In situ infrared spectroscopic investigations on the electrochemical properties of prussian blue-polyaniline-modified electrodes with various anionic Fe(II) complexes working as a mediator for the electroreduction of CO2

Various Fe(II) complexes have been incorporated into Prussian blue (PB)|polyaniline (PAn)-modified electrodes, and their spectroelectrochemical properties been investigated using in situ and ex situ FTIR methods. It is shown that large anionic complexes once incorporated in the PAn matrix are not dedoped during the potential cycling and the charge balance is maintained by dedoping or incorporating electrolyte cations. This electrode system was applied to the electrocatalytic reduction of CO₂ in aqueous solution, and the reduction products were identified by taking in situ FTIR spectra during the anodic stripping. At potentials higher than 0 V, the IR bands associated with the loss of carboxylic acid at 1362 cm⁻¹ and the gain of CO₂ at 2343 cm⁻¹ were simultaneously observed, indicating that the CO₂ was derived from the reoxidation of carboxylic acid. It is therefore confirmed that CO₂ can be reduced to organic species including carboxylic acid on the PB|PAn-modified electrode with anionic Fe(II) complexes in aqueous solution, with an indication that the existence of the anionic metal complex is essential to such mediated reduction of CO₂.