Triggering the Dual-Metal-Site Lattice Oxygen Mechanism with In Situ-Generated Mn3+ Sites for Enhanced Acidic Oxygen Evolution

The development of high-performance non-Ir/Ru catalysts for the oxygen evolution reaction (OER) in acid is critical for the applications of proton exchange membrane water electrolyzers (PEMWEs). Here, we report a new kind of heterostructure catalyst by loading 5.8% Ag nanoparticles on MnO nanorods (Ag/MnO) for acidic OER. The as-prepared Ag/MnO requires only an overpotential of 196 mV for the OER at a current density of 10 mA cm^–2 in 0.5 M H₂SO₄ and operates in a PEMWE for over 300 h at a current density of 200 mA cm^–2, representing one of the best non-Ir/Ru OER catalysts. Operando X-ray absorption spectroscopy confirms that the introduction of trace Ag can promote the generation of highly active Mn³⁺–O sites with oxygen vacancies at a low voltage, leading to a dual-metal-site lattice oxygen-mediated pathway with faster kinetics than the adsorbate evolution mechanism. Theoretical calculations indicate that the trace Ag promotes the overlap between the d orbitals of Mn and the s, p orbitals of O, thereby activating the lattice oxygen and reducing the OER energy barrier. The dissolution of Mn is also suppressed by Ag due to the increased energy for vacancy formation of Mn, where the stability number reaches a high value of 3058, supporting improved structural stability.