Pr6O11: Temperature-Dependent Oxygen Vacancy Regulation and Catalytic Performance for Lithium-Oxygen Batteries.

Abstract

Many challenges still exist in lithium-oxygen batteries (LOBs), particularly exploring an efficient catalyst to optimize the reaction pathway and regulate the Li2O2 nucleation. Pr6O11 has a unique 4f electronic structure and the highest oxygen ion mobility among rare earth oxides, exhibiting superior electronic, optical, and chemical properties. These unique properties might endow it with advanced catalytic activities for LOBs. This work reports two crystal forms of Pr6O11 as novel catalysts and regulates the oxygen vacancy (Vo) concentrations by feasible calcination. Thermogravimetric analysis, X-ray diffraction, and X-ray photoelectron spectroscopy (XPS) confirm the conversion from commercial Pr6O11 to cubic fluorite Pr6O11 and Vo-rich Pr6O11. Photographs, high-resolution transmission electron microscopy, selected area electron diffraction, XPS, and electron paramagnetic resonance robustly demonstrate the temperature-dependent evolution of Vo. Ex situ XPS, scanning electron microscopy, and electrochemical techniques are used to study the catalytic mechanism and electrochemical reversibility. It is found that an appropriate Vo concentration can boost O2 adsorption/desorption, accelerate electron transport, and reduce the reaction energy barrier. Vo-rich Pr6O11 optimizes the reaction pathway by offering an intermediate Li2-xO2 (with metalloid conductivity) and adjusting Li2O2 into vertically staggered nanoflakes, effectively avoiding the suffocation of the catalytic surface and presenting excellent capacity, cycling stability, and rate performance.