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

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 CO₂ electroreduction, particularly under diffusion-limited conditions, resulting in a CO Faradaic efficiency (FE) exceeding 90%.