Optimized Oxygen Reduction Reaction of Sm<sub>0.7</sub>La<sub>0.3</sub>Mn<sub>2</sub>O<sub>5</sub> Nanorods by a Lanthanum Dopant for Zinc–Air Batteries
Xiao-ran Wen, Xue-wei Wang, Ke Ma, You-Lin Chen, Chang Yeon Yu, Zhihao Yuan
Abstract
Mullite oxides have been studied for decades as oxygen reduction reaction (ORR) electrocatalysts because of their flexible and tunable electronic structures. In this work, a larger radius La was used to replace Sm to synthesize a series of nanorod-shaped SmxLa1–xMn2O5 catalysts by a two-step hydrothermal method. Compared with SmMn2O5, Sm0.7La0.3Mn2O5 has a higher half-wave potential (0.83 V vs reversible hydrogen electrode), which exhibits excellent ORR electrocatalytic activity in alkaline media. Meanwhile, Sm0.7La0.3Mn2O5 shows better ORR stability, higher electron transfer number, and lower hydrogen peroxide yield. The excellent electrocatalytic activity is mainly owing to that the introduction of La changes the bond length of Mn–O, thereby increasing the amount of Mn3+. The elongated nanorods increase the specific surface area of the sample and exhibit more active sites on the reaction surface. Furthermore, rechargeable zinc–air batteries made of Sm0.7La0.3Mn2O5 not only have a high power density (147.1 mW cm–2), but exhibit excellent cycling stability in long-term charge–discharge tests over 800 h. This work not only provides a series of low-cost and highly active electrochemical catalysts for zinc–air batteries, but also provides a convenient and effective method for the wide and practical application of zinc–air batteries.