The effect of the cation nature is explored for the reaction of alkali metal ions intercalation into the AVPO4F material. Application of electrochemical methods allowed determining the key ...diffusional and kinetic parameters for Li+, Na+ and K+ intercalation reactions. The obtained formal redox potential values, apparent diffusion coefficients and charge transfer resistance values are contrasted, providing the possibility to assess the variation in the reaction energetics for metal ion insertion/extraction. The observed differences in reaction rates are rationalized in terms of different contributions of ion desolvation and transition through adsorbate layer/electrode interface for various ions.
The elucidation of the reaction rate-determining step nature in intercalation processes is essential for the development of approaches for the precise control of rate-limiting factors. In this work, ...we explore the kinetic patterns of lithium-ion intercalation into two model cathode materials (LiCoO2 and LiMn2O4) and develop criteria for distinguishing between Butler-Volmer slow charge transfer and slow chemical steps. A numerical model for the rate-limiting ion desolvation step is developed and the predictions of the model are compared with the experimental voltammetric and electrochemical impedance spectroscopy data. We show that slow desolvation step results in essential changes in the shape of both cyclic voltammetry and impedance responses with the kinetic resistance vs. potential dependencies being highly informative for the reaction rate control diagnostics. The consideration of the intercalation kinetics in four solvents (water, propylene carbonate, acetonitrile and dimethyl sulfoxide) allows concluding on the influence of the resistivity of surface layer/electrode material interface on the reaction slow step nature.
•Charge transfer rate vs. potential dependence is defined by the slow step nature.•Charge transfer rates depend sharply on the presence of SEI layers.•In SEI-free systems charge transfer rates are exceedingly fast.•Desolvation step results in a weak charge transfer rate vs. potential dependence.•Ion desolvation limiting step induces asymmetry in voltammetric responses.
We have developed a method of
J
/ψ reconstruction in the dielectron decay channel at protonnuclear (
p
-C and
p
-Au at an energy of 30 GeV) and nuclear-nuclear (Au-Au at an energy of 10 GeV/nucleon) ...collisions with the use of the CBM setup. The KFParticle package is used for reconstructing the topology of signal events. It is shown that the CBM setup allows accumulating considerable
J
/ψ statistics over a reasonable time interval at SIS100 energies.
The electrochemical insertion patterns of potassium‐rich Prussian blue (PB) materials with different compositions and particle sizes were systematically compared, which allows us to deduce ...correlations between the influence of particle morphology and material structure on the potassium‐ion insertion mechanisms in aqueous solutions. Although structural analysis indicates that no first‐order phase transitions occur for nanosized K‐rich Prussian blue particles upon potassium‐ion (de)insertion, the electrochemical data (galvanostatic charge/discharge, cyclic voltammetry, small‐ and large‐amplitude potential step experiments) suggest other outcomes related to the two‐phase insertion mechanism for all explored PB samples. However, even in a case whereby the phase transformation is not accompanied by abrupt changes in the crystal structure, the two‐phase mechanism dominates all of the essential practical characteristics of performance of this cathode material, such as hysteresis (overpotential) between charge and discharge steps and the measured diffusivities of potassium‐ions during charge and discharge. The formalism presented herein provides a basis for quantitatively assessing ion insertion and deinsertion parameters unique to PB analogues.
Looking beyond first impressions: Despite the fact that the structural analysis indicates no first‐order phase transitions occurring for nanosized K‐rich Prussian blue (PB) particles upon potassium‐ion (de)insertion, the electrochemical data suggest other outcomes related to the two‐phase insertion mechanism for the K‐rich PB samples with the major rate‐limitations being related to the sluggish nucleation kinetics.
A clustering problem for the coordinate detectors in the Compressed Baryonic Matter (CBM) experiment is discussed. Because of the high interaction rate and huge datasets to be dealt with, clustering ...algorithms are required to be fast and efficient and capable of processing events with high track multiplicity. At present there are two different approaches to the problem. In the first one each fired pad bears information about its charge, while in the second one a pad can or cannot be fired, thus rendering the separation of overlapping clusters a difficult task. To deal with the latter, two different clustering algorithms were developed, integrated into the CBMROOT software environment, and tested with various types of simulated events. Both of them are found to be highly efficient and accurate.
