Ellipsometry and standard electrochemical techniques are used to deter ~ mine whether, and if so, how the thickness of an anodic oxide film affects the catalysis of the oxygen evolution reaction at platinum. A prereduced electrode is first polarized in sulfuric acid solution with a constant current density, iD for a given time and then the thickness, d, of the anodic film and the electrode potential, V, are determined for various current densities i ~ ip. It is found that the thickness of the oxide film affects the catalytic activity in an exponential way, Le. * Electrochemical Society Active Member.

Die Kinetik des Oxidfilmwachstums an Pt‐Anoden wird bei beginnender Polarisation bei verschiedenen konstanten Stromdichten untersucht.

We report a series of 3d–4f complexes {Ln2Cu3(H3L)2Xn} (X=OAc−, Ln=Gd, Tb or X=NO3 −, Ln=Gd, Tb, Dy, Ho, Er) using the 2,2′‐(propane‐1,3‐diyldiimino)bis[2‐(hydroxylmethyl)propane‐1,3‐diol] (H6L) pro‐ligand. All complexes, except that in which Ln=Gd, show slow magnetic relaxation in zero applied dc field. A remarkable improvement of the energy barrier to reorientation of the magnetisation in the {Tb2Cu3(H3L)2Xn} complexes is seen by changing the auxiliary ligands (X=OAc− for NO3 −). This leads to the largest reported relaxation barrier in zero applied dc field for a Tb/Cu‐based single‐molecule magnet. Ab initio CASSCF calculations performed on mononuclear TbIII models are employed to understand the increase in energy barrier and the calculations suggest that the difference stems from a change in the TbIII coordination environment (C 4v versus Cs).

The kinetics of growth of anodic oxide films at platinum in 0.1N H2SO4 solution have been studied by in situ chronoellipsometry both under constant potential and under constant current mode of polarization. Two regions of growth can now be distinguished. In the first, the kinetics of growth satisfy the formalism of the Cabrera‐Mott model of high field assisted formation and migration of ions in the oxide phase, i.e. i=i0exp][αnormalΔVnormalfdwhere normalΔVnormalf is the potential difference across the oxide film and d is the film thickness. In the first region, oxide growth is the only reaction that occurs at the electrode. Following this initial growth, which is already completed at a thickness of 4–6Å depending on the rate of growth, oxygen starts to evolve but the oxide film continues to grow though now with a reduced rate. The kinetics of growth in the second region are described by an equation of the formi=i0exp][−d)(td0+normalΔVnormalf)(tV0This equation for the extended growth of platinum oxide films is diametrically different from that which describes the initial growth. The complex nature of oxide growth at platinum is discussed in relation to the oxygen evolution reaction.

Constant current charging curves from 10 -6 to 10 -1 A-cm -2 are used to study the mechanism of growth of anodic oxide films at platinum in H2SO4 solutions. At any constant current density the potential initially changes linearly with time. In this linear region no 02 is evolved. The linear region is followed by a region Jn which potential changes logarithmically with time while oxygen evolution becomes the predominant reaction. The thickness of the oxide films at which the transition occurs depends on the applied current density but for all current densities it is less than 10A. Both in the linear and the logarithmic region the ellipsometric thickness-time relationships essentially parallel the V-t relationships. The rate of growth is described bywhere d is the thickness and Vo the potential at which oxide film starts to grow. From the transfer coefficient a, that is equal to 158 A-V -1, it was deduced that the oxide phase is composed of divalent platinum ions, i.e., the oxide phase is Pro. It is suggested that the rate-determining step is a process at the metal/oxide interface rather than a process at the oxide/solution interface or a process within the bulk of oxide. The distribution of the potential between the oxide film and the double layer is discussed. It is shown that the potential difference across the solution double layer is constant for the growth at current densities examined here. This is possible if the electrochemical reaction in the double layer is fast. ) unless CC License in place (see abstract). ecsdl.org/site/terms_use address. Redistribution subject to ECS terms of use (see 128.218.248.200 Downloaded on 2015-04-13 to IP ) unless CC License in place (see abstract). ecsdl.org/site/terms_use address. Redistribution subject to ECS terms of use (see 128.218.248.200 Downloaded on 2015-04-13 to IP