60 research outputs found
Neutronenstreuung an Hydriden intermetallischer Verbindungen
This review surveys the application of neutron scattering for the investigation of the microscopic behaviour of hydrogen in intermetallic compounds. This concerns the structure as well as the dynamics. Neutron diffraction experiments were performed on Ti, Mn. 0D and LaNi D-,. In the latter case the dominant nickel scattering could be suppressed by Isotope Substitution with Ni, anc [the anisotropic broadening of the Bragg peaks could be modelled in a correspondingly modified Rietveld-profile refinement. For the investigation of hydrogen diffusion in intermetallic hydrides by means of quasielastic neutron scattering an iterative multiple scattering correction procedure has been developped which allows a reliable determination of hydrogen diffusion coefficients. The mechanism of hydrogen diffusion in intermetallic hydrides comprises three types of jumps: escape jumps out of energetically lower interstitials, transport jumps over the energetically higher sites and locally restricted jump processes. For Ti Mn, H the 1. Z 1. o j main features of the diffusional behaviour could be described quantitatively in the framework of a three State model. By means of neutron vibrational spectr'oscopy Information about the occupied hydrogen sites and thus about the structure can be extracted from the symmetry Splitting of the vibrational modes. In this way we showed that in a-LaNi H La Ni,-octahedral and La Ni.-tetrahedral interstitial sites are occupied. 2 4 2 2 r We have used the novel posslbilities provided to neutron scattering by the new spallation sources in an investigation on Ă-V2 H. Using a unique Single domain Single crystal, for the first time we determined the directions of the fundamental excitations of a hydrogen atom in a metal. Overtones of these vibrations were observed up to 14th order. They establish a well defined H potential up to more than 1 eV. The sequence of excitations could be described quantitatively in terms of an empirical potential. Using the same sample we have also performed the first neutron Compton scattering experiment on a metal hydride. With this novel neutron scattering technique the momentum distribution and therefore - at low temperature -the ground State wave function is measured. The thus determined kinetic hydrogen energy is in good agreement with that calculated from the spectro scopically determined ground State wave function
Introduction to Quasielastic Neutron Scattering
This tutorial introduction has been written for people who are not specialized in neutron scattering or in other scattering methods but who are interested and would like to get an impression and learn about the method of Quasielastic Neutron Scattering (QENS). The theoretical (scattering process) as well as the experimental basics (neutron sources, neutron scattering instruments, experimental periphery) are explained in a generally understandable way, with only the most essential formulas. QENS addresses the stochastic dynamics in condensed matter, and it is pointed out for which problems and for which systems in condensed matter research QENS is a powerful method. Thus sufficient information is provided to enable non-experts to think about their own QENS experiment and to understand related literature in this area of researc
Phosphonium-Based Polyelectrolytes: Preparation, Properties, and Usage in Lithium-Ion Batteries
Phosphorous is an essential element for the life of organisms, and phosphorus-based
compounds have many uses in industry, such as flame retardancy reagents, ingredients in fertilizers,
pyrotechnics, etc. Ionic liquids are salts with melting points lower than the boiling point of water.
The term âpolymerized ionic liquidsâ (PILs) refers to a class of polyelectrolytes that contain an ionic
liquid (IL) species in each monomer repeating unit and are connected by a polymeric backbone to
form macromolecular structures. PILs provide a new class of polymeric materials by combining some
of the distinctive qualities of ILs in the polymer chain. Ionic liquids have been identified as attractive
prospects for a variety of applications due to the high stability (thermal, chemical, and electrochemical)
and high mobility of their ions, but their practical applicability is constrained because they lack the
benefits of both liquids and solids, suffering from both leakage issues and excessive viscosity. PILs are
garnering for developing non-volatile and non-flammable solid electrolytes. In this paper, we provide
a brief review of phosphonium-based PILs, including their synthesis route, properties, advantages
and drawbacks, and the comparison between nitrogen-based and phosphonium-based PILs. As
phosphonium PILs can be used as polymer electrolytes in lithium-ion battery (LIB) applications, the
conductivity and the thermo-mechanical properties are the most important features for this polymer
electrolyte system. The chemical structure of phosphonium-based PILs that was reported in previous
literature has been reviewed and summarized in this article. Generally, the phosphonium PILs that
have more flexible backbones exhibit better conductivity values compared to the PILs that consist of a
rigid backbone. At the end of this section, future directions for research regarding PILs are discussed,
including the use of recyclable phosphorus from waste
Sustainable Electrochemical Depolymerization of Lignin in Reusable Ionic Liquids
Ligninâs aromatic building blocks provide a chemical resource that is, in theory, ideal for substitution of
aromatic petrochemicals. Moreover, degradation and valorization of lignin has the potential to generate
