Fourier transform infrared photothermal spectroscopic characterization of Prussian blue surface modified electrodes. Countercation effects
Fourier transform infrared photothermal spectroscopy was used in conjunction with cyclic voltammetry to characterize graphite electrodes which were surface modified by the deposition of an iron-containing plasma polymer or iron-containing plasma deposit followed by the electrochemical deposition of iron hexacyanoferrate. These results support the formation of surface-bound Prussian brown, Berlin green, Prussian blue, and Everitt's salt depending on the potential of the electrode and the identity of the cation of the bulk electrolyte. The electrode-surface-bound iron hexacyanoferrate acts as a zeolite in which hydrated K+ and Na+ may enter into the lattice. Hydrated Li+, which possesses a larger hydration shell, cannot enter the countercation sites associated with the low-spin iron redox couple and, having entered those sites associated with the high-spin iron redox couple, is unable to exit. The naked or unsolvated cations K+, Na+, or Li+ can enter these countercation lattice sites when the solvent is propylene carbonate. Results presented here suggest that the countercation lattice sites associated with the high-spin Fe(3+/2+) redox couple are distinguishable from the countercation cavities associated with the low-spin Fe(III/II) redox couple. © 1985 American Chemical Society.
