Electrochemical Oxygen Pump Assisted Solar Thermochemical CO2 Reduction

Abstract Maintaining low oxygen partial pressure during ceria reduction is critical for efficient solar thermochemical fuel production, yet conventional routes rely on energy-intensive gas sweeping or vacuum pumping. We demonstrate a ceria-based reactor operated with a hybrid oxygen removal strategy; moderate sweep gas coupled with electrochemical oxygen pumping (SG + EOP), that enables in situ oxygen removal with reduced auxiliary energy. Increasing EOP’s operating potential from 0.5 to 1.0 V at moderate argon flow increased the molar oxygen production rate during reduction and led to a 15.6% increase in overall solar to fuel efficiency (from 0.307% to 0.355%). At these conditions, the EOP accounted for up to 12.1% of the total oxygen removal. Durable performance was demonstrated for over 102 redox cycles when controlled cooldown was ensured to prevent interfacial delamination. When scaling up to 500 kW, the lowest CO price was projected to be 1.19 $·kg -1 at the highest annual output (2.33 × 10 4 kg·year -1 ) for SG + EOP compared to the SG and SG + VP (vacuum pump) method, establishing this hybrid approach as a practical and scalable pathway toward efficient and solar-to-fuel systems.