Spectroelectrochemistry of palladium hexacyanoferrate films on platinum substrates

Among the Prussian blue analogs, palladium hexacyanoferrate (PdHCF) is of interest from electrochromic and catalytic perspectives, but has not been extensively studied to date. In this paper we report on the combined use of cyclic voltammetry and in situ infrared and UV–vis spectroelectrochemistry of PdHCF films potentiodynamically grown on platinum electrodes. Infrared spectroscopy (in the cyanide stretching frequency region) showed two pairs of interrelated bands at 2075 cm−1/2180 cm−1 and 2110 cm−1/2130 cm−1. UV–vis reflectance spectroscopy also showed two distinct sets of features that are entirely in agreement with the voltammetric peaks and infrared signatures at corresponding potentials. These redox processes have excellent stability and correspond to two PdHCF compound stoichiometries bearing Pd/Fe elemental ratios of 1:1 and 3:2, respectively. A comparison of redox processes and compound stoichiometries in PdHCF with counterparts of Group VIII B metals (namely Ni and Pt) is finally presented.