Electrochemical redox processes at cobalt hexacyanoferrate modified electrodes: An in situ Raman spectroelectrochemical study

• Redox state of cobalt hexacyanoferrate layer at electrode can be estimated by Raman spectroscopy.
• Redox processes within this layer are limited by intrinsic electron transfer rate.
• Electroreduction of hydrogen peroxide is limited by slow redox transformations within the modifier layer.

Cobalt hexacyanoferrate (CoHCF) modified electrode has been prepared by electrodeposition, and studied by cyclic voltammetry and Raman spectroscopy using near-infrared laser excitation (785 nm). Raman features observed within the spectral range of 2200–2000 cm−1, related to tripple C–N bond vibrations, have been analysed. Based on in situ spectroelectrochemical study performed in potassium or sodium chloride or nitrate electrolytes, Raman bands located around 2130 and 2080 cm−1 have been assigned to reduced, and the band around 2185 cm−1 – to oxidised form of CoHCF. With the use of time-resolved Raman spectroelectrochemistry, it has been shown that the electrochemically driven redox interconversion between the two redox forms of CoHCF proceeds relatively slow, in contrast to fast transformations occuring within Prussian blue layers studied previously. It was also shown that the efficiency of some electrode processes taking place at CoHCF modified electrode, like the cathodic reduction of hydrogen peroxide, appears to be limited by slow redox transformations within the modifier layer.