To assess the electrocatalytic activity of these NCs, we first investigated their CO₂RR capabilities using linear-sweep voltammetry (LSV) in a CO₂-saturated 0.1 M KHCO₃ aqueous electrolyte. The results showed that the Cu11 NCs exhibited the higher reduction currents, followed by the Cu18 NC (Figure ). This initial finding underscores the potential of two Cu11 NCs with distinct ligands for electrocatalytic CO₂RR, even though one shares structural similarities in its ligand framework with the Cu18 NC. The detailed electrochemical performance of these NCs for CO₂RR was evaluated across a range of constant potentials (-0.6 to -1.4 V vs. RHE) using an H-type cell setup. The gaseous products were analyzed using gas chromatography (GC), while liquid-phase products were characterized via 1 H NMR spectroscopy (Figure S11-13). As shown in Figure , the primary products were H2, CO, and HCOOH, but their selectivity was strongly influenced by the structural features of these NCs. To confirm the origin of the CO2RR products and ensure they were derived solely from the CO2 gas source, controlled experiments were conducted under an Ar gas flow in the absence of CO2. Under these conditions, H2 was the only detectable product, providing definitive evidence that the formation of CO and HCOOH observed during CO₂RR is solely attributable to the reduction of flowing CO₂, with no contributions from alternative sources (Figure ). The Faradaic efficiency (FE) analysis of these NCs demonstrated significant variations in the FE values corresponding to the different products formed during the CO2RR (Figure ). These changes in FE were strongly influenced by the specific structural and compositional characteristics of each NC. It has been observed that, Cu₁₁PTT NC selectively produced HCOOH at potentials beyond -0.6 V (vs. RHE), achieving a maximum FEHCOOH of ~45% at -1.2 V (vs. RHE). In contrast, Cu₁₁ABT NCs exhibited HER dominance throughout the potential range (-0.6 V to -1.4 V vs. RHE), with a maximum FEH2 of ~83% at -1.4 V (vs. RHE) (FEH2 of ~82% at -1.2 V vs. RHE). For Cu11ABT, the FEHCOOH was substantially lower, peaking at only of ~5% (FEHCOOH of ~3% at -1.2 V (vs. RHE)) at the same potential. So, despite both NCs having the same number of Cu atoms and nearly identical overall geometries, they displayed stark differences in their electrocatalytic product selectivity and efficiency for CO2RR.