▎ 摘　　要

Multi-Metal Oxide Nanoparticles Multi-metal oxide (MMO) nanomaterials have significant potential to facilitate various demanding (electro)catalytic reactions, but its intrinsic complexity hinders the in-depth understanding of the origin of the catalytic activity. In article number 2110857, Seoin Back, Seung-Ho Yu, Yung-Eun Sung, Taeghwan Hyeon, and co-workers report the structural understanding of uniform-sized spinel-type MMO nanoparticles, which boosts the electrocatalytic oxygen reduction reaction (ORR) activity. Physicochemical and electrochemical analyses reveal the contribution of each element to the structural flexibility and corresponding improved ORR activity.