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.