15 research outputs found
Genetic analyses of the electrocardiographic QT interval and its components identify additional loci and pathways
The QT interval is an electrocardiographic measure representing the sum of ventricular depolarization and repolarization, estimated by QRS duration and JT interval, respectively. QT interval abnormalities are associated with potentially fatal ventricular arrhythmia. Using genome-wide multi-ancestry analyses (>250,000 individuals) we identify 177, 156 and 121 independent loci for QT, JT and QRS, respectively, including a male-specific X-chromosome locus. Using gene-based rare-variant methods, we identify associations with Mendelian disease genes. Enrichments are observed in established pathways for QT and JT, and previously unreported genes indicated in insulin-receptor signalling and cardiac energy metabolism. In contrast for QRS, connective tissue components and processes for cell growth and extracellular matrix interactions are significantly enriched. We demonstrate polygenic risk score associations with atrial fibrillation, conduction disease and sudden cardiac death. Prioritization of druggable genes highlight potential therapeutic targets for arrhythmia. Together, these results substantially advance our understanding of the genetic architecture of ventricular depolarization and repolarization
Genetic analyses of the QT interval and its components in over 250K individuals identifies new loci and pathways affecting ventricular depolarization and repolarization
IN SITU X-RAY ABSORPTION SPECTROSCOPY STUDY OF TIN ANODE NANOMATERIALS FOR LITHIUM-ION BATTERIES
Tin is an attractive alternative to replace traditional carbon based anodes in lithium-ion batteries (LIBs) due to the nearly three-fold increase in theoretical capacity over carbon. However, metallic tin suâ”ers from volumetric expansion of the crystal structure during initial lithium insertion that quickly degrades the material and reduces the performance of the battery. Various techniques have been previously investigated with the goal of suppressing this destructive expansion by incorporating oxygen or a lithium-inactive metal into the tin to provide structural support and mitigate volumetric expansion. These materials show increased capacity retention compared to metallic tin, but still suâ”er from capacity fading. The nature of these structural degradations must be fully understood to permit engineering of materials that avoid these destructive tendencies and can be considered as viable options for LIBs. In situ X-ray absorption spectroscopy (XAS) measurements were acquired on Sn, SnO2, Sn3 O2(OH)2, Cu6Sn5 and Ni3Sn4 nanoparticle anodes for LIBs. Accompanying the electrochemical characterization conducted on each material, the local atomic structure was modeled as a function of potential during the first charge and also as a function of charged/discharged states for several cycles. The extended X-ray absorption fine structure (EXAFS) theoretical modeling included the first unambiguous observation of Sn-Li coordination numbers and atomic distances in tin-based anode materials. From correlating the electrochemical performance to the EXAFS analysis, the long-term capacity retention of tin-based anodes is dependent on the structural deformations that occur during the first charge. The conversion of oxygen to amorphous Li2O, and the network that it forms, has a dramatic eâ”ect on the kinetics of the system and the stability of the local metallic tin structure.Ph.D. in Physics, May 201
In Situ Xâray Absorption Spectroscopy Study of the Capacity Fading Mechanism in Hybrid Sn<sub>3</sub>O<sub>2</sub>(OH)<sub>2</sub>/Graphite Battery Anode Nanomaterials
In
situ X-ray absorption spectroscopy (XAS) of an electrode material
under electrochemical control has enabled a detailed examination of
the capacity fading mechanism during chargeâdischarge cycling
in a hybrid nanomaterial, Sn<sub>3</sub>O<sub>2</sub>(OH)<sub>2</sub>/graphite, that is considered for use as a high-capacity lithium-ion
battery anode. By the use of an original one-pot solvothermal synthesis
technique, Sn<sub>3</sub>O<sub>2</sub>(OH)<sub>2</sub> nanoparticles
were directly deposited on the surface of nanothin graphite and were
charged/discharged in situ for several cycles while XAS spectra at
the Sn K-edge were taken. Modeling of the collected extended X-ray
absorption fine structure (EXAFS) spectra provides detailed information
on the SnâO, SnâSn, and SnâLi coordination numbers
and atomic distances for each charged and discharged electrode state.
