Monolithic Cl-Modified Nanoporous Ag Nanowires for Electrochemical CO₂ Reduction to CO

Nanoporous catalysts with large surface areas are promising electrocatalysts to reduce carbon dioxide (CO2). However, previous methods of producing nanoporous catalysts require a high temperature (>500 °C) or a long processing time (∼12 h). Herein, we develop a facile method to produce monolithic nanoporous Ag nanowires (NWs) within a few minutes. The Cl2 plasma treatment on a Ag-coated plastic film induces the rapid growth of vertically aligned AgCl NWs due to the highly reactive Cl radicals and strain-relaxation-driven growth of NWs. Then, AgCl NWs are electrochemically reduced to produce nanoporous Ag NWs with a high electrochemical surface area. Moreover, the residual Cl– anions on the surface of the nanoporous Ag NWs increase CO2 reduction activity. Consequently, the Ag NWs have a 90 times higher electrochemical surface area but less than 0.06 times as much charge-transfer resistance as the Ag film. As a result, the Ag NWs achieve a high selectivity of CO (FECO = 98.7%) and high CO partial current density of 3.16 mA/cm2 at −0.8 VRHE, which is 20 times higher than that of Ag foil (0.16 mA/cm2). Moreover, the Ag NWs had a good long-term stability even after 60 h of CO2 reduction.