Infrared Spectroelectrochemical Analysis of Adsorbed Hexacyanoferrate Species Formed during Potential Cycling in the Ferrocyanide/Ferricyanide Redox Couple

Abstract

External reflection FT-IR techniques allowed for in situ examination of interfacial electrochemical events occurring in a thin-layer spectroelectrochemical cell. The formation of an adsorbed hexacyanoferrate (HCF) species on a platinum electrode during potential cycling in the ferri-/ferrocyanide redox couple was investigated. At neutral pH with KCl as electrolyte, a hexacyanoferrate complex forms during potential cycling in the ferri-/ferrocyanide redox couple, but only if the potential limits are quite large. Characterization of the adsorbed complex indicates that it initially adsorbs as soluble Prussian Blue (KFeII[FeIII(CN)6]) with no evidence of the presence of insoluble Prussian Blue [Fe4III(Fe2II(CN)6]. This HCF complex can reversibly adsorb and grow on the electrode surface and desorb and decompose to reform solution-phase ferricyanide and ferrocyanide. Adsorption of the HCF complex decreases, but does not completely inhibit, electron transfer.