CONICET | Buscador de Institutos y Recursos Humanos

Iron porphyrins FeP are of high interest in electrocatalysts developing for the oxygen reduction reaction (ORR) in replacement to Pt, which is the best catalyst for ORR but too expensive and ambiently scarce1,2. The technological applications require immobilizing FeP on the surface. Many alternatives have been explored to bring FeP to substrate surfaces resulting in different orientations2,3,4, interaction with the substrate (Van der Walls or covalent bounding), and chemical nature, etc. All these final structures of the FeP on a substrate would affect the ORR performance and this should be taken into account 5. In this work, we will present the influence on the ORR of the final orientation of 5,10,15,20-Tetrakis(4-phenyl) iron(III) porphyrin (FeTPP) on Au surfaces achieved by immobilization of FeTPP to the surface by two different preparation methods. One method uses physical vapor deposition of FeTPP on ultra-high vacuum (UHV) conditions which creates self-assembly monolayers of FeTPP lying flat on the surface (Figure 1.a). A second method consists in electrografting of the diazonium salt of the FeTPP in presence of an excess of the radical scavenger, 2,2-diphenyl-1-picrylhydrazil (DPPP) in order to favor monolayer grown, followed by metalation in solution. This second method creates monolayers of FeTPP orientated quasi perpendicular to the surfaces (figure 1.b). Both parallel and perpendicular configurations have been characterized by atomic force microscopy (AFM), scanning tunnel microscopy (STM), X-ray photoelectron spectroscopy (XPS) and electrochemical quartz crystal microbalance (EQCM). Finally, the influence of the orientation and chemical nature of the FeTPP monolayer on the ORR performance has been evaluated by lineal scan voltammetry (LSV) in alkaline solution.