Solution and solid phase electrochemical behaviour of [Os(bpy)3]3[P2W18O62]

[Os(bpy)3]3[P2W18O62] has been synthesised and characterised by elemental analysis,spectroscopic (UV/Vis, IR spectroscopy) and electrochemical techniques. In 0.1M Bu4NPF6DMSO the complex shows a series of redox couples associated with the Os3+/2+ and bipyridine ligands of the cationic [Os(bpy)3]2+ moiety and the tungsten-oxo framework of the associated Dawson parent heteropolyanion, [P2W18O62]6-. At this electrolyte concentration the Os3+ redox form of the complex was seen to adsorb onto the electrode surface. When the electrolyte concentration is lowered to 0.01M Bu4NPF6 in addition to the Os3+/2+ redox couple,the redox process associated with the [P2W18O62]8-/7- couple also exhibited properties indicating surface based processes were present. Electroactive films of the complex were formed on carbon macroelectrodes by the redox switching of the transition metal within the complex. Voltammetric investigations into the film’s behaviour in a range of buffer solutions(pH 2.0, 4.5 and 7.0) were performed. The films were found to possess better stability in acidic pH and the same pH dependence for the tungsten-oxo framework of the heteropolyanions as in solution. Solid state electrochemical measurements on mechanically attached microparticles of the complex were performed, with the effect of both the nature and concentration of the aqueous electrolyte on this behaviour being investigated. Upon redox switching between the Os2+/3+ redox states there is an associated insertion/expulsion of anions from/to the solution phase. Scanning electron micrographs of these solid state films were attained before and after redox cycling

Electrochemical characterisation of conducting polymer layers and their use as gas sensors

The main aim of this work was to develop an SO2 sensor based upon a conducting polymer. The methodology and properties of a conducting polymer sensor along with the electrochemical characterisation of various polypyrrole layers is described. It was found that polypyrrole layers containing Copper (11) Phthalocyanine - 3,4',4", 4"'-tetrasulphonate anions (PPTSP), as the dopant, upon electrochemical switching exhibit cation movement in and out of the polymer matrix. A concentration, pH, temperature and scan rate study was performed on the process of cation movement. Also anions, such as CIO4 ", dodecylbenzenesulphonate (DBS) were employed as the dopants within the polypyrrole matrix. In this work it is described that the low level of non-faradaic current, characteristic of PPDBS layers, was due to the presence of the DBS anion in solution rather than the polymer morphology. Differential Pulse Voltammetry is applied to various polypyrrole layers and sigmoidal differential current outputs were obtained. A model is proposed for this behaviour which includes a set of resistances in parallel. Potential Step experiments were also performed on the polypyrrole layers. A transmission line model is proposed to explain the behaviour of the polymer film. For several electroconducting polymers spectroelectrochemical studies were carried out. The absorption spectra are quantitatively analysed using the Nemst equation by a 'Monomer Unit Model. The reaction between pyrrole and tetracyanoethylene (TCNE) was studied electrochemically and spectroscopically. It was found that TCNE forms a charge transfer complex with pyrrole, and it is present within the PPTCNE layer as the dopant anion. The influence of solvent composition upon the ferricyanide/ferrocyanide system was investigated electrochemically. It was found that in organic solvents ferrocyanide is a strong reducing agent. Polypyrrole layers were deposited across interdigital array electrodes and their responses to various organic vapours and 5 % SO2 were investigated. The use of Prussian Blue films as possible overlayers upon the polypyrrole layers is described. Also solid state voltammetry was performed upon Prussian Blue films, and when these mixed valent films were exposed to certain saturated vapours in nitrogen, good reversible responses were obtained. Also the interaction of organic vapours and polypyrrole films, deposited upon ITO electrodes, was investigated by UV/vis spectroscopy

How close are ground-based Fabry-Perot thermospheric wind and temperature measurements to exospheric values? A simulation study

Ground-based Fabry-Perot interferometers (FPIs) have been used extensively to determine thermodynamical and hydrodynamical properties of the upper atmosphere by measuring emission line profiles from the O(1D) nightglow at high spectral resolution. The resulting thermospheric winds and temperatures are normally referred to the altitude of the peak of the O(1D) emission layer, near 250 km, and the effects of wind shear and temperature gradations along the line of sight are neglected. In order to quantify the significance of these effects, and to obtain a better understanding of the "effective" (volume-emission-rate-weighted) altitude of the FPI measurement, a computer simulation of the measurement technique has been performed, incorporating realistic profiles of winds, temperatures and O(1D) volume emission rates along the instrumental line-of-sight. The atmospheric profiles used for the simulations are derived from a recently-developed thermospheric computer subroutine based on the predictions of the NCAR thermospheric general circulation model. The simulation code is used to calculate synthetic FPI spectrograms for different viewing geometries and FPI station locations, and the spectrograms are analyzed using standard data reduction techniques to derive fitted winds and temperatures. These are then compared with the atmospheric profiles used as input to the simulation code to determine the effective altitude of each simulated measurement and to study the differences between recovered winds and temperatures and the corresponding exospheric values. A first investigation using the simulation code for geophysical conditions corresponding to December solstice at solar maximum has indicated that FPI-derived Doppler temperatures may be lower than exospheric temperatures by ~10% in the winter hemisphere and ~15% in the summer hemisphere. Furthermore, FPI measurements of neutral winds, particularly at high latitudes, can differ appreciably from exospheric values due to the weighting of the FPI measurement to altitudes near ~250 km.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/26565/1/0000104.pd

