Polymer Ligands with Quaternary Ammonium Binding Motifs on Metal Nanoparticles Enable Selective Ion Transport for CO ₂ Electroreduction

Abstract We report a new class of hydrophobic polymer ligands with quaternary ammonium head groups for surface modification of noble metal nanoparticles (NPs). Quaternary ammonium ligands bind NPs through non‐covalent electrostatic interactions, producing polymer‐grafted NPs with high colloidal and chemical stability. These polymers having charged head groups offer powerful strategies to tailor the structure and function of metal‐electrolyte interfaces in electrocatalytic systems. The ammonium head groups serve as ionic reservoirs that preconcentrate bicarbonate counterions at the surface of nanocatalysts, while the hydrophobic polymer backbones restructure local hydrogen‐bonding networks, modulating water and ion transport dynamics. These interfacial effects promote CO 2 electroreduction, particularly under diffusion‐limited conditions, resulting in a CO Faradaic efficiency (FE) exceeding 90%.