Electrochemical scanning tunneling microscopy investigation of HOPG and silver electrodeposition on HOPG from the acid room-temperature molten salt aluminum chloride 1-methyl-3-butyl-imidazolium chloride

The electrodeposition of silver on highly oriented pyrolytic graphite (HOPG) from the acid room-temperature molten salt aluminum chloride-1-methyl-3-butyl-imidazolium chloride (molar ratio of 55/45 containing AgCl in a concentration of 0.05 mol/L) has been investigated with electrochemical scanning tunneling microscopy, cyclic voltammetry, and potential-step experiments. HOPG can be viewed on an atomic scale; at electrode potentials above +1000 mV vs the Ag/Ag+ reference it is oxidized, leading to both hole etching and protrusions. Silver electrodeposition requires an overvoltage of -300 to -350 mV. With rising overpotential, the mechanism changes from three-dimensional progressive nucleation at a finite number of active sites to three-dimensional instantaneous nucleation. In the far overpotential range the deposition mainly takes place at steps and defects between different basal planes of graphite and to a lower extent on the basal planes themselves.