Electrocatalytic reduction of CO2 by a complex of rhenium in thin polymeric films

The electrochemical properties of thin polymeric films on electrodes prepared by reductive electropolymerization of fac-[(vbpy)Re1(CO)3L]n+ (L = Cl− or CH3CN; n = 0 or 1, respectively; vbpy = 4-methyl-4'-vinyl-2,2'-bipyridine) and coelectropolymerization of these with cis-[(bpy)2Ru(vpy)2]2+ (vpy = 4-Vinylpyridine) have been investigated in the presence of CO2. The metal sites in the thin films show a dramatic increase in reactivity and stability toward CO2 reduction, particularly in the copolymeric assembly, as compared to the homogeneous analog, fac-[(vbpy)Re)CO)3Cl] in solution. As with the monomer, the major CO2 reduction product is CO but a bimolecular carbon-carbon coupling pathway to form oxalate appears for the pure poly-[(vbpy)Re(CO)3Cl] film. The results of electrochemical kinetic studies on poly-[(vbpy)Re(CO)3Cl] show that the rate determining step in the films changes from the chemical reaction between reduced Re and CO2 to electron transport to the catalytic sites as the film thickness is increased.