Sn-Decorated Cu/Cu 2 O Electrodes Enable Selective CO 2 Reduction to Formic Acid under Realistic Flue Gas Streams

High Resolution Image Download MS PowerPoint Slide The electrochemical reduction of CO 2 is typically investigated under pure CO 2 feeds, but practical deployment must address more complex and dilute sources such as flue gases. Here, we studied Cu/Cu 2 O electrodes decorated with tin (Sn) synthesized using a scalable electrodeposition method and post-treatments under both pure CO 2 and reactive nitrogen oxide-containing simulated flue gas, toward formic acid synthesis. Raman spectroscopy and Atomic Force Microscopy analyses revealed that flue gas exposure induces heterogeneous restructuring of the electrode with surface roughening, surface carbonate formation, and localized redeposition processes. Optimal catalyst performance under pure CO 2 was achieved with intermediate Sn coverage of 3 min electrodeposition, delivering Faradaic efficiencies of 80% and production rates of 370 μmol cm –2 h –1 . Sn-modified Cu 2 O electrodes also exhibited high selectivity toward formic acid under acidic gas containing simulated flue gas, reaching Faradaic efficiencies of 90% albeit at production rates of 113 μmol cm –2 h –1, despite a 10-fold reduced CO 2 partial pressure. These results demonstrate that interfacial Sn–Cu structures enabled selective CO 2 RR even under challenging feed conditions, pointing out both the opportunities and limitations of translating laboratory-scale catalysts to realistic gas streams.