Significance of Engineering the MnO₆ Octahedral Units to Promote the Oxygen Reduction Reaction of Perovskite Oxides.

Abstract

The electronic structure and geometric configuration of catalysts play a crucial role to design novel perovskite-type catalysts for oxygen reduction reaction (ORR). Nowadays, many studies are more concerned with the influence of electronic structure and ignore the geometric effect, which plays a nonnegligible role in enhancing catalytic performances. Herein, this work regulates the MnO₆ octahedral tilting degree of LaMnO₃ by modulating the concentration of Y³⁺, excluding the electronic effect from the valence state of manganese. Plotting the MnO₆ octahedral tilting degree as a function of concentration of Y³⁺ produces a volcano-shaped plot. The octahedral tilting can reduce the Mn-O covalency, generating more highly active Mn³⁺ and oxygen vacancies during ORR process. The specific activity has a positive correlation with octahedral tilting degree. Meanwhile, the octahedral tilting stabilizes Mn-O interactions during ORR process and promote stability. Based on experimental results and DFT calculations, octahedral tilting alters the rate-determining step (RDS) and decrease the energy barrier. Subsequent extended experiment confirms that octahedral tilting is the key factor to affect the catalytic performances.