Modulating D-Band Electron Occupancy in Ru-Based Heterostructures for Durable Acidic Oxygen Evolution.

The rational design of acid-stable, iridium-free electrocatalysts for the oxygen evolution reaction (OER) is critical for advancing proton exchange membrane water electrolysis (PEMWE), yet balancing activity and durability remains a formidable challenge. Herein, we report a RuO2/Mn3O4 heterojunction with engineered oxygen vacancies (Ov) as a durable, high-performance iridium alternative. Engineering triggers substantial electron transfer from Mn3O4 to RuO2, lowering the average Ru oxidation state from +3.69 to +3.34 and increasing d-band occupancy from 4.23 to 4.50. This enhanced occupancy strengthens Ru-O covalency via intensified coupling with O 2p orbitals, corroborated by density functional theory calculations showing a reduced energy barrier of potential-determining step by 0.62 eV. In situ spectroscopy further reveals a distinctive dual H2O adsorption configuration at adjacent Ru-Ov sites, enabling direct O-O coupling and promoting a more efficient OER pathway. Consequently, the optimized RuO2/Mn3O4-Ov catalyst achieves an exceptionally low overpotential of 185 mV at 10 mA cm- 2 and a turnover frequency of 4.33 s- 1 at 185 mV-188-fold higher than commercial RuO2. Notably, it maintains stable operation for over 200 h at 100 mA cm- 2 in 0.1 M HClO4, highlighting its promise for replacing iridium catalysts in PEMWE applications.