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 dete rmination of oxidation state profiles in nickel hexacyanoferrate derivatize d electrodes under potential control in an electrochemical cell. Line-imagi ng 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 de rivatization of nickel electrodes. The cyanide stretching region of the Ram an spectrum of the film is shown to be sensitive to iron oxidation state an d is modeled by both univariate and multivariate correlations. Although bot h correlations fit the calibration set well, the multivariate (principle co mponent regression or PCR) model's predictions of oxidation state are less sensitive to noise in the spectrum, yielding a much smoother oxidation stat e 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 sit u oxidation stare profiles indicate that the 647.1 nm laser illumination ph oto-oxidizes the derivatized electrodes. This observation is confirmed usin g photoelectrochemical methods. (C) 1999 The Electrochemical Society. S0013 -4651(97)05-063-5. All rights reserved.