PM IRRAS spectroelectrochemistry of layer-by-layer self assembled polyelectrolyte multilayers

MARIO TAGLIAZUCCHI; LUCILA P. MÉNDEZ DE LEO; ALEJANDRO CADRANEL; LUIS M. BARALDO; CECILIA BONAZZOLA; ERNESTO J. CALVO; VLAD ZAMLYNNY

JOURNAL OF ELECTROANALYTICAL CHEMISTRY

ELSEVIER

Año: 2010

0022-0728

In-situ PM IRRAS was used to study layer by layer films made of a novel redox polymer bearing an osmium pentacyano pyridine complex (PAH-OsCN) and polyacrylic acid for different electrode potentials and solution compositions. PM IRRAS reports on the oxidation state of the osmium complex, the protonation fraction of carboxylates and the content of IR-active counterions (nitrate anions) and water (hydratation of the multilayer). It advantages differential techniques used in the past to study redox polyelectrolyte multilayers (i.e. SNIFTIRS) because it measures the absolute IR-signal arising from the molecular species in the interface, rather than their variation with respect to a reference state. For instance, we show that only a fraction of the total number of redox sites responds to changes in the electrode potential as predicted by the Nernst equation. The remaining sites are trapped in the Os(II) or Os(III) states and can only be oxidized/reduced by chemical agents in solution. We also present spectroscopic evidence that nitrate ions enter 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 thus nitrate accumulates within the film. This finding is analyzed in terms of two possible mechanisms.