Study of the electrochemical reduction of CO2 on electrodeposited rhenium electrodes in methanol media

The electrochemical reduction of carbon dioxide at a rhenium electrode electrodeposited onto a polycrystalline gold support was studied by means of polarization curves with simultaneous measurement of mass changes by an electrochemical quartz microbalance (ECQM). Potentiostatic electrolysis was done and the analyses of the reduction products were carried out by gas chromatography-mass spectrometry and Fourier transform infrared spectroscopy. The electrolyte was a methanol solution containing 0.1 M LiClO4+CO2, under atmospheric pressure. From the polarization curves it was observed that the CO2 reduction presented a Tafel slope of - 2RT/F, indicating that the first electronation of the CO2 molecule to form the radical anion (CO2.-), is the rate-controlling step. On the other hand, mass change measurements allow us to determine that CO2H and CO correspond to the intermediate species formed during CO2 reduction. The product analysis indicated that the faradaic efficiency for this process depended strongly on the potential at which the electrolysis is carried out and on the hydrodynamic conditions of the solution. Under stirred conditions, the main products were CO (87%) and H-2 (13%) at - 1.35 V. At this same potential and under quiescent conditions, the major products were CO (57%), CH4 (10%) and H-2 (33%). (C) 2001 Elsevier Science B.V. All rights reserved.