Easily constructed porous silver films for efficient catalytic CO2 reduction and Zn–CO2 batteries

Abstract

For the electroreduction of carbon dioxide into high value-added chemicals, highly active and selective catalysts are crucial, and metallic silver is one of the most intriguing candidate materials available at a reasonable cost. Herein, through a novel two-step operation of Ag paste/SBA-15 coating and HF etching, porous silver films on a commercial carbon paper with a waterproofer (p-Ag/CP) could be easily fabricated on a large scale as highly efficient carbon dioxide reduction reaction (CO₂RR) electrocatalysts with a CO Faraday efficiency (FE_CO) as high as 96.7% at −1.0 V vs. the reversible hydrogen electrode (RHE), and it still reaches up to 90% FE_CO over applied potentials ranging from −0.8 to −1.1 V vs. the RHE. Meanwhile, the membrane electrode assembly (MEA) utilizing the p-Ag/CP catalyst has achieved a current density, FE_CO, and stability of ∼60 mA cm⁻², >91%, and 11 h, respectively. Furthermore, the assembled aqueous Zn–CO₂ battery using p-Ag/CP cathode yielded a peak power density of 0.34 mW cm⁻², 75 charge–discharge cycles for 25 h, and 64% FE_CO at 2.5 mA cm⁻². Compared with flat Ag/CP, the significant enhancement in the CO₂RR activity of p-Ag/CP was mainly attributed to the distinctive porous structure and an improved three-phase boundary, which is capable of inducing the stabilization of *COOH intermediates, increased active specific surface areas, fast electron transfer kinetic and mass transportation. Further, theoretical calculations revealed that p-Ag/CP possessed an optimized energy barrier for *COOH intermediates.