Inhibiting in Situ Phase Transition in Ruddlesdenpopper Perovskite Via Tailoring Bond Hybridization for Oxygen Ion Conduction

Abstract

Owing to the excellent physical and chemical properties, mixed ionic-electronic conducting (MIEC) oxide materials, especially Ruddlesden-Popper (RP) perovskite oxides with the chemical formula of An+1BnO3n+1, are interesting materials for gas separation, solid oxide fuel/electrolysis cells, polymer electrolyte fuel cells, lithium-ion battery, sodium-ion battery, zinc ion battery and metal-air battery. The in-situ phase transition at different temperatures is a common phenomenon for these MIEC oxide materials, which generally exerts a great influence on the properties and functionalities of these materials and finally determines their performance in various applications. However, the in-depth understanding of the mechanism of phase transitions is still limited so far. Element-doping has been recognized as a facile and efficient strategy to improve the oxygen ionic or electronic conductivity or to stabilize the crystal phase structure (inhibiting both ex-situ and in-situ phase transitions) favorable for oxygen ion conduction. Herein, the ex-situ collapse at room temperature of crystal structure together with the generation of impurities in orthorhombic Pr2NiO4 through Mo doping are observed as the rearrangement of praseodymium atoms-based lattice deformation, which could be attributed to the Mo-induced destabilization of the Pr2NiO4 systems. Noteworthy is that, such effect can be prohibited by controlling the doping contents, and the resultant materials would give rise to the inhibition of in-situ phase transition (high temperature) from low order Pr2NiO4 (An+1BnO3n+1 (n=1)) to high order Pr4Ni3O10 (An+1BnO3n+1 (n=3)) by adjusting bond hybridization at the phase interface. Mo-doping can influence the covalent interaction between praseodymium and oxygen and then promotes the mobility of interstitial oxygen. Pr2Ni1-xMoxO4+ δ were further developed as oxygen separation membrane to help further evaluate the performance of oxygen ion conductivity. In Pr2Ni1-xMoxO4+ δ, Mo doping level of x = 0.05 resulted in an oxygen permeation flux of 3.35 mL min-1 cm-2 at 1000 °C, comparing favorably with the literature. Furthermore, membranes made with Pr2Ni0.95Mo0.05O4+ δ showed high permeation stability in air or helium, and exhibits high CO2 tolerance without obvious decline of the oxygen permeation flux during 500 hours at round 900 °C. This work advances our understanding of the ex-situ and in-situ phase transitions of Pr2NiO4-based RP perovskite materials and shows how Mo doping can stabilizes the in-situ phase structure and improves the mobility of interstitial oxygen. Figure 1