The development of non-platinum group metal (non-PGM) and efficient multifunctional electrocatalysts for oxygen reduction reaction (ORR), oxygen evolution reaction (OER), and hydrogen evolution reaction (HER) with high activity and stability remains a great challenge. Herein, by in-situ transforming silver manganese composite oxide heterointerface into boosted Mott–Schottky heterointerface through a facile carbon reduction strategy, a nanorod-like silver/manganese oxide with superior multifunctional catalytic activities for ORR, OER and HER and stability was obtained. The nanorod-like silver/manganese oxide with Mott–Schottky heterointerface (designated as Ag/Mn₃O₄) exhibits an ORR half-wave potential of 0.831 V (vs. RHE) in 0.1 M KOH, an OER overpotential of 338 mV and a HER overpotential of 177 mV at the current density of 10 mA·cm⁻² in 1 M KOH, contributing to its noble-metal benchmarks comparable performance in aqueous aluminum-air (Al-air) battery and laboratorial overall water splitting electrolytic cell. Moreover, in-situ electrochemical Raman and synchrotron radiation spectroscopic measurements were conducted to further illustrate the catalytic mechanism of Ag/Mn₃O₄ Mott–Schottky heterointerface towards various electrocatalytic reactions. At the heterointerface, the Ag phase serves as the electron donor and the active phase for ORR and HER, while the Mn₃O₄ phase serves as the electron acceptor and the active phase for OER, respectively. This work deepens the understanding of the Mott–Schottky effect on electrocatalysis and fills in the gap in fundamental physical principles that are behind measured electrocatalytic activity, which offers substantial implications for the rational design of cost-effective multifunctional electrocatalysts with Mott–Schottky effect.