenliği, kimyasal kararlılığı ve uygun bant aralığı nedeniyle fotoelektrokimyasal uygulamalar için umut vadeden bir malzeme olarak yaygın şekilde kabul edilmektedir. Biriktirme parametreleri ile arayüzey yük transfer davranışı arasındaki ilişkinin anlaşılması, WO₃ tabanlı cihazların performansının iyileştirilmesi açısından büyük önem taşımaktadır.

Amaç—Bu çalışmada, tungsten oksit (WO₃) ince filmler FTO kaplı cam altlıklar üzerine −0.6 V ve −0.7 V potansiyellerinde potansiyostatik elektrobiriktirme tekniği kullanılarak büyütülmüştür. Biriktirme potansiyelinin yüzey morfolojisi, optik özellikler ve fotoelektrokimyasal davranış üzerindeki etkisi sistematik olarak incelenmiştir.

Yöntem—SEM analizi, her iki filmin de homojen ve sürekli yapılara sahip olduğunu ortaya koyarken, −0.7 V’ta biriktirilen örneğin daha belirgin aglomerasyon sergilediğini göstermiştir. Bu durum, daha yüksek biriktirme potansiyellerinde artan çekirdeklenme ve büyüme kinetiğine işaret etmektedir. UV–Vis ölçümleri, her iki örneğin de görünür bölgede yüksek optik geçirgenlik (yaklaşık %70–80) sergilediğini göstermiştir. Bununla birlikte, daha yüksek yüzey pürüzlülüğüne bağlı olarak artan ışık saçılması nedeniyle −0.7 V örneğinde geçirgenlikte hafif bir azalma gözlenmiştir. Elektrokimyasal Empedans Spektroskopisi (EIS) ve Fotoelektrokimyasal Empedans Spektroskopisi (PEIS) ölçümleri karanlık koşulların yanı sıra 535 nm monokromatik ışık ve Xe lamba aydınlatması altında gerçekleştirilmiştir. Empedans verileri ayrıca yük transfer direnci ve kapasitif davranış gibi arayüzey parametrelerini değerlendirmek amacıyla eşdeğer devre modellemesi kullanılarak analiz edilmiştir.

Bulgular—Karanlık koşullarda ağırlıklı olarak kapasitif davranış gözlenirken, aydınlatma altında empedansta meydana gelen belirgin azalma, foto-indüklenmiş yük taşıyıcılarının oluşumunu ve arayüzey yük transfer süreçlerinin iyileştiğini göstermektedir. Karşılaştırmalı analiz, −0.6 V’ta biriktirilen örneğin aydınlatma altında daha düşük empedans ve daha kararlı bir arayüzey tepkisi sergilediğini, bunun da daha verimli yük transferine işaret ettiğini göstermiştir. Buna karşılık, −0.7 V’ta biriktirilen örnek, artan yüzey heterojenliği ve rekombinasyon süreçleriyle ilişkili daha karmaşık bir empedans davranışı sergilemiştir.

Sonuç—Bu sonuçlar, biriktirme potansiyelinin WO₃ ince filmlerin arayüzey kinetiğinin ve elektrokimyasal davranışının belirlenmesinde önemli bir rol oynadığını ve −0.6 V potansiyelinin daha verimli yük transferine olanak sağladığını göstermektedir. Elde edilen bulgular, WO₃ ince filmlerin arayüzey özelliklerinin kontrol edilmesinde biriktirme parametrelerinin optimizasyonunun kritik rolünü ortaya koymaktadır. Bu çalışma, EIS ve PEIS tekniklerinin WO₃ tabanlı fotoelektrokimyasal sistemlerin geliştirilmesinde vazgeçilmez karakterizasyon araçları olduğunu ortaya koymakta ve yeni nesil akıllı pencere teknolojileri ile verimli güneş enerjisi destekli hidrojen üretim sistemlerinin tasarımı için güçlü bir temel sağlamaktadır.

Keywords

• Elektrokimyasal empedans spektroskopisi (EIS)
• Elektrobiriktirme
• Fotoelektrokimyasal empedans spektroskopisi (PEIS)
• İnce film
• Tungsten oksit

Project Number

223M337, FHD-2024-21270 and FKB-2024-21248

Electrochemical impedance spectroscopy analysis of electrodeposited WO₃ thin films under dark and illuminated conditions

Abstract

Context—Tungsten oxide (WO₃) is widely recognized as a promising material for photoelectrochemical applications due to its favorable optical transparency, chemical stability, and suitable band gap. Understanding the relationship between deposition parameters and interfacial charge transfer behavior is essential for improving the performance of WO₃-based devices.

