Structural Evolution of Oxide-Derived Nanostructured Silver Electrocatalysts during CO2 Electroreduction

Oxide-derived (OD) metals have been demonstrated as a kind of promising catalyst with superior catalytic activity for carbon dioxide electroreduction. Here we fabricate OD nanoporous silver by a simple, cost-effective electrochemical oxidation–reduction treatment, which enables reducing carbon dioxide to carbon monoxide with a Faradaic efficiency of 87% at −0.8 V vs RHE, significantly higher than that of untreated silver foil under the same conditions. Electron backscattered diffraction analysis reveals that there is a distinct grain refining during the initial CO2 electrochemical reduction from Ag oxide to OD-Ag. Experiment results indicated that the catalytic activity and selectivity are closely linked to the grain boundary and nanoporous structure on the surface, which has also been proven by theoretical calculation. However, after a long catalysis time (12 h), it was found that the surface grain coarsened and the thickness of the nanostructured layer reduced, resulting in the deactivation of the OD-Ag electrode. A dissolution–redeposition mechanism was proposed to govern the degradation of OD-Ag. The catalytic activity can be regenerated again by applying electrochemical oxidation–reduction treatment, which can increase the thickness of the porous layer and electrochemical active surface area significantly.