Selective formaldehyde condensation on phosphorus-rich copper catalyst to produce liquid C3+ chemicals in electrocatalytic CO2 reduction

Recent advancements in the CO2 reduction reaction (CO2RR) target multicarbon chemical production and scalable electrode designs for industrial applications. Here we introduce a zero-gap cell utilizing humidified gas-phase CO2 and circulated alkaline media, achieving a Faradaic efficiency of 66.9% for C3+ products and a current density of −1,100 mA cm−2. In situ spectroscopic analyses revealed formaldehyde as a key intermediate formed on copper oxide/hydroxide interfaces derived from a phosphorus-rich copper catalyst. Unlike conventional pathways based on dimerization of CO intermediates, our study selectively produces liquid-phase multicarbon products because of autonomous local pH variations under a weak alkaline microenvironment, with allyl alcohol as the dominant C3+ product. The high selectivity and efficiency for liquid products provide a substantial advantage for storage and transport, highlighting the scalability and practical feasibility of our approach, which offers a potential economically viable solution for CO2 utilization. This development encourages the adoption of CO2RR technologies in iron–steel and petrochemical industries to mitigate greenhouse gas emissions. Electrocatalytic CO2 reduction has largely been limited to C1 and C2 products, especially at high current densities. Here, a Faradaic efficiency of 67% is reported for C3+ products from CO2 at 1.1 A cm−2 via a formaldehyde condensation mechanism on a phosphorus-rich copper catalyst.