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

Öz

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.

Anahtar Kelimeler

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

Proje Numarası

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

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

Öz

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.

Anahtar Kelimeler

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

Destekleyen Kurum

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

Proje Numarası

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

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