Electrocatalytic Conversion of Plasma-Activated CO2 Toward Multicarbon Products

Abstract

Renewable electricity-powered CO2 reduction reaction (CO2RR) toward chemicals and fuels has been gaining significant attention not only for achieving net-zero carbon emissions but also for enabling long-term energy storage. In electrochemical conversion, CO2 can be upgraded into single- or multicarbon products such as carbon monoxide, formate, and ethylene with remarkable selectivity. However, challenges still exist in terms of high overpotential, limited product range, and low production rates. Moreover, most reported CO2RR to multicarbon products which used Cu as catalysts have predominantly generated C2 products like ethylene or ethanol. However these systems require further performance improvement to target C3+ products which have higher energy density and market price. Another electrified conversion technique involves non-thermal plasma, which can activate CO2 into radical, ionized, and vibrationally excited species at atmospheric pressure and near-ambient temperature. However, plasma processes are non-selective, which poses limitations for controlling reaction pathways and necessitates H2 or light alkanes as co-reactants to produce hydrocarbons.We synergized plasma and electrocatalytic conversion to demonstrate a combined CO2RR process that overcomes the limitations of each individual method. Through the integration of a dielectric barrier discharge plasma and an electrochemical flow reactor, pre-activated CO2 was electrochemically converted on a Cu electrode to produce multicarbon products. The combination enhanced the faradaic efficiency and reaction rate of desirable products and opened new reaction pathways by increasing the activity of CO2 prior to adsorption. The production rates of ethanol, propanol, and acetaldehyde were significantly increased, and new products such as methanol, acetylene, and ethane that were formed only in the combined reaction were detected. The product distribution was studied according to plasma-activated states of CO2 and the electrochemical applied potential. To elucidate the synergistic effects in the combined system, the selectivity and production rates were compared with those in the plasma-only and electrochemical-only reactions. Further control experiments using ground-state reactants were conducted, and the excited states during plasma activation were identified by optical electron spectroscopy. This work represents not only electrocatalysis of pre-activated reactants for enhanced generation of multicarbon products during electrified conversion of CO2, but also demonstrates synergistic convergence of plasma and electrocatalysis for converting reactants possessing strong chemical bonds.