Study on isothermal thermochemical CO2 splitting: CALPHAD for thermodynamic analysis of spinel FeAl2O4

The isothermal thermochemical redox cycle shows promise for solar fuel production due to its benefits in reactor design and hat recovery. While previous studies have examined benchmark material CeO2 for isothermal water or carbon dioxide decomposition, its high reduction temperature and relatively low energy conversion efficiency have limited its practical applicability. This study conducts a thermodynamic analysis of FeAl2O4 in a solar thermochemical two-step cyclic CO2 splitting system. The Computational Phase Diagram (CALPHAD) thermodynamic calculation method is utilized to assess the cyclic CO yield of isothermal cycles. The findings suggest that optimizing the oxygen partial pressure during reduction significantly boosts CO yield, with yields of 445 μmol/g, 827 μmol/g, and 1083 μmol/g observed at 10−4 bar, 10−5 bar, and 10−6 bar, respectively. Additionally, the study investigates the influence of heat recovery on solar-to-fuel conversion efficiency. Under isothermal cycle at 1350 °C, the system efficiency reached a peak of 6.12 % at 10−5 bar. After adopting an 80 % heat recovery strategy, it increased to 9.19 %. Sensitivity analyses highlight the critical impact of parameters such as cycle temperature and the heat recovery coefficient on efficiency. This research provides valuable insights into the fuel yield and conversion efficiency in isothermal solar thermochemical cycles.