Non-directly bonded single-atom pairs towards H(2)/CO electrooxidation.

Single-atom catalysts (SACs) challenge conventional multi-site catalysis by enabling oxidative processes like H and CO oxidation. However, we herein present that the completely isolated SACs are inactive, while spatially adjacent single-atom pairs (interatomic distance < 4 Å) work cooperatively as the true active sites. Rh atomic densities were precisely tuned between 0.1 wt%-17.5 wt% via graphene quantum dots confinement. Mathematical modeling quantifies the scaling of active pairs versus electrochemical performance, rationalizing activity dependence on atomic proximity. O isotope labeling and in situ synchrotron infrared spectroscopy analyses identified a new reaction mechanism, with water bifunctional dissociation enabled on sub-4 Å Rh pairs, and acts as the rate-determining step towards both CO and H oxidation. While HO enters the COOR process as a reactant and enters the HOR process as a molecular catalyst. Our findings redefine bifunctional catalysis, merging single-atom precision with nanoparticle-like cooperativity for efficient energy conversion systems.