Voltammetric and Electrochemical Impedance Spectroscopy Study of Prussian Blue/Polyamidoamine Dendrimer Films on Optically Transparent Electrodes

Abstract

Electrochromic Prussian Blue (PB) films were prepared on clean and dendrimer modified optically transparent electrodes (OTE). As expected, surface attached polyamidoamine (PAMAM) dendrimers, modified not only the chemical structure but also the electric properties of the interphase and therefore, exerted a clear influence on the electrochromic behavior of the PB films. The electrochromic efficiency of the modified substrate for instance, was clearly dependent on the size (Generation, G) of the surface confined dendrimer molecule, and the effects on this and other properties of the electrode could be associated to ion transport of charge compensating species (K + , Cl − ) as well as effects on electrochemical charge transfer (resistance to the electronic transfer) of the electrochromic films. Using Electrochemical Impedance Spectroscopy (EIS) experiments of the dendrimer modified interphases under study, fitted values of the electric components of an equivalent circuit were obtained and used to gain understanding of the dendrimer induced effects of the electrochromic response of PB films. This study is expected to contribute to the understanding of this type of interphases so that the design and construction of electrochromic films in which ionic as well as electronic transport, can be properly tailored and employed. Prussian Blue (PB) is a coordination compound characterized by electrochromic, photosensitive and electrocatalytic properties 1-4 that have allowed its use for the development of sensors, 5-6 energy storage technologies, 7 corrosion inhibitors, 8 dyes 9 and electrochromic devices. [10][11] In the case of electrochromic devices, polymeric redox active films characterized by a reversible color change due to an oxidation/reduction process caused by the imposition of an electric current are deposited on the surface of transparent conductive electrodes. Therefore, the construction of efficient electrochromic materials is an area of current research, and in this context, PB containing films have been prepared employing polymeric matrixes such as polyaniline, 12 Nafion, 13 poly(3-methylthiophene) 14 and PAMAM dendrimers (DMs). 15,16 In this regard, PAMAM hyper-ramified dendritic materials are particularly interesting due to their molecular architecture, which significantly improves the physical and chemical properties of the composite when compared to traditional linear polymers. 15,16 In this work, the study of the influence of PAMAM DMs of different generations on the electrochemical properties of PB films is presented. The results show that only the DMs of lower generation (G0.5) have the capability of increasing the electrochromic efficiency of PB films when compared to surfaces constructed in the absence and in the presence of higher generation DMs. The water employed in all the experiments reported in this work was purified with a Milli-Q system reaching a resistivity higher than * Electrochemical Society Member.z E-mail: lgodinez@cideteq.mx 18 M · cm −1 . N 2 (4.8 grade) was bubbled for 15 min before...

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