Enabling Realistic Flue Gas Electroreduction to Formate on BiOI Gas Diffusion Electrode via Tandem Electrochemical Strategies

Electrochemical CO2 reduction (CO2RR) offers a promising approach for upcycling CO2 into high-value chemicals within the broader framework of carbon capture and utilization technologies. However, the overall process remains economically challenging due to high operating and infrastructure costs, particularly when carbon capture units are required to purify real emission sources such as industrial flue gas. In this work, we investigate flue gas electroreduction to formate using hydrothermally derived BiOI gas diffusion electrodes as a model high-performance Bi-based catalyst. Under pure CO2, the BiOI electrodes exhibit exceptionally high Faradaic efficiency (98%) and excellent stability, sustaining operation for 60 h at 300 mA cm–2. Under simulated flue gas feeds containing CO2, N2, O2, NO, and SO2, however, performance was limited by two competing effects: CO2 mass-transport limitations at high current densities and parasitic oxygen reduction at low current densities. To address these challenges, we developed tandem electrochemical strategies that independently regulate the reaction microenvironment and gas composition. Pulsed electrolysis mitigated CO2 depletion and increased the formate FE from 34 to 61% at 100 mA cm–2 under a dilute CO2 feed (15% CO2/85% N2). In parallel, an upstream electrochemical O2-removal step enabled CO2RR by suppressing parasitic oxygen reduction. To the best of our knowledge, this represents the first fully electrochemical system for direct conversion of simulated flue gas to formate. By combining O2 removal with pulsed electrolysis, simulated flue gas containing 15% CO2, 5% O2, 150 ppm NO, and 100 ppm SO2 (balance N2) was converted to formate with an FE of 51%. These results demonstrate that flue gas electroreduction can be enabled through fully electrochemical management of gas-phase impurities and interfacial mass transport.