Constructing multiphase manganese oxide/perovskite Heterostructures via acid etching modulated A-site nonstoichiometric lanthanum manganite for the oxygen reduction reaction

Developing efficient and economical non-precious metal catalysts for the oxygen reduction reaction (ORR) is critical for clean energy technologies. Herein, we report a highly effective synergistic strategy for constructing manganese oxide/LaMnO₃ perovskite heterojunctions by combining A-site defects with acid etching to realize the high-performance manganese-based ORR catalysts. The strategy involves synthesizing a thermodynamically metastable, A-site-deficient La_0.5MnO_3-α precursor to pre-activate the perovskite lattice. A subsequent mild acid etching triggers a deep structural reconstruction and an in-situ phase transition, forming a hierarchical nanocomposite of residual perovskite and nanocrystalline MnO_x. This two-step process enables precise manipulation of the electronic structure, A-site deficiency initially creates a high Mn⁴⁺ state, which is then tuned back to an optimal Mn⁴⁺/Mn³⁺ ratio via electron compensation from acid-induced oxygen vacancies. The resulting catalyst, La_0.5MnO_3-α - 3, possesses a vast specific surface area (109.2 m² g^-1), abundant surface defects, and an optimized electronic structure. Consequently, it exhibits outstanding ORR performance in alkaline media, with a high half-wave potential (0.65 V vs. RHE), a high limiting current density (4.6 mA cm^-2), a low Tafel slope (115 mV dec^-1), and near-ideal 4-electron selectivity (n = 3.99). This work establishes a new design paradigm for advanced electrocatalysts through function-oriented material reconstruction.