Mechanistic Insights into the Reduction of CO2 on Tin Electrodes using in Situ ATR-IR Spectroscopy

The reduction of CO 2 on tin cathodes was studied using in situ attenuated total reflectance infrared spectroscopy (ATR-IR). Thin films of a mixed Sn/SnO x species were deposited onto a single-crystal ZnSe ATR crystal. Peaks centered at about 1500, 1385, and 1100 cm –1, attributed to a surface-bound monodentate tin carbonate species, were consistently present under conditions at which CO 2 reduction takes place. It was shown that these peaks are only present at potentials where CO 2 reduction is observed. Moreover, these peaks disappear if the pH of the reaction is too low or if the tin surface is chemically etched to remove surface oxide. Sn 6 O 4 (OH) 4 and SnO 2 nanoparticles were shown to be catalytically active for CO 2 reduction, and insights into the oxidation state of the catalytically active species are gained from a comparison of the catalytic behavior of the two nanoparticle species. From these experiments, a mechanism governing the reduction of CO 2 on tin electrodes is proposed.