We observed that in alkaline conditions (5 M KOH), GDEs could reach -500 mA cm -2 at applied potentials of approximately -0.5 V vs. RHE with no significant differences between the current-voltage responses for Cu and Cu-SPy samples (Fig. , Fig. ). Controlled current electrolysis (CCE) experiments using Cu and Cu-SPy GDEs were conducted at different current densities to see if the molecular species influenced selectivity. Cu-SPy GDEs displayed remarkably high faradaic efficiency (FE) values for HCOO -of (81 ± 4)% at -100 mA cm -2 and (72 ± 2)% at -300 mA cm -2 with a maximal partial current density for formate of 217 ± 5 mA cm -2 and a corresponding cathodic energy efficiency for HCOO -(EE½ HCOO -) of (55 ± 3)% (Fig. , Table ). In contrast, Cu GDEs showed low FEHCOO-values and generated a wide range of products (Fig. , Fig. ). The FEH 2 values were similar for both the bare and modified electrodes, however Cu-SPy displayed significantly lower yields of CO and COderived C2H4, suggesting that the increase in HCOO -generation comes at the expense of CO (Fig. ). At higher current density (-500 mA cm -2 ) the high formate selectivity was partially lost (FEHCOO-= (41 ± 4)% after 1h) and the FECO and FEC 2 H 4 values increased (Fig. ). We observed no clear morphological changes following electrolysis that could be responsible for the alteration (Figs. and), and the same selectivity trends were observed for purely metallic nanoparticles without air exposure (Cu25-SPy), ruling out oxide retention as a possible factor (Table ). To determine if SPy desorption was responsible for the alteration, we tracked its presence in the electrolyte solution using UV-Vis spectroscopy (Note S1). At -300 mA cm -2 (≈ -0.40 V vs. RHE) < 4% desorption was observed after 1 h, and the presence of SPy was confirmed using XPS (Fig. , Table ). However, at -500 mA cm -2 the amount of SPy desorbed from the GDE increased over the course of electrolysis, which correlated well with a drop in HCOO -selectivity, and reached roughly 100% desorption after 2 hat this point the FEHCOO-was comparable to that of bare Cu (Fig. , Table ). The results established that more cathodic potentials (≈ -0.45 V vs. RHE) give rise to reductive desorption but also verified the essential role SPy plays in altering selectivity.