Adlayer Structures and Electrocatalytic Activity for O₂ of Metallophthalocyanines on Au(111):  In Situ Scanning Tunneling Microscopy Study

Abstract

Adlayers of cobalt(II) and copper(II) phthalocyanines (CoPc and CuPc) prepared on Au(111) from CoPc- and CuPc-saturated benzene solutions were investigated in 0.1 M HClO4 by using cyclic voltammetry and in situ scanning tunneling microscopy (STM). The CoPc-modified Au(111) electrode was found to enhance the electrochemical reduction of O2 to H2O2, whereas the CuPc-modified Au(111) electrode showed no electrocatalytic activity for O2 reduction. High-resolution STM images revealed the characteristic shape, internal structure, and orientation of each CoPc and CuPc molecule in ordered domains. Both CoPc and CuPc molecules formed three packing arrangements on Au(111) surface, i.e., one rectangular arrangement on reconstructed Au(111) and two hexagonal arrangements on Au(111)−(1 × 1), depending on the surface coverage. The center cobalt ion in CoPc appeared as the brightest spot in the STM image, whereas the copper ion in CuPc appeared as a dark spot.

The Effect of Polarity on Coadsorbed Molecular Nanostructures of Substituted Phthalocyanine and Thiol Molecules

“…[13] The characteristic shape, internal structure and orientation of each CoPc and CuTPP molecule were revealed by high-resolution ECSTM images. [14] Using alkylated phthalocyanines and porphyrins, submolecular features of the molecular cores and the interdigitated alkyl groups were clearly observed by our group. Two packing symmetries were observed for copper(II) 2,3,9,10,16,17,23,24-octakis(octyloxy)-29H,31H-phthalocyanine (CuPcOC8), and appreciable contrast variations were recorded with changing bias polarity.…”

On the topography multiplicity of non-planar titanyl (IV) phthalocyanine molecules and the STM imaging mechanism

“…TiOPc adlayers show high stability and can endure repeated STM scanning under ambient conditions. Repeated STM experiments demonstrate that TiOPc molecules exhibited various shapes while the packing arrangements kept hexagonal symmetry, which is dramatically different from the other phthalocyanines reported previously, such as CuPc, CoPc, VOPc etc., [23][24][25][26][27][28]. The reported molecular topographies of Pcs and MPcs show characteristic fourfold shape, although the packing arrangements have either quadratic or quasi-hexagonal symmetries.…”

“…To date, a number of phthalocyanine adlayers have been investigated by STM and the reported topography appeared with fourfold shape independent of packing arrangements and imaging conditions [23][24][25][26][27][28]. Most un-substituted metallophthalocyanines (MPcs) were imaged under UHV condition or in solution and the homogeneous MPcs adlayers by STM under ambient conditions were observed with the aid of co-adsorption methods [29,30].…”

Electrochemically controlled self-assembled monolayers characterized with molecular and sub-molecular resolution

“…Adlayer structures of both thiol 41,42,64,75 and nonthiol containing molecules [29][30][31]44,[50][51][52][53][54]76 have been found to display notable electrochemical potential dependence, suggesting that the electrochemical potential is a key controlling parameter in the monolayer formation. The main objective of the present communication is to illustrate potential dependent SAM structures and formation processes by examples of SAM structures at atomically flat single-crystal gold surfaces in aqueous solution.…”