Unusual Demetalation and Ordered Adsorption of a Pyridine-Appended Zinc Phthalocyanine at Metal–Electrolyte Interfaces Studied by in Situ Scanning Tunneling Microscopy and X-ray Photoelectron Spectroscopy

Abstract

A combination of cyclic voltammetry, in situ electrochemical scanning tunneling microscopy (EC-STM), and ex situ X-ray photoelectron spectroscopy (XPS) studies was employed to investigate the electrochemical behavior and to characterize the structure of adsorbed layers of a redox-active pyridine-appended zinc phthalocyanine (ZnPc) at Cu(100)/electrolyte interfaces. Additional cyclic voltammograms (CVs) of a HOPG electrode in phthalocyanine- and iodide-containing electrolyte showed four redox peak pairs related to the phthalocyanine macrocycle. Focusing on the reduction processes, the four observed cathodic waves were assigned to four single electron transfer steps causing four successive reductions of the phthalocyanine. Due to its narrow potential window, the CV of Cu(100) in the same electrolyte covers only the first three reduction features in the acidic solution superimposed by the CuI formation/dissolution processes. Surprisingly, the XPS data from the iodide and phthalocyanine covered Cu(100) surfac...