Nickel hydroxide obtained by high-temperature two-step synthesis as an effective material for supercapacitor applications

Hybrid supercapacitors with nickel hydroxide electrode are widely used as modern power sources for electrovehicles, ignition of different electric engines, etc. Nickel hydroxide for supercapacitor use must satisfy special features which are quite different from those requested for battery application. The aim of this work is to improve the promising two-stage high-temperature method by altering hydrolysis condition (hot and cold) in order to obtain Ni(OH)₂ with improved electrochemical activity. Ni(OH)₂ samples have been investigated by PXRD, TG, DSC, SEM, TEM, cyclic voltammogramm, and galvanostatic charge-discharge cycling. It has been established from PXRD, TG, and DSC analyses that material obtained by hydrolysis at high temperature is a highly crystalline β-Ni(OH)₂ characterized by high thermal stability. Materials prepared by cold hydrolysis are a highly defective β_bc-Ni(OH)₂, with 6.3 % water content and a lower thermal stability. It has been shown that samples prepared by hot hydrolysis have a high redox reversibility and electrochemical cycling stability, but a lower electrochemical capacity. This suggests that the electrochemical processes are localized in the thin layer at the particle surface. Cyclic voltammograms of samples prepared by cold hydrolysis exhibit gradual activation of the active material, anyhow resulting in higher capacity. By means of the galvanostatic charge-discharge curves at different current densities, the specific capacities of the samples have been calculated. The sample prepared by cold hydrolysis has higher specific capacities than the sample prepared by hot hydrolysis.     

IndecomposableA-module summands inH * V which are unstable algebras

Letp be a prime and denote byA the modp Steenrod algebra. We determine the indecomposableA-module summands ofH*((ℤ/p)) ^d ;F _p which admit the structure of an unstableA-algebra. In fact, it turns out that this is equivalent to the problem of determining those indecomposableA-module summands which arise as the modp cohomology of a space (or even a classifying space of a finite group). We reduce this problem to one in modular representation theory, namely for whichd andp is the projective cover of the trivial one dimensional GL(d,F _p ) representationF _p a permutation module. Our solution of this latter problem makes use of the classification of subgroups of GL(d,F _p ) acting transitively on (F _p ) ^d \{0} and hence depends on the classification of finite simple groups (on Feit-Thompson's odd order theorem ifp=2).     

Synthese von arsino-ketenen auf dem inether-weg

The arsino ketenes 3a–c are formed by the reaction of the arsino ynethers 1a and b with chlorodiphenylarsine and bromotriphenylgermane and by the reaction of the silylated ynether 1c with chlorodiphenylarsine.     

Electrical conductivity in a conductor 5 atoms thick

A single crystal 5 atoms thick comes close to the approximation of a quasi-two-dimensional system. Still, it retains some characteristics of the bulk material as revealed by the virtual absence of any contact effects as long as the contacts consist of thicker areas of the same crystal. Electrical conductivity and electron mobility are strongly influenced by adsorption on the surface. The onset of an additional conduction process at high current density and low temperature is reported.     

Joined ellipsometry and voltametry investigation on the second discharge plateau in Ni(OH)2

The electrochemical properties of nickel hydroxide, produced via an electrodialysis process are studied by means of cyclic voltametry and in-situ ellipsometry methods. The Ni(OH)₂ electrodes are thin layers of nickel hydroxide powder deposited on a polished platinum substrate. Electrochemical and optical properties are investigated in a voltage domain including the so-called “second discharge process”. The reduction of nickel hydroxide proceeds at two successive potentials with a recovering of the initial optical data only after the second discharge step. The first discharge step leads to a nickel hydroxide not fully discharged while the second discharge step is coupled both to a sudden change in the nickel hydroxide properties and an agglomeration of particles phenomenon. Project financed by the E.U., program Brite Euram BRPR-CT97-0515 (NEARBY) Paper presented at the 7th Euroconference on Ionics, Calcatoggio, Corsica, France, Oct. 1–7, 2000.     

A Comparison of In‐Vitro and In‐Vivo Degradation of Poly(D,L‐lactide) Bio‐Absorbable Intra‐Medullary Plugs

Poly(D ,L ‐lactide) has been evaluated as a material for the manufacture of intra‐medullary plugs to be used in total hip arthoplasty. Plugs were manufactured by compression moulding and subjected to in‐vitro and in‐vivo degradation. In‐vitro hydrolysis was carried out by immersion in phosphate buffered saline (Ringer's solution) at 37°C and rates of degradation were relatively rapid with molecular weight halving after 30 days. In‐vivo degradation was assessed by implantation into dogs followed by retrieval at intervals up to 24 months. Molecular weight was found to reduce to half the original value in about 190 days. It is thought that this difference in degradation rate is because of diffusional control of the overall process. Histology showed that the implanted plugs were resorbed over 24 months.     

Permittivity and AC conductivity in yttria-stabilized zirconia

Alternating current (ac) conductivity and permittivity measurements were carried out on yttriastabilized cubic zirconia, with yttria varying from 9.6 to 25.5 mol%. In this composition range, the dielectric constant measured at 10³ Hz decreased from 29.8 to 23.2 as the yttria concentration increased. A plot of the ac conductivity versus frequency exhibited a plateau conductivity (_dc) and a frequency () dependent term '(). An analysis of '() with a suitable theoretical approach based on a pairs-approximation model, resulted in a calculated binding energy for the yttrium-associated oxygen vacancy of 0.29±0.05 eV, which compares favorably with values obtained by different means in previous studies. The experimental determination of the frequency dependence of the conductivity and its analysis provides an effective basis for understanding the ionic conductivity mechanism.