The electrochemical reduction of CO2 in a highly selective and efficient manner is a crucial step toward its reuse for the production of chemicals and fuels. Nanostructured Ag catalysts have been found to be effective candidates for the conversion of CO2-to-CO. However, the ambiguous determination of the intrinsic CO2 activity and the maximization of the density of exposed active sites have greatly limited the use of Ag toward the realization of practical electrocatalytic devices. Here, we report a superstructure design strategy prepared by the self-assembly of two-dimensional Ag nanoprisms for maximizing the exposure of active edge ribs. The vertically stacked Ag nanoprisms allow the exposure of >95% of the edge sites, resulting in an enhanced selectivity and activity toward the production of CO from CO2 with an overpotential of 152 mV. The Ag superstructures also demonstrate a selectivity of over 90% for 100 h together with a current retention of ≈94% at -600 mV versus the reversible hydrogen electrode and a partial energy efficiency for CO production of 70.5%. Our electrochemical measurements on individual Ag nanoprisms with various edge-to-basal plane ratios and the Ag superstructures led to the identification of the edge ribs as the active sites thanks to the ≈400 mV decrease in the onset potential compared to that of the Ag (111) basal planes and a turnover frequency of 9.2 × 10-3 ± 1.9 × 10-3 s-1 at 0 V overpotential.
Keywords: CO2 reduction reaction; electrocatalysis; self-assembly; silver; two-dimensional materials.