Visualization of the\nDistance-Dependent Synergistic\nInteraction in Heterogeneous Dual-Site Catalysis

Understanding\nthe characteristics of interfacial hydroxyl\n(OH)\nat the solid/liquid electrochemical interface is crucial for deciphering\nsynergistic catalysis. However, it remains challenging to elucidate\nthe influences of spatial distance between interfacial OH and neighboring\nreactants on reaction kinetics at the atomic level. Herein, we visualize\nthe distance-dependent synergistic interaction in heterogeneous dual-site\ncatalysis by using ex-situ infrared nanospectroscopy and in situ infrared\nspectroscopy techniques. These spectroscopic techniques achieve direct\nidentification of the spatial distribution of synergistic species\nand reveal that OH facilitates the reactant deprotonation process\ndepending on site distances in dual-site catalysts. Via modulating\nIr–Co pair distances, we find that the dynamic equilibrium\nbetween generation and consumption of OH accounts for high-efficiency\nsynergism at the optimized distance of 7.9 Å. At farther or shorter\ndistances, spatial inaccessibility and resistance of OH with intermediates\nlead to OH accumulation, thereby diminishing the synergistic effect.\nHence, a volcano-shaped curve has been established between the spatial\ndistance and mass activity using formic acid oxidation as the probe\nreaction. This notion could also be extended to oxophilic metals,\nlike Ir–Ru pairs, where volcano curves and dynamic equilibrium\nfurther evidence the universal significance of spatial distances.