On the basis of electrochemical data and the changes in atomic arrangement
deduced from the EXAFS fitting results, including the first unambiguous
observation of SnâLi near neighbors, a capacity fading mechanism
is proposed that is different from widely accepted volume expansion
for tin metal and tin oxides. Our experimental results suggest that
atomic clusters of metallic tin surrounded by highly disordered Li<sub>2</sub>O shells are formed on first charge. The metallic tin clusters
participate in lithiation and delithiation on the following charge/discharge
cycles; however, because of continued segregation of tin and Li<sub>2</sub>O phases, the tin clusters eventually lose electrical contact
with the rest of the electrode and become excluded from further participation
in electrochemical reactions, resulting in reduced capacity of this
anode material
Potential-Resolved In Situ Xâray Absorption Spectroscopy Study of Sn and SnO<sub>2</sub> Nanomaterial Anodes for Lithium-Ion Batteries
This
work provides detailed analysis of processes occurring in
metallic Sn and SnO<sub>2</sub> anode materials for lithium ion batteries
during first lithiation, studied in situ with rapid continuous X-ray
absorption spectroscopy (XAS). The X-ray absorption near edge structure
(XANES) and extended X-ray absorption fine structure (EXAFS) spectra
provide information on dynamic changes in the Sn atomic environment,
including type and number of neighboring atoms and interatomic distances.
A unique methodology was used to model insertion of Li atoms into
the electrode material structure and to analyze the formation of SnLi
phases within the electrodes. Additionally, analysis of fully lithiated
and delithiated states of Sn and SnO<sub>2</sub> electrodes in the
first two cycles provides insight into the reasons for poor electrochemical
performance and rapid capacity decline. Results indicate that use
of SnO<sub>2</sub> is more promising than metallic Sn as an anode
material, but more effort in nanoscale and atomic engineering of anodes
is required for commercially feasible use of Sn-based materials
In Situ Ru KâEdge Xâray Absorption Spectroscopy Study of Methanol Oxidation Mechanisms on Model Submonolayer Ru on Pt Nanoparticle Electrocatalyst
In situ X-ray absorption spectroscopy
(XAS) with electrochemical
reaction control has enabled a detailed investigation of the mechanism
of the methanol electrooxidation by a bimetallic PtRu catalyst. By
the use of an original electrodeposition technique, ca. 0.3 monolayer
of Ru was deposited on the surface of unsupported Pt nanoparticles
(Ru@Pt). The presence of Ru atoms only at the surface of nanoparticles
turns a bulk sensitive XAS technique into a surface methodology which
permits correlation of the X-ray absorption fine structure at the
Ru K-edge to the role of Ru atoms in the methanol oxidation process.
In situ XAS spectra of the Ru@Pt nanoparticles were collected at various
electrode potentials in background electrolyte, and then in 1 M solution
of methanol (CH<sub>3</sub>OH) in the same electrolyte. Significant
differences in the catalyst state have been revealed between these
two environments. In the background electrolyte, Ru gradually oxidizes
from mostly metallic to a RuÂ(III)/RuÂ(IV) mixture at the highest potentials.
In the presence of CH<sub>3</sub>OH, the Ru oxidation state remains
a mixture of metallic and RuÂ(III) even at the highest potentials.
CO-type species were found adsorbed on Ru atoms at all potentials
and coadsorbed with OH species at potentials 0.175 V vs Ag/AgCl and
higher with steady number of near neighbors. The same potential correlates
to the beginning of methanol oxidation reaction observed electrochemically.
