Localisation of electrochemical oxidation processes in nickel and cobalt hexacyanoferrates investigated by analysis of the multiplet patterns in X-ray photoelectron spectra

Nickel and cobalt hexacyanoferrate-modified gold electrodes were prepared by electrochemical synthesis. These samples were investigated by X-ray photoelectron spectroscopy (XPS) after removal of the modified electrodes from the electrochemical cell at different potentials and transfer into the ultra high vacuum of the spectrometer. A careful analysis of the multiplet splitting of the 2p photoemission lines of the transition metal ions and comparison with suitable reference compounds and with calculations reveals that the electrochemical oxidation occurs at the iron sites in K2Ni[Fe(CN)6] and at the cobalt sites in the related compound K2Co[Fe(CN)6].