Net Electronic Charge as an Effective Electronic Descriptor for Oxygen Release and Transport Properties of SrFeO₃-Based Oxygen Sorbents

Abstract

Perovskite oxides, as oxygen sorbents, exhibit excellent potential in thermochemical redox applications such as chemical looping air separation (CLAS), resulting from their excellent redox properties and high tunability. The structural and compositional flexibility of perovskites, while making these mixed oxides highly versatile, also poses challenges for their design and optimization. Moreover, the elevated operating temperature and dynamic oxygen partial pressure swings during redox processes add additional complications for oxygen sorbent design. From a fundamental standpoint, finding simple yet effective descriptors for the effect of cation substitutions on oxygen sorbents’ redox and oxygen transport properties are of significant importance for rational optimization of perovskite-based oxygen sorbents. In the present study, a series of A/B-site-doped SrFeO3‑δ perovskites are investigated using density functional theory (DFT) + U simulations. From these simulations, an effective electronic structural descriptor, the net electronic charge (Δe) of oxygen anions, is extracted based on its excellent correlations with vacancy formation energy, experimentally derived oxygen capacity, and oxygen vacancy migration barrier. These findings provide an effective tool to correlate the oxygen sorbents’ redox performances with a simple yet physically meaningful descriptor for rational design and optimization of perovskites in the context of CLAS.

Chemical Looping Air Separation Using a Perovskite-Based Oxygen Sorbent: System Design and Process Analysis

“…The low reaction enthalpy also supports the potential feasibility of near isothermal operation using packed bed reactors. Such an enthalpy level is also in line with previous experimental and computational studies. ,, …”

“…Such an enthalpy level is also in line with previous experimental and computational studies. 23,24,53 To further determine the thermodynamic driving force required for CLAS operations, kinetic information of the SCFC sorbent was obtained from a TGA. Figure 4 displays the sorbent reaction rates as a function of driving force for the (a) oxidation and (b) reduction reactions of the sorbent.…”

Noble‐Metal‐Assisted Fast Interfacial Oxygen Migration with Topotactic Phase Transition in Perovskite Oxides

“…The basic reactions in energy-conversion process, e.g., oxygen evolution reaction (OER) and oxygen reduction reaction (ORR), usually occur at the interface of oxides, which in turn affect the ion diffusion in bulk materials. The oxygen activity can be tuned by internal factors, such as covalency of metal-oxygen bond, [30] surface reconstruction, [12,31] net electronic charge of O 2− , [32] element doping, [1] etc. As for external factors, the formation of oxygen vacancies can also be induced by gold nanodots decorated on La 0.67 Sr 0.33 MnO 3 surface.…”

High-throughput oxygen chemical potential engineering of perovskite oxides for chemical looping applications

“…First-principles density functional theory (DFT) calculations have shown advantages in computing redox thermodynamics for oxygen carriers. 17,38–41 Recent studies have demonstrated the correspondence between the computed oxygen vacancy formation energies and the experimental P O2 swings. 2,38,39,42,43 To this end, a number of DFT-driven high-throughput studies have been performed: 2,44,45 Lau et al reported an in silico study calculating the theoretical redox equilibria for thousands of oxides and simulated their performance for chemical looping combustion (CLC); 2 Vieten et al calculated the enthalpies for the reduction of 240 perovskites to their brownmillerite phases and proposed an empirical model to pre-select materials for thermochemical water and CO 2 -splitting; 42 Singstock et al applied a DFT-computed descriptor to identify over 1300 promising active materials for CLC and chemical looping sulfur oxidation (CLSO).…”

“…63 Substitution of the A-and/or B-site of SrFeO 3 was shown to be effective toward finetuning its redox properties. 38,39,[64][65][66][67] For instance, A-site doping with La 64 or Ca, 65 B-site doping with Cu 66 or Mn, 67 and A/B-site co-doping with La/Co 68,69 or Ca/Co 53,70 have improved the performance of SrFeO 3 based oxygen carriers for CLAS. These studies confirm that cation substitution can tailor the partial molar enthalpy (DH) and the entropy (DS) for redox reactions.…”