Objective—In this study, tungsten oxide (WO₃) thin films were deposited on FTO-coated glass substrates at −0.6 V and −0.7 V using a potentiostatic electrodeposition technique. The effect of deposition potential on surface morphology, optical properties, and photoelectrochemical behavior was systematically investigated.

Method—SEM analysis revealed that both films exhibit homogeneous and continuous structures, while the sample deposited at −0.7 V shows more pronounced agglomeration, indicating enhanced nucleation and growth kinetics at higher deposition potentials. UV–Vis measurements demonstrated that both samples exhibit high optical transmittance in the visible region (approximately 70–80%), whereas a slight decrease was observed for the −0.7 V sample due to increased light scattering associated with higher surface roughness. Electrochemical Impedance Spectroscopy (EIS) and Photoelectrochemical Impedance Spectroscopy (PEIS) measurements were carried out under dark conditions, as well as under 535 nm monochromatic and Xe lamp illumination. The impedance data was further analyzed using equivalent circuit modeling to evaluate interfacial parameters such as charge transfer resistance and capacitive behavior.

Results—While predominantly capacitive behavior was observed under dark conditions, a significant decrease in impedance under illumination indicates the generation of photo-induced charge carriers and enhanced interfacial charge transfer processes. Comparative analysis showed that the sample deposited at −0.6 V exhibits lower impedance and a more stable interfacial response under illumination, indicating more efficient charge transfer. In contrast, the sample deposited at −0.7 V demonstrates a more complex impedance response associated with increased surface heterogeneity and recombination processes.

Conclusion—These results demonstrate that the deposition potential plays a decisive role in determining the interfacial kinetics and electrochemical behavior of WO₃ thin films, and that a potential of −0.6 V enables more efficient charge transfer. These findings highlight the critical role of deposition parameter optimization in tailoring the interfacial properties of WO₃ thin films. This study positions EIS and PEIS techniques as indispensable characterization tools for advancing WO₃-based photoelectrochemical systems and provides a strong foundation for the design of next-generation smart window technologies and efficient solar-driven hydrogen production systems.

Keywords

• Electrochemical impedance spectroscopy (EIS)
• Electrodeposition
• Photoelectrochemical impedance spectroscopy (PEIS)
• Thin film
• Tungsten oxide

Supporting Institution

Scientific and Technological Research Council of Türkiye (TÜBİTAK) for the project with Project ID 223M337 and Hacettepe University Research Projects System for support from Project ID FHD-2024-21270 and FKB-2024-21248

Project Number

223M337, FHD-2024-21270 and FKB-2024-21248

References

1. F. H. An, Y. Z. Yuan, J. Q. Liu, M. D. He, B. Zhang, “Enhanced electrochromic properties of WO3/ITO nanocomposite smart windows”, RSC Advances, 13(19), 13177–13182, 2023. https://doi.org/10.1039/d3ra01428b.
2. S. K. Deb, “Opportunities and challenges in science and technology of WO₃ for electrochromic and related applications”, Solar Energy Materials and Solar Cells, 92(2), 245–258, 2008. https://doi.org/10.1016/j.solmat.2007.01.026.
3. Y. N. Kanafin, A. Abduvalov, M. Kaikanov, S. G. Poulopoulos, T. Sh. Atabaev, “A review on WO₃ photocatalysis used for wastewater treatment and pesticide degradation”, Heliyon, 11(1), e40788, 2025. https://doi.org/10.1016/j.heliyon.2024.e40788.
4. M. Zhang, C. Yang, Z. Zhang, W. Tian, B. Hui, J. Zhang, K. Zhang, “Tungsten oxide polymorphs and their multifunctional applications”, Advances in Colloid and Interface Science, 300, 102596, 2022. https://doi.org/10.1016/j.cis.2021.102596.
5. H. Abbas, Z. Khaliq, N. Nadeem, M. B. Qadir, M. U. Rehman, D. Umer, Z. Jilani, M. W. Shahzad, “Recent advancements in WO₃-based polymeric nanocomposites for photocatalytic applications: a comprehensive review”, Chemical Papers, 80(6), 5785-5827, 2026. https://doi.org/10.1007/s11696-026-04708-6.
6. M. I. Nabeel, D. Hussain, N. Ahmad, M. Najam-ul-Haq, S. G. Musharraf, “Recent advancements in the fabrication and photocatalytic applications of graphitic carbon nitride–tungsten oxide nanocomposites”, Nanoscale Advances, 5(19), 5214–5255, 2023. https://doi.org/10.1039/d3na00159h.
7. J. Y. Zheng, Q. Sun, J. Cui, X. Yu, S. Li, L. Zhang, S. Jiang, W. Ma, R. Ma, “Review on recent progress in WO₃-based electrochromic films: preparation methods and performance enhancement strategies”, Nanoscale, 15(1), 63–79, 2022. https://doi.org/10.1039/d2nr04761f.
8. M. Epifani, “Mechanistic insights into WO₃ sensing and related perspectives”, Sensors, 22(6), 2247, 2022. https://doi.org/10.3390/s22062247.

