A combined EC-STM and EC-AFM investigation of the sulfate adsorption on a Cu(111) electrode surface up to the anodic corrosion potential

Abstract

Nowadays, sulfate adsorption on single Cu(111) crystals, when immersed in diluted sulfuric acid solution, can be considered a benchmark to test the so-called electrochemical scanning tunneling microscopy (EC-STM), because the formation of a well ordered sulfate superstructure and a characteristic Moiré pattern can be detected by STM on different length scales. Clearly, EC-STM shows more difficulties in the image acquisition when the applied potential is close to or within the anodic corrosion regime, i.e., when copper undergoes a dissolution process that releases copper ions (Cu2+) into solution, because both the developed high faradaic current flowing through the sample and a significant disintegration of the electrode surface may cause severe instability during the STM scan. Here, we successfully combine the EC-STM with the EC-atomic force microscopy (EC-AFM) to extend the surface characterization towards the corrosion regime. In addition, the Cu(111) surface morphology has never been explored with EC-AFM after the copper re-deposition occurring in the reverse potential scan at EC-potentials lower than the anodic corrosion one. Consequently, our combined investigation, performed on different length scales, highlights the effects of the redox processes in the whole EC potential interval that can be explored during the cyclic voltammetry (CV).