Collective Behavior of Single-Atom Catalysts: A Synergistic Effect between Strain and Site Configuration.

Fe single-atom catalysts on N-doped graphene (Fe-NC) exhibit good and variable catalytic activity linked to the active site density and configuration. Here, we comprehensively investigate the Fe-NC catalysts under various strained states and site densities to address the interplay between the active site density, local strain, site geometry, and oxygen evolution reaction (OER) activity. It is found that the active site density is closely associated with in-plane strain, which can be tuned by popping up Fe single atoms from the graphene film and, thereby, modulating the OER catalytic activity. Further analysis indicates that there exist three orientations of the FeN 4 active site, each introducing specific anisotropic strain. As a result, the in-plane strain correlates with both the orientation and density of the active site, ultimately influencing catalytic activity. Our findings demonstrate the synergistic effects of multiple factors in single-atom catalysts, providing new insights into the rational design and fine tuning single-atom catalysts via collective interactions.