High-yield electrochemical upgrading of CO2 into CH4 using large-area protonic ceramic electrolysis cells

Electrochemical production of commodity chemicals via CO2–H2O co-electrolysis using solid oxide electrolysis cells presents a promising cost-effective energy-storage approach. Here, we harness the unique property of protonic ceramic electrolysis cells (PCEC) and demonstrate direct electrochemical production of CH4 from CO2–H2O in a PCEC unit-cell stack. An exceptional CH4-yield ratio of 34.6% from only CO2–H2O reactants and greater than 70% with exhaust H2 recycle were achieved under an electrolysis current of –1 A cm–2 at 450 °C. Additionally, the electrochemical co-conversion of CO2–H2O offered a higher CH4-yield ratio compared to the thermochemical conversion of CO2–H2 under certain operating conditions, indicating possible electrochemical promotion of catalytic CO2 methanation. Techno-economic analyses were conducted to reveal potential operating conditions that yield a promising levelized cost of fuel production. The demonstrated good performance of the unit-cell stack shows promising scalability of PCECs for practical application from a system-level viewpoint.