Hole-Mediated Lattice Oxygen Redox Design for Perovskite Oxide Catalysts

Abstract

Present design and application of perovskite oxide catalysts assume lattice oxygen redox (LOR) mechanisms that depend on lattice oxygen activity without consideration of the entire redox cycle. Herein, using in situ characterizations and theoretical calculations, we uncover a hole-mediated LOR cycle on p-type Sr-deficient SrFeO_3–δ (SFO-Srv) perovskites in CO oxidation reaction. Sr vacancies activate surface lattice oxygen of SFO-Srv and promote formation of highly covalent Fe^(4–x)+-O^(2–x)– sites. In situ electrical conductivity measurement demonstrates that holes directly participate in the entire LOR cycle, and are reversibly consumed and regenerated in reducing/oxidizing atmosphere via Fe^(4–x)+-O^(2–x)– sites of SFO-Srv. Hole-mediated LOR in SFO-Srv, as revealed by in situ soft X-ray absorption spectroscopy, occurs through changing in covalency of Fe−O bonds, O 2p hole state, and electron density of Fe sites. ¹⁸O₂ labeling experiment further confirms an improved Mars–van Krevelen pathway in the hole-mediated LOR cycle, which accounts for a ten-times enhancement of SFO-Srv for CO reaction rate over that of SFO alone.