Uncovering the Enhancement Mechanism of the Oxygen Reduction Reaction on Perovskite/Ruddlesden–Popper Oxide Heterostructures (Nd,Sr)CoO₃/(Nd,Sr)₂CoO₄ and (Nd,Sr)CoO₃/(Nd,Sr)₃Co₂O₇

Although the perovskite (Nd,Sr)CoO3 (NSC113)/Ruddlesden-Popper (R-P) oxide (Nd,Sr)2CoO4 (NSC214) heterostructure is reported to improve the oxygen reduction reaction (ORR) activity by 2-3 orders of magnitude, the enhancement mechanism remains unclear. For the first time, we conclude that there are two main factors that can enhance the ORR activity: (1) Oxygen adsorbed on such heterostructures would gain more electrons, promoting the oxygen adsorption. (2) The more distant rock-salt layers on the heterointerfaces can facilitate the insertion of interstitial oxygen and form a high-speed transport channel of interstitial oxygen. Moreover, the perovskite/double-layered R-P oxide heterostructure, which has not been reported yet, is predicted to have better ORR performance than the perovskite/single-layered R-P oxide heterostructure. Our work elucidates the ORR enhancement mechanism on perovskite/R-P oxide heterostructures from the atomic level, which is demonstrated by experiments and, thus, is very meaningful for the development of high-performance electrochemical devices.