Stability, Assembly, and Particle/Solvent Interactions of Pd Nanoparticles Electrodeposited from a Deep Eutectic Solvent

Supported nanoparticle synthesis and assembly have application in a wide range of modern day applications. Key to the manipulation of the particle assembly is an understanding of the interaction between the particles and solvent. Here, we employ a comprehensive in situ approach, together with ex situ SEM imaging, to study supported palladium nanoparticles, electrodeposited from a 2:1 urea:choline Cl- DES. Using cyclic voltammetry, we confirm the expected adsorption of electroactive species onto the deposited particles. On the basis of our experimental results, we conclude that the electrodeposited nanoparticles assemble into 2-D superstructures, rich in adsorbed species. The abundance of these adsorbed species, within the superstructure, induces an anionic layer above them, which can be observed by ultrasmall-angle X-ray scattering (USAXS) as well as electrochemical impedance spectroscopy (EIS). The surface charge of the particles is, therefore, not neutralized locally, as is the case with traditional colloidal systems. We also show that these otherwise stable nanoparticles readily aggregate when the DES is removed. Thus, the stability of these particles is contingent upon the presence of the DES.