(380q) Robust Perovskite Oxygen Sorbent Particles for “Low Temperature” Thermochemical Air Separation
As a potentially more efficient alternative to cryogenic air separation, thermochemical air separation via cyclic redox reactions of an oxide-based oxygen sorbent has been extensively investigated recently. Although a number of promising oxygen sorbents have been proposed and investigated, further improvements in sorbent performance through fundamental understanding of the relationships between oxygen sorbentsâ structural/compositional properties and redox performance are highly desirable.
In this study, we systematically investigated the effects of A and B site dopants on the oxygen uptake/release properties of SrFeO3 family of perovskites as oxygen sorbents. Addition of dopants to the A site, namely Ba and La, or the B site, Cu or Mn, increased the oxygen capacity for temperature and pressure swings when compared to undoped SrFeO3 with the best sample showing an increase of oxygen capacity of 0.16%. Based on these results, the Mn sample underwent 1000 redox cycles where the sorbent was subjected to oxygen partial pressure swings between 20% O2 and inert at 600 °C. In this scheme, the material was oxidized for 4 minutes, and reduced for 6 minutes. The sample proved to be stable in terms of oxygen storage capacity, with less than a 3% decrease in capacity. The redox kinetics were similar for the last few cycles when compared to the first few cycles. DFT calculations, in conjunction with the experimental results, indicated that oxygen vacancy formation energies are correlated to initial decomposition temperature for the samples investigated. However, the oxygen storage capacities of the doped samples did not show good correlation with the vacancy formation energies. It was further determined that the dynamic nature of the redox process makes it difficult to use a single vacancy formation energy as the descriptor for the oxygen storage capacities of the sorbents. Instead, a systematic approach was developed to correlate the oxygen storage capacities with the sorbentsâ compositional properties and vacancy formation energies. The findings from this study can potentially be used to develop improved sorbents for thermochemical air separation.