Thermodynamic Analysis of Isothermal CO2 Splitting and CO2-H2O Co-Splitting for Solar Fuel Production

Abstract Isothermal solar thermochemistry is a promising approach for deriving solar fuels from concentrated solar energy with potential advantages in reactor design and heat recovery. Previous work has demonstrated the feasibility of isothermal water splitting with ceria, but the solar-to-fuel efficiencies and operating temperature range are relatively undesirable. In this study, thermodynamic analysis is performed on the isothermal solar thermochemical splitting of CO 2 as well as co-splitting of CO 2 and H 2 O. The cycling reactions are found to exhibit considerably higher solar-to-fuel efficiencies than that of H 2 O due to the favorable Gibbs free energy change in the CO 2 splitting reaction at elevated temperatures and the lower thermal energy requirement for gas heating due to the lack of phase change in CO 2 . Through the comparison of the conventional two-temperature cycling strategy, the advantages and disadvantages of both methodologies, as well as indications on system and reactor design, are discussed. Strategies for controlling the composition of solar-syngas derived from isothermal co-splitting of CO 2 and H 2 O mixtures are also proposed.