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.