Overpotential-dependent shape evolution of gold nanocrystals grown in a deep eutectic solvent

This paper reports an overpotential-dependent shape evolution of gold nanocrystals (Au NCs) in a choline chloride-urea (ChCl-urea) based deep eutectic solvent (DES). It was found that the growth overpotentials play a key role in tuning the shape of Au NCs. The shape evolution of Au NCs successively from concave rhombic dodecahedra (RD) to concave cubes, octopods, cuboctahedral boxes, and finally, to hollow octahedra (OH) was achieved by carefully controlling the growth overpotentials in the range from -0.50 to -0.95 V (vs. Pt quasi-reference electrode). In addition, the presence of urea was important in the shape evolution of Au NCs. The surface structure of the as-prepared Au NCs was comprehensively characterized by scanning electron microscopy (SEM), transmission electron microscopy (TEM) and electrochemical studies. It was demonstrated that the electrocatalytic activity of the as-prepared Au NCs for D-glucose electrooxidation was sensitively dependent on their morphologies. The results illustrated that the dehydrogenated glucose adsorbed on concave RD and concave cubic Au NCs was preferentially transformed to gluconolactone at low electrode potentials. Subsequent gluconolactone oxidation occurred favorably on octopods with {111}-truncated arms and hollow OH at high electrode potential. This study opens up a new approach to develop the surface-structurecontrolled growth of Au NCs by combining DES with electrochemical techniques. In addition, it is significant for the tuning of the electrocatalytic properties of NCs.