Evolution of Structure and Activity of Alloy Electrocatalysts during Electrochemical Cycles: Combined Activity, Stability, and Modeling Analysis of PtIrCo(7:1:7) and Comparison with PtCo(1:1)

This study explores the changes in bulk composition/structure and oxygen reduction activity of two alloys, Pt₇IrCo₇ and PtCo, caused by Co leaching during electrochemical cycles and as a result of membrane electrode assembly (MEA) fabrication procedures. Exposure to liquid electrolyte and electrochemical cycles in a rotating disc electrode (RDE) environment resulted in substantial Co loss and no stabilization from the low levels of Ir used in the ternary material. The true composition of the ternary material was determined as Pt₈IrCo₃ following initial exposure to 0.1 M HClO₄ (before cycling) and Pt₁₁IrCo₄ after 5000 cycles. Density functional theory (DFT) modeling of the cycled catalyst compositions indicated that structures with Pt-rich upper layers would show the highest stability; however, addition of 0.25 ML oxygen adsorption favored Co segregation from second and third atomic layers. The high initial activities (>0.44A/mgPt) achieved in the RDE environment decreased with cycles and were not reproduced in MEAs. X-ray diffraction (XRD) analysis revealed a measurable increase in lattice parameter caused by the MEA preparation procedure, consistent with Co (and some Ir) leaching into the ionomer phase and relaxation of the lattice. MEA fabrication procedures and cycling in 1 M H₂SO₄ at 80^◦C showed greater changes to catalyst structure and increased Ir and Co loss compared to exposing the catalyst to RDE like conditions (0.1 M HClO₄, RT) explaining the observed discrepancy in activity between RDE and MEA

Voltammetric and electrochemical impedance study of ferrocenyl containing beta-peptide monolayers on gold

An investigation of the kinetics of electron transfer though a self-assembled monolayer containing long chain alkanethiol and β-peptide components and a terminating ferrocene group has been carried out at a polycrystalline gold electrode. Cyclic voltammetry and electrochemical impedance spectroscopy in aqueous and mixed aqueous-methanol solutions showed the rate of electron transfer varied from approximately 5 in water to 29 s-1 in methanol. This difference is attributed to a change in the alkanethiol tilt angle in the film in response to hydrogen bonding disruption of the peptide to allow greater molecular motion during electron transfer. © 2011 American Chemical Society.Paula A. Brooksby, Kelly H. Anderson, Alison J. Downard, and Andrew D. Abel

Organization of Alkane Amines on a Gold Surface: Structure, Surface Dipole, and Electron Transfer

Surface molecular self-assembly is a fast advancing field with broad applications in molecular electronics, sensing and advanced materials. Although a large number of practical systems utilize alkanethiols, there is increasing interest in alkylamine self-assembled monolayers (SAMs). In this article, the molecular and electronic structure of alkylamine SAMs on Au surfaces was studied. It was found that amine-terminated alkanes self-assemble, forming a compact layer with the amine headgroup interacting directly with the Au surface and the hydrocarbon backbone tilted by around 30° with respect to the surface normal. The dense layers formed substantially decrease electron tunneling across the metal/solution interface and form a dipole layer with positive charges residing at the monolayer/vacuum interface.Fil: de la Llave, Ezequiel Pablo. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Ciudad Universitaria. Instituto de Química, Física de los Materiales, Medioambiente y Energía. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Instituto de Química, Física de los Materiales, Medioambiente y Energía; ArgentinaFil: Clarenc, Romain. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Departamento de Química Inorgánica, Analítica y Química Física; ArgentinaFil: Schiffrin, David J.. University of Liverpool; Reino UnidoFil: Williams, Federico José. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Ciudad Universitaria. Instituto de Química, Física de los Materiales, Medioambiente y Energía. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Instituto de Química, Física de los Materiales, Medioambiente y Energía; Argentin