SummarySimple hydroxamic acids such as formo- and aceto-hydroxamic acids have been proposed as suitable reagents for the separation of either Pu and/or Np from U in modified or single cycle Purex based solvent extraction processes designed to meet the emerging requirements of advanced fuel cycles. The stability of these hydroxamic acids is dominated by their decomposition through acid hydrolysis. Kinetic studies of the acid hydrolysis of formo- and aceto-hydroxamic acids are reported in the absence and the presence of Pu(IV) ions. The slow reduction of these plutonium(IV) hydroxamate complexes to Pu(III) aquo-ions has been characterised by spectrophotometry and cyclic voltammetry. The reductions of Pu(IV) in the presence of FHA and AHA are consistent with a mechanism in which free hydroxamic acid in solution is hydrolysed whilst Pu(IV) ions remain fully complexed to hydroxamate ligands; then at some point close to a 1 : 1 Pu(IV) : XHA ratio, some free Pu

Hydroxamic acids are salt free, organic compounds with affinities for cations such as Fe 3+ , Np 4+ and Pu 4+ and have been identified as suitable reagents for the control of Pu and Np in advanced nuclear fuel reprocessing. The results of a UV-visible-near IR spectrophotometric study of the 1:1 and 2:1 complexes formed between formo-and aceto-hydroxamic acids (FHA, AHA) and Np(IV) ions are interpreted using speciation diagrams for the identification of the species present at diferent pH and ligand to metal ratios. A kinetic model that describes the instability of the complex due to the hydrolysis of the hydroxamate moeity, previously developed for the Fe(III)-AHA complexes [1], is tested here against experimental Np(IV)-FHA data. Consequently, the complexation constant for formation of the 1:1 Np(IV)-FHA complex in nitric acid is estimated at K 1 = 2715, and indications are that complexation protects the ligand against hydrolysis at 0.1 > pH >-0.1.

The Micro-Optical Ring Electrode (MORE) is a photoelectrochemical device based on a ring microelectrode that uses the insulating material interior to the ring electrode as a light guide. In this paper, we derive asymptotic analytical expressions for the steady state, transport limited photocurrent generated at MOREs with thin microrings ((ring inner radius)/(ring outer radius) values > 0.99) for two general types of photoelectrochemical system (a) the PE (Photophysical-Electrochemical) system, wherein the photoexcited species itself is directly detected on the ring; and (b) the PCE (Photophysical-Chemical-Electrochemical) system, wherein the photoexcited species undergoes a homogeneous electron transfer reaction prior to electrochemical detection.

Hydroxamic acids (XHAs) are organic compounds with affinities for cations such as Fe 3+ , Np 4+ and Pu 4+ and have been identified as useful reagents in nuclear fuel reprocessing. Acid catalysed hydrolysis of free XHAs is well known and may impact negatively on reprocessing applications. Hydrolysis of metal bound XHAs within metal ion-XHA complexes is less understood. With the aid of speciation diagrams, we have modelled UV-visible spectrophotometric kinetic studies of the acid-catalysed hydrolysis of acetohydroxamic acid (AHA) bound to the model ion Fe(III). These studies have yielded the following for the hydrolysis of AHA in the Fe(AHA) 2+ complex at 293 K: (i) the order with respect to [H + ] during the rate determining step, m = 0.97, the same as for the free ligand, indicating a similarity of mechanism; and (ii) the rate parameter, k 1 =1.02 x 10-4 dm 3 •mol-1 •s-1 , greater than that for the free ligand, k 0 = 1.84 x 10-5 dm 3 •mol-1 •s-1 for pH >-0.5, a result consistent with a Hammett analysis of the system.

The penetration of renewable sources (solar and wind power) into the power system network has been increasing in the recent years. As a result of this, there have been serious concerns over reliable and satisfactory operation of the power systems. One of the solutions being proposed to improve the reliability and performance of these systems is to integrate energy storage devices into the power system network. Zinc-bromine batteries systems among other energy storage technologies has appeared as one of the best options. This paper presents the performance of three different electrodes feeder materials (carbon, nickel and a titanium) coupled and investigated within a fabricated ZnBr2 cell system via numerical modelling, DDPM+DEM model in ANSYS Fluent to simulate an incorporated anode zinc-electrode and COMSOL Multiphysics for the electrochemical behavior of the cell. After introducing briefly other alternatives to store energy, ZnBr2 cell systems, and its mode of operation were then discussed, before focusing on the numerical modelling and simulation and the laboratory experiments. Several extensive electrochemical experiments were implemented on the cell to achieve fast deposition of zinc onto the electrode surface during charge and fast dissolution during discharge for high performance. The mechanical action of the fluidised design of electrode is intended to improve deposit morphology, obviate the risk of dendrite growth and provide high transport rates of reactant to and from the active electrode surface. In conclusion, this paper has analyzed electrochemical techniques like chronopotentiometry, cyclic voltammetry (CV), and electrochemical impedance spectroscopy that were used to understand the behavior of the zinc bromide cells at a particular flow rate of 166.7cm 3 min −1 required to give good fluidization of the anode.

We report the fabrication and characterisation of the first graphene ring micro electrodes with the addition of a miniature concentric Ag/AgCl reference electrode. The graphene ring electrode is formed by dip coating fibre optics with graphene produced by a modified Hummers method. The reference electrode is formed using an established photocatalytically initiated electroless deposition (PIED) plating method. The performance of the so-formed graphene ring micro electrodes (GRiMEs) and associated reference electrode is studied using the probe redox system ferricyanide and electrode thicknesses assessed using established electrochemical methods. Using 220 μm diameter fibre optics, a ∼15 nm thick graphene ring electrode is obtained corresponding to an inner to outer radius ratio of >0.999, so allowing for use of extant analytical descriptions of very thin ring microelectrodes in data analysis. GRiMEs are highly reliable (current response invariant over >3,000 scans), with the concentric reference electrode showing comparable stability (current response invariant over >300 scans). Furthermore the micro-ring design allows for efficient use of electrochemically active graphene edge sites and the associated nA scale currents obtained neatly obviate issues relating to the high resistivity of undoped graphene. Thus, the use of graphene in ring microelectrodes improves the reliability of existing micro-electrode designs and expands the range of use of graphene-based electrochemical devices.

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1 Acetohydroxamatoiron (III) complexes Andrieux et al. AbstractStudies of the thermodynamics of formation of the acetohydroxamatoiron(III) complexes were carried out in acidic media at temperatures ranging from 293 to 323 K. Through the isolation of the unique UV -visible spectra of all three complexes, it was possible to determine their formation constants and deduce enthalpies and entropies of formation as well as their molar absorptivities. The enthalpies of formation of the mono-, bis-and trisacetohydroxamatoiron(III) complexes were found to be -56.4, -17.09 and +19.74 kJ•mol -1 , respectively. Following the determination of the enthalpy and entropy of formation of these complexes, speciation diagrams were calculated for the complexes at temperatures ranging from 293 to 323 K.