Electrochemical impedance spectroscopy to study photo - induced effects on self-organized TiO2 nanotube arrays

• Published in: Electrochimica acta Vol. 55; no. 20; pp. 5938 - 5946
• Main Authors: PU, P, CACHET, H, SUTTER, E. M. M
• Format: Journal Article
• Language: English
• Published: Kidlington Elsevier 01.08.2010
• Subjects: Chemical Sciences; Chemistry; Electrochemistry; Exact sciences and technology; General and physical chemistry; Photoelectrochemistry. Electrochemiluminescence; Titanium IV Oxides; Scanning electron microscopy; Electrochemicalimpedance spectroscopy; Nanotube; Sodium Sulfates; Photoinduced effect; Transition metal; Anodization; Surface states; Surface structure; Ultraviolet radiation; Self organization; Nanotubular structure; Anodizing; Morphology; Compact layer; Titanium; Raman spectrometry; Titanium dioxide; Electrochemical impedance spectroscopy; Titanium dioxide; Anodization; Nanotubular structure; Compact layer; Electrochemical impedance spectroscopy; Surface states
• ISSN: 0013-4686; 1873-3859
• DOI: 10.1016/j.electacta.2010.05.048

Two different morphologies of nano-structured titanium dioxide–a nanotubular layer and a compact layer - were obtained by anodization of titanium in fluoride-based baths, and the photo-induced effects of these layers were investigated by electrochemical impedance spectroscopy (EIS). The first layer showed long–lasting photo-induced modifications after UV illumination, whereas, in the case of the compact layer, no long-lasting UV-induced modifications were observed. Before light exposure, in the nanotubular layer, only the bottom of the tubes were electro-active and contributed to the conduction of the layer. Moreover an exponential distribution of surface states could be evidenced. After UV exposure, the surface states were filled by the photo-generated electrons, leading to activation of the walls of the tubes by inserted hydrogen, and to a hundred fold increase in the space charge layer capacitance. This capacitance increase was attributed to an increase in the active surface of the layer, but also to an increase in the charge carrier density.