In situ oxidation state profiling of nickel hexacyanoferrate derivatized electrodes using line-imaging Raman spectroscopy and multivariate calibration

Reported is the use of line-imaging Raman spectroscopy for the in situ determination of oxidation state profiles in nickel hexacyanoferrate derivatized electrodes under potential control in an electrochemical cell. Line-imaging Raman spectroscopy is used to collect 256 contiguous Raman spectra every similar to 5 mu m from thin films (ca. 80 nm) formed by electrochemical derivatization of nickel electrodes. The cyanide stretching region of the Raman spectrum of the film is shown to be sensitive to iron oxidation state and is modeled by both univariate and multivariate correlations. Although both correlations fit the calibration set well, the multivariate (principle component regression or PCR) model's predictions of oxidation state are less sensitive to noise in the spectrum, yielding a much smoother oxidation state profile than the univariate model. Oxidation state profiles with spatial resolution of approximately 5 mu m are shown for a nickel hexacyanoferrate derivatized electrode in reduced, intermediate, and oxidized states. In situ oxidation stare profiles indicate that the 647.1 nm laser illumination photo-oxidizes the derivatized electrodes. This observation is confirmed using photoelectrochemical methods. (C) 1999 The Electrochemical Society. S0013-4651(97)05-063-5. All rights reserved.