The significant stabilization of the *HCOO intermediate on Cu11PTT NC arises from its optimized active sites and its core atomic framework. Conversely, Cu18PTT NC demonstrates a stronger preference for competitive side reaction than Cu11PTT NC. This is evidenced by its lower energy barrier for H adsorption, which competes directly with CO2RR intermediates. To further validate these findings, d-band center energy calculations were performed, which indicate higher reactivity for Cu11PTT NC over Cu18PTT NC (Figure ). The d-band center analysis reveals that Cu11PTT NC has a d-band center closer to the Fermi level, exhibiting stronger interaction with CO2RR intermediates compared to Cu18PTT NC. These differences in reactivity and selectivity, despite both NCs sharing similar thiolate ligands on their surfaces, underscore the pivotal role of structural architecture in dictating product distribution and efficiency for both CO2RR and the competitive HER.