Plasmonic Gold Antenna–Copper Molecular Complex Reactor Assembly for Exclusive CO ₂ to Formate Conversion under White-Light Irradiation

Achieving high product selectivity in photoelectrochemical CO₂ reduction remains a persistent challenge for molecular electrocatalyst platforms. Herein, we present a plasmonic-molecular hybrid catalyst, AuTNP@Cu(PAP)₂, comprising a redox-active copper complex, [Cu(PAP)₂], immobilized onto gold triangular nanoprisms (AuTNPs) through noncovalent interactions. The intimate coupling between the plasmonic antenna and the molecular catalytic sites enables highly selective photoelectrochemical CO₂-to-formate conversion, achieving a Faradaic efficiency (FE) of ∼95% and a formate yield of 468.3 μmol·cm⁻² within 4 h at -0.56 V vs RHE. The hybrid electrode exhibits remarkable durability, maintaining an average formate production rate of ∼350 μmol·h⁻¹·cm⁻² and 91% FE over 25 h of continuous operation in an H-Cell. Mechanistic investigations combining ultrafast transient absorption spectroscopy, in situ Raman analysis, and density functional theory (DFT) calculations reveal that the Au-Cu interfacial interaction promotes plasmon-induced hot-electron transfer, stabilizes the surface-bound *OCHO intermediate, and extends charge-separated lifetimes, which are key factors governing the observed formate selectivity. Integration of the hybrid electrode into a custom-built photoelectrochemical flow reactor demonstrated scalability, delivering an FE of 90% at 50 mA·cm⁻² under white-light illumination. This study establishes a unified design principle for constructing robust plasmon-driven molecular architectures that achieve high selectivity, efficiency, and durability in the CO₂ conversion reactions.