On the dynamics and composition of the high-latitude thermosphere

Recent experimental measurements of the dynamics of the neutral upper thermosphere have demonstrated the important roles of ion-drag and Joule heating processes in establishing the basic neutral wind morphology and controlling neutral composition, particularly in the high-latitude region. Instruments on the Dynamics Explorer-2 spacecraft (DE 2), for example, were capable of measuring the three-dimensional vector neutral wind and ion drift in the thermosphere along the orbital track, together with constituent densities and temperatures. Ground-based optical and radar measurements of winds and temperatures from observatories in Greenland have contributed additional measurements of thermospheric neutral wind velocities and ionospheric parameters. The comprehensive nature of these various data sets has enabled more stringent experimental constraints to be placed on the numerical models of the region (thermosphere-ionosphere general circulation models, TIGCMs), leading to an improved theoretical understanding of the important physical processes that control thermospheric circulation and variability. In addition, the measurements have enabled the development of semi-empirical models of thermosphere dynamics which can be used in various theoretical studies. The Vector Spherical Harmonic (VSH) model, for example, provides a description of global thermospheric state variables (wind, temperature and density), using a combination of empirical data and NCAR-TIGCM calculations. This paper presents a brief review of some of the more recent progress made in this area by the team of researchers at the University of Michigan, with emphasis on the interpretation of experimental measurements made from DE 2 and from ground-based observatories in Thule and Sondrestromfjord, Greenland. Comparisons between individual data sets from these sources and the VSH model are also presented.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/29167/1/0000212.pd

The Astropy Problem

The Astropy Project (http://astropy.org) is, in its own words, "a community effort to develop a single core package for Astronomy in Python and foster interoperability between Python astronomy packages." For five years this project has been managed, written, and operated as a grassroots, self-organized, almost entirely volunteer effort while the software is used by the majority of the astronomical community. Despite this, the project has always been and remains to this day effectively unfunded. Further, contributors receive little or no formal recognition for creating and supporting what is now critical software. This paper explores the problem in detail, outlines possible solutions to correct this, and presents a few suggestions on how to address the sustainability of general purpose astronomical software

Surface Immobilisation of Transition Metal Substituted Krebs Type Polyoxometalates, [X 2 W 20 M 2 O 70 (H 2 O) 6 ] n-(X = Bi or Sb, M = Co 2+ or Cu 2+ ), by the Layer by Layer Technique

A series of transition metal (i.e. Cu 2+ and Co 2+ ) substituted Krebs type Polyoxometalates (POMs), of the general formula [X 2 W 20 M 2 O 70 (H 2 O) 6 ] n- , X = Sb or Bi, M = Co(II) or Cu(II), have been successfully immobilised onto carbon electrode surfaces through the employment of the layer-by-layer (LBL) technique. This involved the construction of alternating anionic POM, [X 2 W 20 M 2 O 70 (H 2 O) 6 ] n- , layers and the cationic metallodendrimer, Ru(II)-metallodendrimer as the cationic layers, in addition to a [poly(diallyldimethylammonium chloride)] PDDA base layer. Stable multielectron redox couples associated with the W-O framework, for the Krebs type POMs, and the Ru(III/II) for the metallodendrimer, were clearly observed upon layer construction and redox switching within the pH domain of 2 to 6.5. The constructed multilayer assemblies exhibited pH dependent redox activity and thin layer behaviour up to 100 mV s -1 . The porosity and permeability of the individual multilayer assemblies towards an anionic probe was determined by AC impedance and cyclic voltammetry. The surface morphology of each multilayer was also determined by Atomic Force Microscopy (AFM). Keywords

Solution and solid phase electrochemical behaviour of [Os(bpy)3]3[P2W18O62]

