Ligand Recognition Directs Functional Ionic Layer Construction on Metal Nanoclusters for Electrocatalysis

Abstract Cation effects are central to electrocatalytic CO2 reduction, but freely dissolved cations lack positional control, defined function and persistent coupling to surface motifs. Precise regulation of such ionic microenvironments remains difficult in ligand-stabilized metal nanocatalysts, where interfacial modification often perturbs ligand organization and metal core structure. Here we use atomically precise [Au25(EBA)18]− nanoclusters (EBA = 4-ethynylbenzoic acid) as model electrocatalysts to develop a ligand-recognition strategy for constructing interfacial ionic layers. Phenylbiguanide (PGd) was selected as a bifunctional cation: its phenyl motif enables recognition-driven association with the aromatic EBA ligand shell through CH−π interactions, whereas its biguanidinium unit offers NH2 and NH sites for CO2 binding and activation. This design positions PGd beyond the first ligand shell as a site-proximal ionic promoter, forming a defined ionic layer while preserving access to active sites. Constrained ab initio molecular dynamics calculations indicate that protonated PGd maintains hydrogen-bond coupling with CO2, facilitating CO2 capture and activation near Au sites. Molecular analyses resolve PGd association, binding range and interfacial configuration. Optimized PGd incorporation lowers the overpotential by 200 mV and achieves a FECO of 95.6% at −0.7 V during CO2 reduction. These results establish ligand recognition as a route for converting diffuse cation effects into defined ionic microenvironments on atomically precise electrocatalysts.