PM IRRAS spectroelectrochemistry of layer-by-layer

TAGLIAZUCCHI, MARIO E.; MENDEZ DE LEO, LUCILA PAULA; CALVO, ERNESTO J.

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Congreso; Electrocatalysis, Present and Future; 2011

In situ polarization modulation infrared reflection absorption spectroscopy (PMIRRAS) has been used to study layer-by-layer self-assembled films made of a novel redox polymer bearing an osmium pentacyano pyridine complex (PAH-OsCN) and polyacrylic acid at different electrode potentials and solution compositions.[1]   For the system PAH-OsCN/PAA, PMIRRAS provides direct information on the oxidation state of the pentacyano redox couple, the fraction of protonated carboxylates, the content of counterions and the film hydratation as a function of electrode potential and bulk solution composition. The novel redox polymer synthesized in this work allowed us to follow the oxidation state of the film.   This work demonstrates the simultaneous determination of the oxidation state and counterion content of an LbL film. Comparison of the potential evolution of the NO3 IR peak and the CN–Os(III) stretching band provided a spectroscopic, chemically specific proof of previous experimental observations. We proposed that nitrate is accumulated in the film mainly due to the incorporation of cations. This mechanism implies a loss of permselectivity probably due to the rupture of intrinsic polycation–polyanion pairs.   An interesting finding of the present work is that while approximately two thirds of the redox sites are electrically connected to the electrode and follow the Nernst relationship, the rest are electrochemically isolated and can only be oxidized/reduced by chemical agents in solution.   We also present spectroscopic evidence that nitrate ions enter into the film during oxidation and leave during reduction. The number of these anions involved in the first process is larger than that participating in the latter and hence nitrate accumulates within the film.   References [1].    Tagliazucchi, M.; Méndez De Leo, L. P.; Cadranel, A.; Baraldo, L. M.; Völker, E.; Bonazzola, C.; Calvo, E. J.; Zamlynny, V., “PM IRRAS spectroelectrochemistry of layer-by-layer self-assembled polyelectrolyte multilayers”, Journal of Electroanalytical Chemistry 2010, 649, (1-2), 110-118.