Unveiling the Spatially Dependent Cooperative Effect in Iridium Sites for Enhanced Acidic Water Oxidation

The spatial distance between active sites is a critical factor governing hydroxyl (*OH)-group-mediated synergies in multiphase electrocatalysis. But direct experimental evidence correlating atomic-scale spatial arrangement with synergistic behavior, reaction kinetics, and catalytic mechanisms remains scarce. Using the acidic oxygen evolution reaction (OER) as a model, this study employs in situ synchrotron radiation infrared spectroscopy to demonstrate that adjacent active sites enable direct *OH coupling, forming the *O-O* intermediate. Complementary in situ X-ray absorption spectroscopy and theoretical calculations reveal that adjacent Ir sites induce electronic restructuring. This optimized electronic configuration facilitates unlocking a dual-site synergistic mechanism. Conversely, isolated sites (at a farther distance) exhibit spatial inaccessibility of *OH intermediates, forcing a higher-energy pathway via *OOH formation. These findings establish a universal paradigm for manipulating interfacial *OH dynamics through atomic-scale spatial engineering, applicable to diverse reactions including hydrogen evolution, oxygen reduction, and CO2 reduction.