Underpotential deposition of silver on gold from deep eutectic electrolytes

The electrochemical behavior of Ag(I) in choline chloride-urea medium (ChCl-U) has been investigated at a gold electrode using cyclic voltammetry. Cyclic voltammograms revealed a diffusion limited reduction wave coupled on the reverse sweep with an oxidation wave that corresponds to the dissolution of a bulk deposit. Beside these main peaks, we have highlighted other peaks at potentials more positive than the thermodynamic potential of silver bulk deposition. Experiments at various potential scan rates have indicated that, contrary to the main reduction peak, these peaks are indicative of a surface process that corresponds to an underpotential deposition (upd) of silver. The absence of upd at glassy carbon or platinum electrodes in ChCl-U has ruled out the influence of silver speciation on the existence of the upd process. The occurrence of silver upd on gold is moreover not linked to the nature of the H-bond donor (urea, ethylene glycol or oxalic acid) of the choline choride DES.