Copper Doping Boosts Electrocatalytic CO2 Reduction of Atomically Precise Gold Nanoclusters

Unraveling the atomistic synergistic effects of nanoalloys on the electrocatalytic CO₂ reduction reaction (eCO₂RR), especially in the presence of copper, is of paramount importance. However, this endeavor encounters significant challenges due to the lack of the crystallographically determined atomic-level structure of appropriate monometallic and bimetallic analogues. Herein, we report a one-pot synthesis and structure characterization of a AuCu nanoalloy cluster catalyst, [Au₁₅Cu₄(DPPM)₆Cl₄(C≡CR)₁]²⁺ (denoted as Au₁₅Cu₄). Single-crystal X-ray diffraction analysis reveals that Au₁₅Cu₄ comprises two interpenetrating incomplete, centered icosahedra (Au₉Cu₂ and Au₈Cu₃) and is protected by six DPPM, four halide, and one alkynyl ligand. The Au₁₅Cu₄ cluster and its closest monometal structural analogue, [Au₁₈(DPPM)₆Br₄]²⁺ (denoted as Au₁₈), as model systems, enable the elucidation of the atomistic synergistic effects of Au and Cu on eCO₂RR. The results reveal that Au₁₅Cu₄ is an excellent eCO₂RR catalyst in a gas diffusion electrode-based membrane electrode assembly (MEA) cell, exhibiting a high CO Faradaic efficiency (FE_CO) of >90%, and this efficiency is substantially higher than that of the undoped Au₁₈ (FE_CO: 60% at -3.75 V). Au₁₅Cu₄ exhibits an industrial-level CO partial current density of up to -413 mA/cm² at -3.75 V with the gas CO₂-fed MEA, which is 2-fold higher than that of Au₁₈. The density functional theory (DFT) calculations demonstrate that the synergistic effects are induced by Cu doping, where the exposed pair of AuCu dual sites was suggested for launching the eCO₂RR process. Besides, DFT simulations reveal that these special dual sites synergistically coordinate a moderate shift in the d-state, thus enhancing its overall catalytic performance.