The sub-nanometer In₂O clusters on Ag nanoparticles with highly selective electrochemical CO₂ reduction to formate

Electrochemical CO₂ reduction (ECR) is a potential route for establishing a carbon–neutral economy. Despite notable breakthroughs, designing a catalytic system with desired product selectivity remains a formidable challenge. Herein, we demonstrate a novel nanoarchitecture comprising sub-nanometer In₂O₃ clusters on Ag nanoparticles (henceforth denoted as Ag₂-In₈/C) for highly selective formate (HCOOH) production in ECR. As-prepared Ag₂-In₈/C NC with the Ag/In atomic ratio of 2/8 achieved the formate faradaic efficiency (FE_HCOOH) of as high as 95.5 % at −0.9 V_RHE with no obvious degradation after 7 h, surpassing the monometallic counterparts (Ag/C and In₂O₃/C) in selectivity and activity. The in-situ X-ray absorption spectroscopy reveals the formation of sub-nanometer In₂O clusters (i.e. Indium changed its phase from In₂O₃ to In₂O) on Ag nanoparticles under potential-driven conditions, where the high activity and selectivity of Ag₂-In₈/C NC originates from the robust synergistic cooperation between Ag and In₂O domains at the Ag-In₂O interface, underscoring its role as the active site for highly selective ECR. Moreover, an amalgamation of the physical and electrochemical analysis suggests that In₂O clusters assist *OCHO formation on the surface of Ag₂-In₈/C NC during ECR and thus pronounced formate selectivity is achieved. In light of our findings, this study promises to unravel intricate mechanistic insights, thus paving the way for the rational design of exceptionally selective catalysts for ECR.