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 (FE_CH4 = 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 FE_CH4 to 78.5 ± 0.4% at -1.3 V for Cu₁₅/CeO₂ and 64.3 ± 1.9% at -1.4 V for Cu₁₈/CeO₂. <i>In situ</i> XAS and <i>ex situ</i> 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.