Electrolyte Flow-Driven Coupling of Oxygen Evolution Reaction and CO₂ Electroreduction for Promoting Selective HCOOH Production under Acidic Conditions

The electrocatalytic CO2 reduction reaction (ECO2RR) toward liquid fuels is one of the most promising routes to sustainable carbon neutrality. However, reducing energy consumption and improving product selectivity of the ECO2RR in acidic environments remain challenging. To address these issues, we propose a novel process by coupling the oxygen evolution reaction (OER) and ECO2RR using an anode-to-cathode electrolyte flow to enhance formic acid (HCOOH) production under acidic conditions. The coupling process achieves an outstanding Faradaic efficiency (FE) of 95.9% for HCOOH production, reduces cathodic energy consumption by 19.5% compared with the traditional ECO2RR, and exhibits superior stability with FEHCOOH > 80% for over 80 h at 200 mA cm–2. Dissolved oxygen is activated on the Bi-Bi2O2CO3@CNTs cathode to produce *OOH, lowering the activation energy barrier of CO2 and facilitating the formation of key intermediates (*OCHO) for HCOOH production. Furthermore, the coupling process can modulate the local interfacial electric field to promote the activation of CO2 in the acidic electrolyte. Dissolved oxygen facilitates the Bi/Biδ+ redox cycle to provide active sites for the conversion of CO2 to HCOOH during long-term electrolysis. This study provides a proof-of-concept demonstration of the ECO2RR/OER coupling process, making CO2 electroreduction more energy-efficient and economical.