Therefore coadsorption of CO and OH groups on Ru atoms appears to
be critical in the methanol oxidation process. The need for OH groups
for CO removal from Pt sites was previously suggested by the bifunctional
CH<sub>3</sub>OH oxidation mechanism; however, occupancy of Ru atoms
with CO species and direct structural observations of the coadsorption
of CO and OH on the same Ru atom is a novel finding resulting from
this study. Other changes in the catalyst environment were observed,
including decreased RuâRu and RuâPt bond distances,
increased numbers of RuâPt near neighbors, and decreased number
of RuâRu near neighbors
Surface Modification Approach to TiO<sub>2</sub> Nanofluids with High Particle Concentration, Low Viscosity, and Electrochemical Activity
This
study presents a new approach to the formulation of functional
nanofluids with high solid loading and low viscosity while retaining
the surface activity of nanoparticles, in particular, their electrochemical
response. The proposed methodology can be applied to a variety of
functional nanomaterials and enables exploration of nanofluids as
a medium for industrial applications beyond heat transfer fluids,
taking advantage of both liquid behavior and functionality of dispersed
nanoparticles. The highest particle concentration achievable with
pristine 25 nm titania (TiO<sub>2</sub>) nanoparticles in aqueous
electrolytes (pH 11) is 20 wt %, which is limited by particle aggregation
and high viscosity. We have developed a scalable one-step surface
modification procedure for functionalizing those TiO<sub>2</sub> nanoparticles
with a monolayer coverage of propyl sulfonate groups, which provides
steric and charge-based separation of particles in suspension. Stable
nanofluids with TiO<sub>2</sub> loadings up to 50 wt % and low viscosity
are successfully prepared from surface-modified TiO<sub>2</sub> nanoparticles
in the same electrolytes. Viscosity and thermal conductivity of the
resulting nanofluids are evaluated and compared to nanofluids prepared
from pristine nanoparticles. Furthermore, it is demonstrated that
the surface-modified titania nanoparticles retain more than 78% of
their electrochemical response as compared to that of the pristine
material. Potential applications of the proposed nanofluids include,
but are not limited to, electrochemical energy storage and catalysis,
including photo- and electrocatalysis
Probing the Li Insertion Mechanism of ZnFe<sub>2</sub>O<sub>4</sub> in Li-Ion Batteries: A Combined XâRay Diffraction, Extended XâRay Absorption Fine Structure, and Density Functional Theory Study
We
report an extensive study on fundamental properties that determine
the functional electrochemistry of ZnFe<sub>2</sub>O<sub>4</sub> spinel
(theoretical capacity of 1000 mAh/g). For the first time, the reduction
mechanism is followed through a combination of in situ X-ray diffraction
data, synchrotron based powder diffraction, and ex-situ extended X-ray
absorption fine structure allowing complete visualization of reduction
products irrespective of their crystallinity. The first 0.5 electron
equivalents (ee) do not significantly change the starting crystal
structure. Subsequent lithiation results in migration of Zn<sup>2+</sup> ions from 8a tetrahedral sites into vacant 16c sites. Density functional
theory shows that Li<sup>+</sup> ions insert into 16c site initially
and then 8a site with further lithiation. Fe metal is formed over
the next eight ee of reduction with no evidence of concurrent Zn<sup>2+</sup> reduction to Zn metal. Despite the expected formation of
LiZn alloy from the electron count, we find no evidence for this phase
under the tested conditions. Additionally, upon oxidation to 3 V,
we observe an FeO phase with no evidence of Fe<sub>2</sub>O<sub>3</sub>. Electrochemistry data show higher electron equivalent transfer
than can be accounted for solely based on ZnFe<sub>2</sub>O<sub>4</sub> reduction indicating excess capacity ascribed to carbon reduction
or surface electrolyte interphase formation
Dispersion of Nanocrystalline Fe<sub>3</sub>O<sub>4</sub> within Composite Electrodes: Insights on Battery-Related Electrochemistry
Aggregation
of nanosized materials in composite lithium-ion-battery
electrodes can be a significant factor influencing electrochemical
behavior. In this study, aggregation was controlled in magnetite,
Fe<sub>3</sub>O<sub>4</sub>, composite electrodes via oleic acid capping
and subsequent dispersion in a carbon black matrix. A heat treatment
process was effective in the removal of the oleic acid capping agent
while preserving a high degree of Fe<sub>3</sub>O<sub>4</sub> dispersion.
Electrochemical testing showed that Fe<sub>3</sub>O<sub>4</sub> dispersion
is initially beneficial in delivering a higher functional capacity,
in agreement with continuum model simulations. However, increased
capacity fade upon extended cycling was observed for the dispersed
Fe<sub>3</sub>O<sub>4</sub> composites relative to the aggregated
Fe<sub>3</sub>O<sub>4</sub> composites. X-ray absorption spectroscopy
measurements of electrodes post cycling indicated that the dispersed
Fe<sub>3</sub>O<sub>4</sub> electrodes are more oxidized in the discharged
state, consistent with reduced reversibility compared with the aggregated
sample. Higher charge-transfer resistance for the dispersed sample
after cycling suggests increased surface-film formation on the dispersed,
high-surface-area nanocrystalline Fe<sub>3</sub>O<sub>4</sub> compared
to the aggregated materials. This study provides insight into the
specific effects of aggregation on electrochemistry through a multiscale
view of mechanisms for magnetite composite electrodes