Study of the electrochemical reduction of CO2 on a polypyrrole electrode modified by rhenium and copper–rhenium microalloy in methanol media

The electrocatalytic CO2 reduction on rhenium and CuRe alloy highly dispersed on polypyrrole films was studied by means of polarization curves and constant potential electrolysis. The reduction products were analyzed by FTIR and gas chromatography–mass spectrometry. These results were compared with those obtained on these same metals electrodeposited on gold polycrystalline surfaces. In all cases, it was found that after an electrolysis time of 35 h the main reduction products were CO, CH4 and H2. Also, simultaneous mass change measurements using an electrochemical quartz crystal microbalance (EQCM) with cyclic voltammetry and application of step potentials, allow us to postulate that the intermediates generated during the CO2 reduction would be CO or CH2 on Au ∣ Cu and CH2OH or CH2 on Au ∣ CuRe electrodes, respectively. Likewise, the faradaic efficiency obtained for each of these products depends on the substrate nature and on the applied potential. The higher faradaic efficiencies for methane formation were obtained at −1.35 V with Au ∣ PpyRe (34%) and Au ∣ PpyCuRe (31%). In both cases, these efficiencies were independent of the hydrodynamic conditions of the electrolytic solution.