many high-value chemicals for technical applications. In this study, electrochemical degradation
of alkali and Organosolv lignin was performed using the ionic liquids 1-ethyl-3-methylimidazolium
trifluoromethanesulfonate and triethylammonium methanesulfonate. The extensive degradation of
the investigated lignins with simultaneous almost full recovery of the electrolyte materials provided
a sustainable alternative to more common lignin degradation processes. We demonstrate here that
both the presence (and the absence) of water during electrolysis and proton transport reactions had
significant impact on the degradation efficiency. Hydrogen peroxide radical formation promoted certain
electrochemical mechanisms in electrolyte systems âcontaminatedâ with water and increased yields of
low molecular weight products significantly. The proposed mechanisms were tentatively confirmed by
determining product distributions using a combination of liquid chromatography-mass spectrometry
and gas-chromatography-mass spectrometry, allowing measurement of both polar versus non-polar as
well as volatile versus non-volatile components in the mixtures
Synthesis and electrochemistry of remotely thioetherâfunctionalized disilenes
We report the synthesis of p-methylthio-functionalized disilenes with (oligo)phenylene-linkers of different sizes between the thiomethyl group and the Si=Si moiety. 29Si NMR and UV/vis data suggests that the linker-size affects the Si=Si moiety only moderately. Cyclic voltammetry reveals an increasing number of reduction events with the number of phenylene rings, which are therefore clearly associated to the oligo(phenylene) linking unit. The exchange current density of the oxidation and reduction reactions as determined by linear sweep voltammetry with a rotating disc electrode also shows significant differences between the prepared disilenes
Novel Phosphonium-Based Ionic Liquid Electrolytes for Battery Applications
In this study, we address the fundamental question of the physicochemical and electrochemical properties of phosphonium-based ionic liquids containing the counter-ions bis(trifluoromethanesul
fonyl)imide ([TFSI]â) and bis(fluorosulfonyl)imide ([FSI]â). To clarify these structureâproperty as
well as structureâactivity relationships, trimethyl-based alkyl- and ether-containing phosphonium
ILs were systematically synthesized, and their properties, namely density, flow characteristics, alkali
metal compatibility, oxidative stability, aluminum corrosivity as well as their use in Li-ion cells
were examined comprehensively. The variable moiety on the phosphonium cation exhibited a chain
length of four and five, respectively. The properties were discussed as a function of the side chain,
counter-ion and salt addition ([Li][TFSI] or [Li][FSI]). High stability coupled with good flow characteristics were found for the phosphonium IL [P1114][TFSI] and the mixture [P1114][TFSI] + [Li][TFSI],
respectively
Novel Phosphonium-Based Ionic Liquid Electrolytes for Battery Applications
In this study, we address the fundamental question of the physicochemical and electrochemical
properties of phosphonium-based ionic liquids containing the counter-ions bis(trifluoromethanesul
fonyl)imide ([TFSI]) and bis(fluorosulfonyl)imide ([FSI]). To clarify these structureâproperty as
well as structureâactivity relationships, trimethyl-based alkyl- and ether-containing phosphonium
ILs were systematically synthesized, and their properties, namely density, flow characteristics, alkali
metal compatibility, oxidative stability, aluminum corrosivity as well as their use in Li-ion cells
were examined comprehensively. The variable moiety on the phosphonium cation exhibited a chain
length of four and five, respectively. The properties were discussed as a function of the side chain,
counter-ion and salt addition ([Li][TFSI] or [Li][FSI]). High stability coupled with good flow characteristics
were found for the phosphonium IL [P1114][TFSI] and the mixture [P1114][TFSI] + [Li][TFSI],
respectively
Structure-Property Relation of Trimethyl Ammonium Ionic Liquids for Battery Applications
Ionic liquids are attractive and safe electrolytes for diverse electrochemical applications
such as advanced rechargeable batteries with high energy densities. Their properties that are
beneficial for energy storage and conversion include negligible vapor-pressure, intrinsic conductivity
as well as high stability. To explore the suitability of a series of ionic liquids with small ammonium
cations for potential battery applications, we investigated their thermal and transport properties.
We studied the influence of the symmetrical imide-type anions bis(trifluoromethanesulfonyl)imide
([TFSI]â) and bis(fluorosulfonyl)imide ([FSI]â), side chain length and functionalization, as well as
lithium salt content on the properties of the electrolytes. Many of the samples are liquid at ambient
temperature, but their solidification temperatures show disparate behavior. The transport properties
showed clear trends: the dynamics are accelerated for samples with the [FSI]â anion, shorter side
chains, ether functionalization and lower amounts of lithium salts. Detailed insight was obtained
from the diffusion coefficients of the different ions in the electrolytes, which revealed the formation
of aggregates of lithium cations coordinated by anions. The ionic liquid electrolytes exhibit sufficient
stability in NMC/Li half-cells at elevated temperatures with small current rates without the need
of additional liquid electrolytes, although Li-plating was observed. Electrolytes containing [TFSI]â
anions showed superior stability compared to those with [FSI]â anions in battery tests
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