Study on isothermal thermochemical CO2 splitting: Structural reaction of spinel FeAl2O4 foam ceramics

The isothermal thermochemical redox cycle is a promising route for solar-driven CO 2 splitting, as it enables stable heat input and simplifies reactor design. However, achieving high redox activity and long-term stability remains a challenge for oxygen carrier materials. In this study, spinel FeAl 2 O 4 foam ceramics were synthesized at three calcination temperatures for 1300 °C (FA-13), 1400 °C (FA-14), and 1500 °C (FA-15), to investigate the redox performance. X-ray diffraction patterns were tested and confirmed that FA-14 and FA-15 both exhibited a pure FeAl 2 O 4 phase, while FA-13 retained residual Al 2 O 3 . The structure characteristics and scanning electron microscopy analyses revealed that FA-14 exhibited optimal porosity (74.41 %) and uniform grain distribution. In contrast, FA-15 showed densification and reduced porosity (71.75 %), while FA-13 displayed structural defects and poor crystallinity. Isothermal CO 2 splitting tests at 1400 °C demonstrated that FA-14 achieved the highest CO yield of 206 μmol/g, outperforming CeO 2 , FA-13 and FA-15. Long-term cycling tests over 50-cycle redox test(>100 h) showed that FA-14 maintained stable CO and O 2 yields of 170 ± 10 μmol/g and 97 ± 5 μmol/g, respectively indicating excellent thermal stability under high-temperature operation condition. These results demonstrate that tuning the calcination temperature of FeAl 2 O 4 ceramics can optimize their redox performance by balancing crystallinity and porosity.