Crystallinity-controlled oxygen vacancies of SmMn2O5 as an oxygen reduction catalyst for Zn-air battery

Abstract

Mn-based mullite, with its unique structure featuring two distinct Mn coordination environments, has garnered significant attention in the research and development of oxygen reduction reaction (ORR) catalysts. The nucleation and growth of SmMn₂O₅ were influenced by controlling the hydrothermal reaction time and temperature, resulting in SmMn₂O₅ with varying degrees of crystallinity. With the increase of hydrothermal temperature and time, the crystallinity of SmMn₂O₅ is enhanced, and the morphology changes from an amorphous lamellar structure to a finer and longer nanorod structure. SmMn₂O₅ with an amorphous lamellar structure prepared at 150 °C for 3 h has a maximum specific surface area of 355.35 m² g⁻¹. The electrochemical results indicate that the amorphous lamellar SmMn₂O₅ shows excellent ORR performance with a half-wave potential of 0.76 V. This is mainly due to the fact that crystallinity induces an increase in the number of oxygen vacancies, which increases the number of active sites and changes the valence state of Mn. The amorphous lamellar SmMn₂O₅ was used as a cathode in zinc-air batteries with a power density of 119 mW/cm², showing potential applications. This work demonstrates an effective and simple strategy for increasing the number of oxygen vacancies in SmMn₂O₅, which helps the development and application of SmMn₂O₅ in the field of electrocatalysis.