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Abstract: WO3/chitosan and WO3/chitosan/poly(ethylene oxide) (PEO) films were prepared by the layer-by-layer method. The presence of chitosan enabled PEO to be carried into the self-assembled structure, contributing to an increase in the Li+ diffusion rate. On the basis of the galvanostatic intermittent titration technique (GITT) and the quadratic logistic equation (QLE), a spectroelectrochemical method was used for determination of the “optical” diffusion coefficient (D op), enabling analysis of the Li+ diffusion rate and, consequently, the coloration front rate in these host matrices. The D op values within the WO3/chitosan/PEO film were significantly higher than those within the WO3/chitosan film, mainly for higher values of injected charge. The presence of PEO also ensured larger accessibility to the electroactive sites, in accordance with the method employed here. Hence, this spectroelectrochemical method allowed us to separate the contribution of the diffusion process from the number of accessible electroactive sites in the materials, thereby aiding a better understanding of the useful electrochemical and electrochromic properties of these films for use in electrochromic devices. [Copyright &y& Elsevier]

Abstract: Self-assembled films from SnO2 and polyallylamine (PAH) were deposited on gold via ionic attraction by the layer-by-layer (LbL) method. The modified electrodes were immersed into a H2PtCl6 solution, a current of 100μA was applied, and different electrodeposition times were used. The SnO2/PAH layers served as templates to yield metallic platinum with different particle sizes. The scanning tunnel microscopy images show that the particle size increases as a function of electrodeposition time. The potentiodynamic profile of the electrodes changes as a function of the electrodeposition time in 0.5molL−1 H2SO4, at a sweeping rate of 50mVs−1. Oxygen-like species are formed at less positive potentials for the Pt–SnO2/PAH film in the case of the smallest platinum particles. Electrochemical impedance spectroscopy measurements in acid medium at 0.7V show that the charge transfer resistance normalized by the exposed platinum area is 750 times greater for platinum electrode (300kΩcm2) compared with the Pt–SnO2/PAH film with 1min of electrodeposition (0.4kΩcm2). According to the Langmuir–Hinshelwood bifunctional mechanism, the high degree of coverage with oxygen-like species on the platinum nanoparticles is responsible for the electrocatalytic activity of the Pt–SnO2/PAH concerning ethanol electrooxidation. With these features, this Pt–SnO2/PAH film may be grown on a proton exchange membrane (PEM) in direct ethanol fuel cells (DEFC). [Copyright &y& Elsevier]