Enhanced Solar-to-Fuel Efficiency of Ceria-Based Thermochemical Cycles via Integrated Electrochemical Oxygen Pumping

The solar thermochemical cycle based on ceria is a promising route for renewable fuel production. The solar-to-fuel efficiency of a thermochemical reactor is highly dependent on the oxygen removal during the reduction step. Conventional nitrogen sweeping (NS) requires high heating load and additional gas separation work, which limit the reactor efficiency. We propose the integration of a high-temperature electrochemical oxygen pump (EOP) for in situ oxygen removal to minimize the heating load and to allow for effective oxygen pumping. A transient model was developed to quantify the reactor performance using EOP or NS schemes. The model predicted that the ceria nonstoichiometric coefficient at the end of the reduction was enhanced by 56.8% when using the EOP scheme compared to the NS scheme. Correspondingly, the solar-to-fuel efficiency enhancement factor was 1.64 at reference conditions. In addition, the EOP scheme showed more uniform temperature and species concentration distributions, leading to a more favorable thermo-mechanical stability.