Ligand modification provides a route to improve the stability and reactivity of metal nanoparticles for electrocatalytic reactions. Recent studies showed that using polymer N-heterocyclic carbenes and thiols of different hydrophilicity, including hydrophobic polystyrene (PS), hydrophilic polyethylene oxide (PEO), and zwitterionic poly(2-methacryloyloxyethyl phosphoryl choline) (polyMPC) and poly(poly(perfluoro-n-octyl 2-methacryloyloxyethyl choline phosphate) (poly(PFO-MCP)), the electrochemical CO2 reduction reactions on gold nanoparticles can achieve a CO Faradaic efficiency of over 90% (NHC-PS) and 80% (trithioester-poly(PFO-MCP)) while the partial current density for hydrogen evolution reactions decrease by more than 50%.1,2 To improve the understanding of how polymer ligands modulate the reaction microenvironment, molecular dynamics simulations were employed to investigate gold surfaces functionalized by the four different polymer ligands. The simulations showed that despite the low solubility of water in PS, the limited surface grafting density creates significant free volume in the PS ligand layer, leading to large droplets of water clusters, as characterized by short-range hydrogen bonding and a lack of long-range order. In contrast, water permeates into the fluorinated zwitterionic poly(PFO-MCP) layer more extensively to form diffuse, continuous chains that adsorb preferentially on the zwitterions. Dissolved CO2 molecules are preferentially located in the ligand layer of these two polymers while their diffusion exhibits strong anisotropy in the zwitterionic case. These results provide insights into the rich solution microenvironments that can be created by designer polymer ligands, suggesting new venues for reactivity control in electrochemical reactions.
References
(1) Luo, Q.; et al. Why Surface Hydrophobicity Promotes CO2 Electroreduction: A Case Study of Hydrophobic Polymer N -Heterocyclic Carbenes. Chem. Sci. 2023, 14, 9664–9677.
(2) Luo, Q.; et al. Fluorinated Polymer Zwitterions on Gold Nanoparticles: Patterned Catalyst Surfaces Guide Interfacial Transport and Electrochemical CO2 Reduction. Nanoscale 2024, 16, 15558–15567.
