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

Abstract

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 FE_HCOOH > 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/Bi^δ+ 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.