Paired Electrosynthesis of Formic Acid from CO2 and Formaldehyde from Methanol

Electrochemical carbon dioxide (CO2) reduction provides a pathway to sustainable chemicals. However, the high electrical energy demand is still a major challenge. Cathodic (CO2) reduction is typically paired with the anodic oxygen evolution reaction (OER), which is energy intensive with limited added value. In this experimental work, we replace OER with partial methanol oxidation to reduce the energy demand while producing formaldehyde and formic acid as value-added chemicals. We investigate methanol oxidation on metallic and oxidized platinum and the paired process with CO2 reduction to formic acid in an electrochemical flow cell. Methanol oxidation on oxidized platinum was more selective to formaldehyde than on metallic platinum but required a higher potential. In the paired process, we achieved a current efficiency for formaldehyde of up to 58% on oxidized platinum at 75 mA cm–2 and 1.8 V vs RHE reaching a concentration of 1.14 mol L–1 formaldehyde. The current efficiency for formaldehyde and formic acid combined reached up to 89%. Methanol oxidation was not affected by pairing, while the current efficiency of CO2 reduction decreased. We report the first production of formaldehyde beyond mechanistic studies by electrochemical methanol oxidation and demonstrate paired CO2 reduction with formaldehyde as primary anodic product.