The electrochemical performance of Cu23 NC was thoroughly evaluated across a range of constant voltages, specifically from -0.6 to -1.4 V vs. the reversible hydrogen electrode (RHE). This evaluation was conducted using CO2saturated 0.1 M KHCO3 aqueous solution as the electrolyte within a gas-flow H-type cell setup. Following the electrochemical testing, an in-depth analysis was performed utilizing gas chromatography (GC) and 1 H NMR to characterize the gas and liquid products, respectively. Our results indicated that hydrogen (H2), carbon monoxide (CO), and formic acid (HCOOH) were the products generated during the CO2RR (Figure and Figure ). To verify that these products originated from the flowing CO2, a control experiment was carried out using constantpotential electrolysis in an argon (Ar) atmosphere instead of CO2. The absence of CO2RR products at all tested potentials in the Ar atmosphere confirmed that the detected products were indeed derived from CO2 and not from any other source (Figure ). The Faradaic efficiency (FE) data demonstrated a significant increase in total efficiency with increasing potential, rising from 8% at -0.6 V to 74% at -1.4 V (Figure ). Initially, at -0.6 V, no CO2RR products were obtained. The formation of HCOOH and a small amount of CO was first observed at -0.8 V. As the potential became more negative (from -1.0 V to -1.4 V), the selectivity for HCOOH increased significantly, reaching saturation (FEHCOOH ~26%) at -1.2 V, where hydrogen evolution reaction (HER) was nearly at constant. Beyond -1.2 V, the formation of CO is increasing with the increasing potential where the HER and FEHCOOH are almost constant. To evaluate the stability of the material under the applied electrochemical conditions, we identified the constant current densities at each voltage for one hour duration (Figure ). Chronoamperometric measurements were then conducted at -1.0 V for a period of 6 hours to determine the material's practical applicability (Figure ). Notably, the current density remained stable over this extended period, showing no discernible degradation. Following this prolonged electrochemical catalysis, we further assessed the stability of the Cu₂₃ NCs outside the electrochemical environment after electrocatalysis. TEM image confirmed the structural integrity of the NCs, evidenced by the consistent size of the individual clusters (Figure ). However, the Cu K-edge XANES spectra revealed a significant change in spectral features in respect to the before catalysis, however the electronic structure still maintains the Cu(I) environment from the similar peak top ~8994 eV (Figure ). The shift in FT-EXAFS spectra for changing Cu-S or P bond clarifies such drastic shift in the XANES spectrum which is might be attributed to the ligand desorption (Figure ). We assume that some of the PPh3 ligands were removed during the prolonged electrochemical conditions, which change the Cu-S or P bond strength but due to the neutral nature of the PPh3 ligand the overall electronic structure of the cluster remain same. Fourier-transform infrared (FT-IR) analysis of the Cu23 NCs before and after catalysis supports this assumption. The FT-IR spectra displayed the intense O=P stretching frequency after catalysis sample, indicates the desorption of the PPh3 units from the cluster (Figure ). Thus, this desorption occurs during the electrochemical process, leading to some current loss, which prevents the overall FE from reaching its optimal level.