Asymmetric Pulse Electrodeposition of High-Index Faceted Gold Nanostructures for 5-Hydroxymethylfurfural Oxidation

This work reports the electrodeposition of high-index faceted gold particles resembling rhombic hexecontahedrons in choline chloride urea deep eutectic solvent through the application of asymmetric potential pulses. Potential pulses alternated between cathodic potentials ranging from -0.20 V to -0.25 V vs. Ag/AgCl and an anodic limit of 0.35 V vs. Ag/AgCl near the gold dissolution onset. While the cathodic pulse duration was fixed at 0.5 s, the anodic pulse duration varied from 0.5 s to 2.5 s to study its influence on crystal growth. Symmetric pulses produced poorly defined structures, whereas longer anodic pulses induced tetrahexahedral and truncated bipyramidal nanostructures. Further increasing the reduction overpotential induced a shape transition to rhombic hexecontahedral morphologies, attributed to the ligand effect of urea. Blank cyclic voltammograms in NaOH solution and Pb underpotential deposition measurements on pulse-deposited gold indicated the formation of structures enclosing [n(110) × (111)] facets. The electrocatalytic performance of the pulse deposited nanostructures towards 5-hydroxymethylfurfural oxidation was tested, showing strong activity for partial aldehyde oxidation and moderate activity for the oxidation of the alcohol moiety. This study demonstrates that asymmetric pulse electrodeposition offers a promising approach to tailoring surface geometries and highlights the role of deep eutectic solvents in shaping crystal structures.