Electrochemical behavior of Ag + intercalated layered oxides Ugur Unal * , Shintaro Ida, Kenji Shimogawa, Ozge Altuntasoglu, Kazuyoshi Izawa, Chikako Ogata, Taishi Inoue, Yasumichi Matsumoto Department of Nano Science and Technology, Faculty of Engineering, Kumamoto University, Kurokami 2-39-1, Kumamoto 860-8555, Japan Received 14 October 2005; received in revised form 13 May 2006; accepted 19 July 2006 Available online 28 August 2006 Abstract Electrochemical reaction of Ag + in the interlayer of various layered oxides was investigated in this study. Intercalation of Ag + into the interlayer of layered oxides was carried out with layer-by-layer self assembly (LBL) method. Film deposition with LBL method was mon- itored by UV–vis spectra. Ag + intercalated layered oxide films showed very unique characteristics when compared to other similar Ag + exchanged zeolite and clay electrodes. First of all, the peaks are very sharp and clear, which shows that the redox reaction in the inter- layer is fast. In addition, there is an energy gap between the onset potentials of redox reactions, which is different from the behavior of other electrodes. The formation of the energy gap was assigned to the energy barrier in the host layer. Furthermore, pH and scan rate controlled experiments showed that the reaction has diffusion controlled mechanism and diffusion of H + or K + into interlayer is believed to be contributing to the redox reaction indirectly. The slope of I p versus m 1/2 curves shows that redox reaction is reversible. The unique electrochemical behavior of the Ag + intercalated layered oxide thin films may lead into the design of new nanocells using the potential energy difference between two different redox couple. Ó 2006 Elsevier B.V. All rights reserved. Keywords: Silver; Intercalation; Layered oxides; Cyclic voltammogram; Electrochemistry 1. Introduction Layered oxides are promising materials in many fields with their two-dimensional structure. Their ability of easy modification makes them available in various application areas, such as photocatalysis [1–3], photoelectrochemistry [4–6], and photoluminescence [7–11]. For instance, the superconducting properties of Cu [12,13] and Co [14] lay- ered oxides are brought about mainly from the host oxide layer with a planar structure. As a photocatalysis in water splitting process, interlayer of layered oxides acts as a site for the oxidation of water by holes produced in the semi- conductive host nanosheet layer under band gap illumina- tion [15–18]. Recently, some interesting electrochemical properties of Ti and Nb layered oxides such as n-type semi- conducting behavior of the host nanosheet layer with pho- toelectrochemical response [4,5], clear electrochemical redox reaction of the Ag + /Ag couple and visible light response of the RuðbpyÞ 2þ 3 in the interlayer to yield a signif- icant amount of photocurrent [6,19] have been revealed in our laboratory. These electrochemical reactions are based on the unique two-dimensional structure of these types of layered oxides in principle. Layered materials have been used for battery applica- tions because of their unique layered structures [20–24]. The intercalative feature of these materials is benefited in order to produce an electrical energy. For example, electro- chemical intercalation for the positive electrode in the Li- cell is a well-known behavior for layered oxides with both properties of high electrical conductivity of the host nano- sheet layer and high ionic conductivity of the guest cation in the interlayer [25]. Charge–discharge sequence in these kinds of batteries is based on the intercalation–deintercala- tion cycle between two intercalation compounds forming the negative and positive poles of a battery cell. 0022-0728/$ - see front matter Ó 2006 Elsevier B.V. All rights reserved. doi:10.1016/j.jelechem.2006.07.021 * Corresponding author. Tel.: +81 96 342 3659; fax: +81 96 342 3679. E-mail address: ugurunal@chem.kumamoto-u.ac.jp (U. Unal). www.elsevier.com/locate/jelechem Journal of Electroanalytical Chemistry 595 (2006) 95–102 Journal of Electroanalytical Chemistry