[Os(bpy)3]3[P2W18O62] has been synthesised and characterised by elemental analysis,spectroscopic (UV/Vis, IR spectroscopy) and electrochemical techniques. In 0.1M Bu4NPF6DMSO the complex shows a series of redox couples associated with the Os3+/2+ and bipyridine ligands of the cationic [Os(bpy)3]2+ moiety and the tungsten-oxo framework of the associated Dawson parent heteropolyanion, [P2W18O62]6-. At this electrolyte concentration the Os3+ redox form of the complex was seen to adsorb onto the electrode surface. When the electrolyte concentration is lowered to 0.01M Bu4NPF6 in addition to the Os3+/2+ redox couple,the redox process associated with the [P2W18O62]8-/7- couple also exhibited properties indicating surface based processes were present. Electroactive films of the complex were formed on carbon macroelectrodes by the redox switching of the transition metal within the complex. Voltammetric investigations into the film’s behaviour in a range of buffer solutions(pH 2.0, 4.5 and 7.0) were performed. The films were found to possess better stability in acidic pH and the same pH dependence for the tungsten-oxo framework of the heteropolyanions as in solution. Solid state electrochemical measurements on mechanically attached microparticles of the complex were performed, with the effect of both the nature and concentration of the aqueous electrolyte on this behaviour being investigated. Upon redox switching between the Os2+/3+ redox states there is an associated insertion/expulsion of anions from/to the solution phase. Scanning electron micrographs of these solid state films were attained before and after redox cycling

Assembly, electrochemical characterisation and electrocatalytic ability of multilayer films based on [Fe(bpy) 3] 2+, and the Dawson heteropolyanion, [P2W18O62]6-.

Successive adsorption onto a glassy carbon electrode of the Dawson heteropolyanion,[P2W18O62]6-, and the multiply charged cation [Fe(bpy)3]2+, resulted in the formation of stable multilayer assemblies on the electrode surface. Surface coverages were found to be typical of monolayer coverages for multilayer systems. Cyclic voltammetric studies of the assembly in aqueous. 0.5M NaHSO4, gave a range of redox couples associated with the Fe3+/2+ redox system, of the cationic [Fe(bpy)3]2+ moiety and the tungsten-oxo framework of the Dawson parent heteropolyanion, [P2W18O62]6-. It was possible to immobilise up to thirty monolayers, with the system exhibiting well behaved redox behaviour. The stability of the assembly towards redox switching was investigated, with it being found be extremely stable once the outer layer is anionic in nature. The immobilised film was also tested for electrocatalytic activity for the reduction of nitrite, hydrogen peroxide and bromate, and was shown to be an efficient electrocatalyst

Voltammetric Behaviour, Homogeneous Charge Transport Dynamics and Electrocatalytic Properties of an Os2+ Functionalised Pyrrole Monomer

The Os2+ functionalised pyrrole monomer, Osmium-bis-N,N’-(2,2’-bipyridyl)-N-(pyridine-4-ylmethyl-( 8-pyrrole-1yl-octyl)-amine)chloride, 1, has been synthesised and characterised by spectroscopic (UV/Vis, 1H NMR, IR spectroscopy) techniques and cyclic voltammetry. Solution phase studies of 1 gave a redox couple associated with the Os3+/2+ and an irreversible wave associated with the oxidation of the pyrrole moiety. Attempts to form stable polymeric films of 1 onto vitreous carbon electrodes, by homopolymerisation, proved unsuccessful. However electroactive films of 1 were obtained by the electrooxidation of 1 through the Os3+/2+ couple in low dielectric media such as toluene/acetonitrile mixtures. The efficiency of film deposition and properties depend upon the supporting electrolyte and the solvent employed. Films formed in mixtures of acetonitrile and low dielectric constant solvents (dichloromethane and toluene) are electrochemically active and exhibit a redox couple associated with the Os3+/2+ system. The voltammetric behaviour of these solid state films was investigated in both aqueous and non-aqueous solvents with a variety of supporting electrolytes. Upon redox switching between the Os3+/2+ redox states the solid-state chargetransfer processes are coupled to the insertion/expulsion of anions from/to the solution phase.Scanning electron microscopy reveals that films formed in the presence of acetonitrile exhibit different morphology than films formed in acetonitrile-free solutions. Slow and fast linear sweep voltammograms have been employed to provide an absolute determination of the fixed 2 site concentration as 1.5M and an apparent diffusion coefficient of 5.2 x 10-12 cm2 s-1 in 0.3MKCl. Electroactive films of 1 were then investigated for their electrocatalytic ability towards the oxidation of ascorbic acid in acidic medium. The anodic oxidation peak current was linearly dependent on the ascorbic acid concentration and a linear calibration curve was obtained in the range 0.1 – 2x10-3 M of ascorbic acid with a correlation coefficient of 0.9993. The detection limit (3s) was found to be 5.5 x 10-5M