Enhancement of the Catalytic Activity of Fe Phthalocyanine for the Reduction of O₂ Anchored to Au(111) via Conjugated Self-Assembled Monolayers of Aromatic Thiols As Compared to Cu Phthalocyanine

Abstract

We have prepared self-assembled monolayers (SAMs) of 4-aminothiophenol (4-ATP) and 1-(4-mercaptophenyl)-2,6-diphenyl-4-(4-pyridyl)pyridinium tetrafluoroborate (MDPP) functionalized with iron phthalocyanine (FePc) and copper phthalocyanine (CuPc) adsorbed on gold (111) electrodes. The catalytic activity of these SAMs/MPc was examined for the reduction of O 2 in aqueous solutions and compared to that of bare gold and with gold coated directly with preadsorbed MPc molecules. Scanning tunneling microscopy (STM) studies confirm the functionalization of the 4-ATP by MPc. STM images reveal that iron phthalocyanine molecules are chemically anchored to 4-aminothiophenol organic monolayers, probably having an "umbrella" type orientation with regards to the surface. The electrocatalytic studies carried out with Au/4-ATP/FePc and Au/ MDPP/FePc electrodes show that the O 2 reduction takes place by the transfer of 4-electron to give water in contrast to a 2-electron transfer process observed for the bare gold. The modified electrode obtained by simple adsorption of FePc directly to the Au(111) surface still promotes the 4-electron reduction process, but it shows a lower activity than the electrodes involving SAMs with FePc molecules positioned at the outmost portion of the selfassembled monolayers. The activity of the electrodes increases as follow: Au < Au/FePc < Au/4-ATP/FePc < Au/MDPP/FePc with the highest activity when FePc molecules are more separated from the Au surface. In contrast, the less active CuPc shows almost the same activity in all three configurations. Theoretical calculations suggest the importance of the back-bonding into the adduct formation, showing the relevance of the supporting gold surface on the electron-transfer process mediated by anchoring ligands.

Exploring the Effect of Gold Support on the Oxygen Reduction Reaction Activity of Metal Porphycenes

“…Fe−Pthalocyanines anchored on Au(111) via self‐assembled monolayers of aromatic thiols and Co−tetraphenylporphyrin on Au(111) surface revealed improved ORR activity compared to their homogeneous counterparts ,. Graphene supported iron‐pthalocyanines have also shown enhanced ORR activity compared to platinum .…”

Polyaniline nanostructure electrode: morphological control by a hybrid template

“…Figure 1b shows the electrochemical characterization using cyclic voltammetry of 4-aminothiophenol SAMs built up on the gold layer at the inner base of the pores of the AAO template. The reductive desorption process of the SAMs in 0.1 M NaOH at 0.05 V/s shows a principal peak at −0.8 V, which is typical of thiol used here, indicating a one-electron transfer for the desorption of the 4-ATP from the gold surface [20]. Two additional more negative broad weak peaks are observed in the voltammetric profile, indicating the electrodesorption of 4-ATP molecules from other kinds of surface domains or from surface defects of the polycrystalline gold layer at the inner base of the AAO pores.…”

Advances in bonding and properties of inorganic systems from relativistic calculations in Latin America

“…The use of cluster models for the interaction between Au surfaces and different substrates has been explored by Mendizabal and coworkers in order to further understand the catalytic aspects of metallophthalocyanines adsorbed on gold‐electrode, accounting for the nature of these interactions . Their results demonstrate the great capabilities to further modify the catalytic behavior via chemical modification of the system.…”