Electrochemical conversion of carbon dioxide into CHO- containing compounds on multimetallic porphyrins

Abstract

This work describes the electrochemical reduction of carbon dioxide in aqueous solution mediated by tetraruthenated metal-loporphyrins (TRP; Co(II) and Zn(II)) in Nafion (Nf) and polyvinyl chloride (PVC) as a support. The comparative aspects of the two polymeric matrices are expressed in terms of the electrocatalytic behavior toward carbon dioxide reduction of both sets of modified electrodes; values of overpotential and turnover frequency were calculated in each case. The modified electrodes under survey were able to reduce carbon dioxide at -600 mV vs Ag/AgCl showing an enhanced reduction current and a decrease in the required overpotential compared to a bare glassy carbon (GC) electrode. Potential-controlled electrolysis experiments were carried out at -1000 mV in order to compare the distribution of products. The production of formic acid, formaldehyde and methanol was confirmed at potentials where reduction of solvent may occur. Measurements of electrochemical impedance spectroscopy show the presence of one active site for GC/Nf/MTRP (where M = Zn(II) and Co(II)) and three for GC/PVC/MTRP. This information corroborates the high values of TOF obtained for GC/PVC/ZnTRP as the best electrocatalyst.