We apply chronoamperometry and cyclic voltammetry to trace the effect of the deposition potential on morphological and redox properties of N-substituted polypyrrole films on platinum and ITO in ...acetonitrile solutions. The goal of these experiments is to check whether certain principle trends observed in the course of the film growth can be used to monitor the deposition process and to control the features of the fabricated polymer. We use STM for morphology characterization, and estimate the film thickness from its redox response in background solution. For titanocene-substituted pyrrole, we compare current transients data on the anodic electropolymerization and the monomer reduction, in order to estimate the mass transport contribution to the polymerization current within various time domains (0.1 ms–1,000 s). On the basis of all these observations, we conclude on the existence of four characteristic regions of deposition current transients and assign them to certain steps in the oligomers formation and the film growth. The region of the current growth is discussed as well in terms of traditional nucleation models.
The present study is focused on the synthesis and investigation of Pt and Pt-Ru nanostructures templated by anodic aluminum oxide films. Samples of this sort may be considered in future as model ...electrode materials of high roughness and specific controllable nanostructural features. Nanostructure and morphology of electrodeposited materials are characterized using scanning electron microscopy and scanning tunneling microscopy techniques. A possibility to control catalytic activity of electrodeposits by means of templating is discussed as well. Higher catalytic activity of nanostructured Pt-Ru as compared to usual electrodeposit is very promising for further clarification of structural effects in electrocatalysis. In particular, newly proposed materials combine high roughness and the increased number of grain boundaries known to provide high catalytic activity of platinum group metals in certain processes. Future prospects of obtaining materials with even higher roughness factors are discussed.
Multicomponent electrodes composed of reticulated vitreous carbon (RVC), polyaniline (PANI) and palladium (Pd) were prepared by a two-step method and then investigated. In the sample synthesis cyclic ...voltammetry and chronoamperometry modes were subsequently applied. A strict procedure of sample synthesis and a model to estimate the partial loading values were established. The latter, allowed for precise coulometric determination of sample composition i.e. the amount of PANI (4–86
nmol/cm
2) and Pd (0.2–2.1
μmol/cm
2) in RVC/PANI/Pd electrode. Low PANI/Pd ratio (mainly ≪ 1) assured the predominating contribution of electrodeposition process as compared to possible chemical deposition. The presence of polymer affected the rate of Pd electrodeposition. The morphology and electrochemical properties of RVC/PANI/Pd and RVC/Pd systems were studied. SEM and STM images have shown that the amount of PANI in the sample influences the size and the distribution of palladium aggregates. The size of Pd crystals forming the aggregates was ca. 5
nm. Pd coalescent crystals tend to locate in the vicinity of polymer chains. Cyclic voltammograms of RVC/PANI/Pd were found to combine RVC/PANI and RVC/Pd electrochemical characteristic, with very slight mutual effect of components. RVC/PANI/Pd electrodes were studied with respect to hydrogen sorption abilities. RVC/PANI/Pd electrodes absorb smaller amounts of hydrogen in the β-phase than their RVC/Pd counterparts. The latter is caused by partial isolation of Pd in the course of absorption period, by reduced non-conducting PANI film.
Cathodic electrodeposition of oxides on platinum from MoO
3
–K
2
MoO
4
(3.85–75 mol% MoO
3
) under DC and pulsed galvanostatic modes is discussed in combination with voltammetry data. Characteristic ...potential values (as related to oxygen evolution onset) are reported for Mo(VI/IV) redox processes, as well as for electrochemical equilibria with participation of molybdenum metal and Pt–Mo alloys. On the basis of scan rate effects and results for various potential limits, and also of voltammetry with preliminary potentiostatic accumulation of products, molybdate reduction mechanism complicated by a chemical step of Mo metal oxidation is proposed. This qualitative assumption is verified in preparative electrolysis experiments with products identification by means of X-ray diffractometry, scanning electron microscopy, and EDX local analysis. Deposition under pulsed mode is found to be useful tool to adjust the duration of chemical step and by these means to alter the composition of final products. The conditions supporting the formation of MoO
2
and more reduced oxides are formulated.
