Non-directly bonded single-atom pairs towards H2/CO electrooxidation

Single-atom catalysts (SACs) challenge conventional multi-site catalysis by enabling oxidative processes like H2 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. 18O 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 H2 oxidation. While H2O 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.