Electrostatic Binding of Bicarbonate and Formate in Viologen-Based Redox Polymers: Importance in Catalytic Reduction of Bicarbonate to Formate

The relative importance of electrostatic binding of CO3H- and HCO₂- in a redox polymer derived from an N,.N'-dialkyl-4,4'-bipyridinium monomer has been investigated by Fourier transform infrared (FTIR) spectroscopy. At 298 K and a total concentration of C-containing species of 0.1 M the two species are equally firmly bound in a polymer immobilized on a single-crystal Si electrode surface. When the concentration of C-containing species is 1.0 M, the CO3H- ion is more firmly bound by about a factor of 2.5, and at a total concentration of 3.0 M the CO3H- ion is about 7 times more firmly bound than the HCO2- ion. The HCO2- and C1- anions are equally firmly bound at 1.0 M total anion concentration. On the basis of the lack of change in the cyclic voltammetry response of a derivatized electrode in 1.0 M Na[CO3H] or Na[HCO2] compared to 1.0 M NaCl, the exchange rate of the C-containing anions does not appear to be a factor that would limit the rate of reduction of the CO3H- ion at an electrode modified with the polymer and impregnated with Pd(0).