9. S. Poongodi, P. S. Kumar, D. Mangalaraj, P. Nagamony, P. Meena, Y. Masuda, C. Lee, “Electrodeposition of WO₃ nanostructured thin films for electrochromic and H₂S gas sensor applications”, Journal of Alloys and Compounds, 719, 71–81, 2017. https://doi.org/10.1016/j.jallcom.2017.05.122.
10. T. Xiang, Q. Xu, H. Liu, Y. Lu, “A high-performance electrochromic Mo-doped WO₃ film towards smart window”, Journal of Physics: Conference Series, 3009(1), 012018, 2025. https://doi.org/10.1088/1742-6596/3009/1/012018.
11. X. Sun, D. Wang, W. Wu, X. Zhao, X. Zhang, B. Wang, X. Rong, G. Wu, X. Wang, “Amorphous and crystalline Ti-doped WO₃·2H₂O for dual-band electrochromic smart windows”, ACS Sustainable Chemistry & Engineering, 12(14), 5459–5467, 2024. https://doi.org/10.1021/acssuschemeng.3c07679.
12. H. Zhao, X. Yu, S. Yu, H. Yang, W. Guo, S. Li, J. Y. Zheng, “Review on amorphous WO3 for electrochromic devices: structure, optimization strategies and applications”, Materials Today Chemistry, 43, 102513, 2025. https://doi.org/10.1016/j.mtchem.2025.102513.
13. International Energy Agency, “Global Hydrogen Review 2025”, Paris, France, 2025. https://www.iea.org/reports/global-hydrogen-review-2025.
14. C. G. Granqvist, “Electrochromics for smart windows: oxide-based thin films and devices”, Thin Solid Films, 564, 1–38, 2014. https://doi.org/10.1016/j.tsf.2014.02.002.
15. J. Cen, Q. Wu, D. Yan, W. Zhang, Y. Zhao, X. Tong, M. Liu, A. Orlov, “New aspects of improving the performance of WO₃ thin films for photoelectrochemical water splitting by tuning the ultrathin depletion region”, RSC Advances, 9(2), 899–905, 2019. https://doi.org/10.1039/c8ra08875f.
16. H. Habazaki, Y. Hayashi, H. Konno, “Characterization of electrodeposited WO₃ films and its application to electrochemical wastewater treatment”, Electrochimica Acta, 47(26), 4181–4188, 2002. https://doi.org/10.1016/S0013-4686(02)00435-8.
17. M. Murtaza, W. A. Shah, A. Waseem, “WO₃/Nb₂CTx MXene 2D–2D heterojunction as a high performance photoanode for photoelectrochemical water splitting”, Nanoscale Advances, 7(14), 4450–4460, 2025. https://doi.org/10.1039/d5na00345h.
18. J. Zhang, C. D. Van, K. Takei, M. H. Lee, “Three-dimensional WO₃ nanorod arrays on Si as photoanodes for efficient photoelectrochemical water splitting”, Journal of Industrial and Engineering Chemistry, 124, 550–557, 2023. https://doi.org/10.1016/j.jiec.2023.05.011.
19. International Energy Agency, “World Energy Outlook 2025”, Paris, France, 2025. https://www.iea.org/reports/world-energy-outlook-2025.
20. J. Guo, H. Jia, Z. Shao, P. Jin, X. Cao, “Fast-switching WO₃-based electrochromic devices: design, fabrication, and applications”, Accounts of Materials Research, 4(5), 438–447, 2023. https://doi.org/10.1021/accountsmr.2c00217.
21. M. G. Walter, E. L. Warren, J. R. McKone, S. W. Boettcher, Q. Mi, E. A. Santori, N. S. Lewis, “Solar water splitting cells”, Chemical Reviews, 110(11), 6446–6473, 2010. https://doi.org/10.1021/cr1002326.
22. S. J. Hong, S. Lee, J. S. Jang, J. S. Lee, “Heterojunction BiVO₄/WO₃ electrodes for enhanced photoactivity of water oxidation”, Energy & Environmental Science, 4(5), 1781–1787, 2011. https://doi.org/10.1039/c0ee00743a.
23. M. E. Orazem, B. Tribollet, Electrochemical Impedance Spectroscopy, 2nd ed., Hoboken, NJ, USA, Wiley, 2017.
24. J. Bisquert, S. Giménez, L. Bertoluzzi, I. Herraiz-Cardona, “Analysis of photoelectrochemical systems by impedance spectroscopy”, Photoelectrochemical Solar Fuel Production, S. Giménez, J. Bisquert (Eds.), Cham, Switzerland, Springer, 2016, Ch. 6, 281–321. https://doi.org/10.1007/978-3-319-29641-8.
