Ultrahigh Density Ir Single-Atom Catalysts With Synergistic Ir-Ir Pairs for Efficient Acidic Oxygen Evolution

Constructing neighboring active sites in single-atom catalysts (SACs) provides a new strategy for enhancing acidic oxygen evolution reaction (OER) performance. However, the OER activity of such systems is highly sensitive to their structural configuration. Due to the typically low density of single atoms, most synergistic effects originate from interactions between single atoms and the supports, while extensive synergy between neighboring single atoms remains scarce. In this work, we introduced ultrahigh density Ir single atoms onto Co₃O₄ support to construct numerous Ir-Ir pairs for enhanced acidic OER performance. Electrochemical measurements revealed that the SACs achieved an overpotential of only 250 mV at a current density of 10 mA cm^-2, 90 mV lower than that of the lower density SACs, and maintained stability over 3000 h at a current density of 50 mA cm^-2. In a proton exchange membrane water electrolyzer, this catalyst required only 1.69 V to achieve a current densit of 1.0 A cm^-2 and operated stably for 700 h. In situ spectroscopic characterization and density functional theory calculations confirmed Ir-Co pairs in low-density SACs exhibited excessively strong intermediate adsorption, whereas the Ir-Ir pairs formed in ultrahigh density SACs optimized the adsorption strength, thus enhancing the synergistic efficiency of neighboring sites.