Electrochemical Scanning Tunneling Microscopy Investigations of FeN4-Based Macrocyclic Molecules Adsorbed on Au(111) and Their Implications in the Oxygen Reduction Reaction

Electrochemical scanning tunneling microscopy (EC-STM) has become a reference among in operando techniques for probing the surface at molecular and atomic levels, allowing the fundamental processes occurring at the microscopic scale to be understood while an electrochemical reaction is occurring. Metal-porphyrins and metal-phthalocyanines (MN4) are synthons in biological molecules and have been successfully employed in the homogeneous as well as heterogeneous catalysis of many reactions. Therefore, studying the behavior in situ at the solid/liquid interface of these molecules allows information on their electronic and topographic structures to be obtained. Herein, Fe(II)- and Fe(III)-coordinated phthalocyanines were examined by using the EC-STM technique. An Au(111) single crystal was used as substrate to be functionalized with Fe-phthalocyanines. These molecules were characterized in their ability to catalyze the oxygen reduction reaction, which is of great interest, especially in fuel cell technology. The FeN4 molecules in the form of an adlayer represent the catalyst material, which is probed under potential control in 0.1 M HClO4 by EC-STM, with the aim to obtain information about the O2 adsorption/reduction process.