Coupling electrocatalytic CO2 reduction with glucose oxidation for concurrent production of formate with high efficiency

Electrocatalytic reduction of CO2 (CO2ER) coupled with the oxygen evolution reaction (OER) is an energy-intensive process that generates low-value oxygen, limiting its industrial application. To overcome this limitation, here we report a membrane electrode assembly (MEA) system that combines CO2ER with glucose electrooxidation (GEOR) to simultaneously produce formate using bismuth subcarbonate and carbon nanotube hybrid (BOC-CNT) and nickel cobalt oxide decorated on carbon fiber paper (NCO-CFP) as the cathode and anode catalysts, respectively. The BOC-CNT catalyst showed excellent electrocatalytic performance for CO2ER to formate, affording a high FEHCOO- of 97.9 % with current density of 360 mA cm−2 at −0.77 V vs. RHE (-580 mV overpotential), and the NCO-CFP catalyst achieved GEOR at 0.99 V (vs. RHE) with FEHCOO- >98 %. The coupled CO2ER//GEOR MEA exhibits a low onset cell voltage of 1.20 V and reaches ultrahigh apparent Faraday efficiency of formate (>190 %) in a wide range from 1.8 to 2.4 V, achieving ∼ 33.3 % energy savings compared to CO2ER//OER with a high formate yield of 0.92 mol g-1h−1 at 100 mA cm−2. Besides, all generated formate can be collected from the electrolyte on the anode side due to the spontaneous migration of formate under electric field, thus reducing cross-contamination from CO2 and alkaline electrolytes. In addition, the coupled CO2ER//GEOR system exhibited good electrocatalytic stability for at least 32 h. This strategy provides an innovative and promising approach for the co-electrolytic transformation of biomass derivatives and CO2 to formate.