3 years ago

Low-Temperature Oxygen Storage of CrIV–CrV Mixed-Valence YCr1–xPxO4−δ Driven by Local Condensation around Oxygen-Deficient Orthochromite

Low-Temperature Oxygen Storage of CrIV–CrV Mixed-Valence YCr1–xPxO4−δ Driven by Local Condensation around Oxygen-Deficient Orthochromite
Chunyu Zhu, Chiharu Kura, Satoshi Hinokuma, Aiko Nakao, Kosuke Kuroda, Hiroki Habazaki, Etsushi Tsuji, Yoshitaka Aoki, Makoto Wakeshima, Yukio Hinatsu
The oxygen storage capability and related defect structure of tetrahedral orthochromite(V) compound YCr1–xPxO4 (x = 0, 0.3, 0.5, and 0.7) were investigated by employing thermal gravimetry and in situ X-ray spectroscopy for reversible oxygen store/release driven by heating–cooling cycles in the temperature range from 50 to 600 °C. YCr1–xPxO4 started releasing oxygen as heated from 50 °C under ambient atmosphere, with reduction of CrV to CrIV, while the reduced YCr1–xPxO4−δ phase was significantly reoxidized via absorbing oxygen by cooling to 50 °C under ambient atmosphere, recovering the original stoichiometric phase. Operando X-ray adsorption spectroscopy and first-principles calculations demonstrate that nonstoichiometric YCr1–xPxO4−δ phases were stabilized by forming linking polyhedral CrIV2O76– via corner sharing between oxygen-deficient CrIVO32– and adjacent CrIVO44–. YCr1–xPxO4 was found to have an extremely low reduction enthalpy of about 20 kJ mol–1 probably due to the relatively high reduction potential of high-valence-state Cr(V)/Cr(IV) redox pairs, thereby resulting in reversible oxygen storage in such a low-temperature region.

Publisher URL: http://dx.doi.org/10.1021/jacs.7b05429

DOI: 10.1021/jacs.7b05429

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