Atomically Precise Cu(I) Clusters Facilitated by CeO2-Derived Reverse Hydrogen Spillover for Selective Electrochemical CO2 Methanation

Atomically precise Cu clusters with stabilized low-coordinated Cu+ species demonstrate promising deep CO2 reduction capability, although product selectivity requires enhancement. To address this, two Cu clusters, Cu15(PPh3)6(PET)13(BF4)2 and Cu18S(PPh3)4(PET)16 (denoted as Cu15 and Cu18, respectively) were constructed via ligand-mediated assembly of Cu3 triangular units. Both clusters effectively catalyze deep CO2 reduction, with CH4 as the dominant product (FECH4 = 60.8 ± 1.6% at −1.4 V for Cu15 and 50.5 ± 4.3% at −1.5 V for Cu18). Notably, CeO2 incorporation dramatically enhances CH4 selectivity, elevating FECH4 to 78.5 ± 0.4% at −1.3 V for Cu15/CeO2 and 64.3 ± 1.9% at −1.4 V for Cu18/CeO2. In situ XAS and ex situ XPS analysis validate stabilized Cu+ species within Cu clusters under CO2RR, favoring *CO intermediate stabilization. Kinetic analysis identifies isolated Cu sites within Cu15 clusters as the active center for both CH4 and C2H4 formation, mediating the hydrogenation reaction via the Langmuir–Hinshelwood mechanism while suppressing C–C coupling. Theoretical calculations elucidate that CeO2 facilitates water activation to generate abundant *H species, which subsequently migrate to sulfur sites in Cu15 clusters through a reverse hydrogen spillover mechanism. This synergistic process significantly accelerates *CO hydrogenation kinetics, thereby enhancing the CH4 selectivity.