Step-Scan FT-IR Spectroelectrochemical Analysis of Surface and Solution Species in the Ferricyanide/Ferrocyanide Redox Couple

Abstract

Fourier transform infrared (FT-IR) spectrometry adds complementary structural information to sensitive electroanalytical measurements. In this work, in situ, external reflection FT-IR techniques allowed for examination of interfacial electrochemical events through a thin-layer spectroelectrochemical cell in which a sinusoidally modulated potential was applied to the electrode. The infrared spectra of electrochemically modulated species were measured by a step-scan FT-IR spectrometer. The phasesensitive detection capability of this technique has been used to provide information about dynamic electrode processes and to enhance sensitivity to surface species. The cause of decreases in the heterogeneous rate constant, k°, of the ferricyanide/ferrocyanide redox process with time has been investigated. Previous authors offer a variety of opinions for the variation of k°for this reaction including the adsorption of polymeric hexacyanoferrate complexes, ferrocyanide, or ferricyanide on the electrode surface; other reports indicate that no species adsorb on the electrode during the electron-transfer process. Our results indicate that, with KCl as electrolyte, a hexacyanoferrate complex can form during potential cycling in the ferri-/ferrocyanide redox couple, but only under rather extreme experimental parameters. Measurements made by electrochemical modulation combined with step-scan FT-IR spectrometry show that, under other conditions, the change in rate constant of this redox process can be attributed to the adsorption of ferrocyanide ion.

Electrochemical formation of Prussian blue films with a single ferricyanide solution on gold electrode

“…Although there are reports [37,[39][40][41][42] on single ferricyanide solution which indicate formation of PB on the electrode surface, in our preliminary experiments in different salts as supporting electrolyte we did not observe any adsorption. However, adsorption was observed only after potential was cycled over wider potential limits (À0.1 to +0.9 V) than usual (À0.1 to +0.6), i.e., the formation of PB by cyclic voltammetry was obtained in wider potential limits in KCl as supporting electrolyte.…”

“…Under some particular working conditions [36][37][38][39], the FeðCNÞ 3À 6 =FeðCNÞ 4À 6 electron transfer reaction involves the generation of different compounds that often adsorbed on the electrode surface. These species have been identified as Prussian blue or related compounds [37,[39][40][41][42]. Yang et al [36] found that in a weak acidic medium (pH 3.6) of KH 2 PO 4 (0.1 M) -HCl, a thin film of PB is deposited on a gold electrode by using cyclic voltammetry between À0.2 and +0.6 V. They also reported that deposition can occur on platinum and glassy carbon electrodes but the rates were slow (and almost the same) in comparison with those on the gold substrate.…”

Surface-Enhanced Infrared Absorption

“…Unfortunately, the molecular specificity of UVvisible spectroscopy is not high enough. The use of FT-IR spectroscopy has also been examined for this purpose [87,88]. However, the relatively low sensitivity of infrared spectroscopy, the thin-layer structure of the electrochemical cell, and some other technical problems have prevented its practical use.…”

Spatiotemporal Mapping of Diffusion Layers Using Synchrotron Infrared Radiation

“…The infrared signatures of the ferri/ferrocyanide redox couple provide an excellent handle for measuring speciation as the CN stretching vibration blue shifts by $75 cm À1 upon reduction of the iron(III) complex [28][29][30]. Fig.…”