25. E. Barsoukov, J. R. Macdonald, Impedance Spectroscopy: Theory, Experiment, and Applications, 3rd ed., Hoboken, NJ, USA, Wiley, 2018.
26. E. A. Ponomarev, L. M. Peter, “A comparison of intensity modulated photocurrent spectroscopy and photoelectrochemical impedance spectroscopy in a study of photoelectrochemical hydrogen evolution at p-InP”, Journal of Electroanalytical Chemistry, 397(1-2), 45–52, 1995. https://doi.org/10.1016/0022-0728(95)04148-9.
27. T. Hisatomi, J. Kubota, K. Domen, “Recent advances in semiconductors for photocatalytic and photoelectrochemical water splitting”, Chemical Society Reviews, 43(22), 7520–7535, 2014. https://doi.org/10.1039/c3cs60378d.
28. D. Klotz, D. A. Grave, H. Dotan, A. Rothschild, “Empirical analysis of the photoelectrochemical impedance response of hematite photoanodes for water photo-oxidation”, Journal of Physical Chemistry Letters, 9(6), 1466–1472, 2018. https://doi.org/10.1021/acs.jpclett.8b00096.
29. B. Klahr, T. Hamann, “Water oxidation on hematite photoelectrodes: insight into the nature of surface states through in situ spectroelectrochemistry”, The Journal of Physical Chemistry C, 118(19), 10393–10399, 2014. https://doi.org/10.1021/jp500543z.
30. X. Shi, I. Herraiz-Cardona, L. Bertoluzzi, P. Lopez-Varo, J. Bisquert, J. H. Park, S. Gimenez, “Understanding the synergistic effect of WO₃–BiVO₄ heterostructures by impedance spectroscopy”, Physical Chemistry Chemical Physics, 18(13), 9255–9261, 2016. https://doi.org/10.1039/c5cp07905e.
31. M. Fox, Optical Properties of Solids, Oxford, 2nd Ed., United Kingdom: Oxford University Press, 2010.
32. Z. Zhang, H. Chen, Z. Lin, X. Guan, J. Zhang, X. Tang, Y. Zhan, J. Luo, “Pivotal role of the granularity uniformity of the WO₃ film electrode upon the cyclic stability during cation insertion/extraction”, Nanomaterials, 13(6), 973, 2023. https://doi.org/10.3390/nano13060973.
33. K. Ç. Demir, “Corrosion behavior of electrodeposited WO₃ thin films”, Ceramics International, 46(4), 4358–4364, 2020. https://doi.org/10.1016/j.ceramint.2019.10.159.
34. G. Leftheriotis, P. Yianoulis, “Development of electrodeposited WO₃ films with modified surface morphology and improved electrochromic properties”, Solid State Ionics, 179(38), 2192–2197, 2008. https://doi.org/10.1016/j.ssi.2008.07.018.
35. W. L. Kwong, N. Savvides, C. C. Sorrell, “Electrodeposited nanostructured WO₃ thin films for photoelectrochemical applications”, Electrochimica Acta, 75, 371–380, 2012. https://doi.org/10.1016/j.electacta.2012.05.019.
36. G. Mineo, F. Ruffino, S. Mirabella, E. Bruno, “Investigation of WO₃ electrodeposition leading to nanostructured thin films”, Nanomaterials, 10(8), 1493, 2020. https://doi.org/10.3390/nano10081493.
37. W. L. Kwong, H. Qiu, A. Nakaruk, P. Koshy, C. C. Sorrell, “Photoelectrochemical properties of WO₃ thin films prepared by electrodeposition”, Energy Procedia, 34, 617–626, 2013. https://doi.org/10.1016/j.egypro.2013.06.793.
38. H. D. Zheng, J. Z. Ou, M. S. Strano, R. B. Kaner, A. Mitchell, K. Kalantar-Zadeh, “Nanostructured tungsten oxide—properties, synthesis, and applications”, Advanced Functional Materials, 21(12), 2175–2196, 2011. https://doi.org/10.1002/adfm.201002477.
39. J. Liu, G. Zhang, K. Guo, D. Guo, M. Shi, H. Ning, T. Qiu, J. Chen, X. Fu, R. Yao, J. Peng, “Effect of the ammonium tungsten precursor solution with the modification of glycerol on wide band gap WO₃ thin film and its electrochromic properties”, Micromachines, 11(3), 311, 2020. https://doi.org/10.3390/mi11030311.