Polyoxometalate-Promoted Electrocatalytic CO2 Reduction at Nanostructured Silver in Dimethylformamide.

Electrochemical reduction of CO2 is a promising method to convert CO2 into fuels or useful chemicals, such as carbon monoxide (CO), hydrocarbons, and alcohols. In this study, nanostructured Ag was obtained by electrodeposition of Ag in the presence of a Keggin type polyoxometalate, [PMo12O40]3- (PMo). Metallic Ag is formed upon reduction of Ag+. Adsorption of PMo on the surface of the newly formed Ag lowers its surface energy thus stabilizes the nanostructure. The electrocatalytic performance of this Ag-PMo nanocomposite for CO2 reduction was evaluated in a CO2 saturated dimethylformamide medium containing 0.1 M [ n-Bu4N]PF6 and 0.5% (v/v) added H2O. The results show that this Ag-PMo nanocomposite can catalyze the reduction of CO2 to CO with an onset potential of -1.70 V versus Fc0/+, which is only 0.29 V more negative than the estimated reversible potential (-1.41 V) for this process and 0.70 V more positive than that on bulk Ag metal. High faradaic efficiencies of about 90% were obtained over a wide range of applied potentials. A Tafel slope of 60 mV dec-1 suggests that rapid formation of *CO2•- is followed by the rate-determining protonation step. This is consistent with the voltammetric data which suggest that the reduced PMo interacts strongly with CO2 (and presumably CO2•-) and hence promotes the formation of CO2•-.